AF 447 Thread No. 7

[DozyWannabe]

Lyman, if you're going to continue to make such wild extrapolations, I honestly don't see the point.

We know the ADI on the LHS was OK from the DFDR, and the ISIS seems to have been OK too, otherwise the Captain would not have pointed it out. When the Captain comes in, the PF's stick is all the way back and remains so for another 30 seconds, during which time the PF is actually talking to the PNF and the Captain (and at one point tries to extend the speedbrakes). This is a mushing stall and the ADI is varying considerably in pitch and bank as the aircraft tries to get it's nose down (which the PF is almost constantly counteracting). It would appear that they focus on the lateral problems to the exclusion of all else, and the question of pitch doesn't even seem to come into it until they are passing through 10,000ft.

Despite no indications (and a pretty strong counterindication from the stall warning), the PF seems convinced they are in an overspeed situation initially, and following that incorrect intuition consistently applies a recovery technique which is the precise opposite of what he should be doing, unwittingly putting them further and further outside of the flight envelope. By the time the Captain arrives, nothing seems to make sense, but the PF continues to pull.

I'm pretty sure it's not a case of the PF's instruments telling lies, I think that both EFIS and the ISIS were telling the truth, but the truth made no sense to them because nobody asked the right questions. Arguments over yokes aside, the question of "what are you doing?" was never asked, and by the time the PF volunteered the information it was too late.

@jcjeant - Earlier in the sequence, the PNF seems to have a better handle on things (and it's a reasonable assumption that his anxiety for the Captain to return is related to that - he's not happy with the performance of the guy the Captain implicitly put in charge). By the time the exchange where the PF says he's been pulling up for some time happens, confusion seems to have overtaken all three crewmembers.

[Old Carthusian]

Lyman
I think the key here is the people not the instruments. None of them show any real understanding of the situation they're in. As I mentioned perception is a vital factor and it looks like none of them could be described as being in a state where they could perceive correctly. Others have written of the natural impulse to pull back on the stick and this seems to be the PF's reaction. Initially as I have pointed out the PNF was telling the PF to go down without effect. By the time the Captain arrived the PNF had also succumbed to panic and was not coherent.

[jcjeant]

Hi,

I think the key here is the people not the instruments

At the end .. the human factor investigation team will certainly conclude (IMO) as a case of hypervigilance and tunnel vision (results of stress , fear and panic)

[Drmedic]

@Dozy
Your summon up in #251 is imo totally correct. Hopefully BEA will come to the same conclusion in their final report.

[CONF iture]

Not if the AoA gets the value zero for <60 kCAS.
Not too sure to get that HN39 ... at zero of AoA aircraft is not stalled.

airtren, would you be kind enough to let me know how you proceed to be able to present the data in a different order (http://www.pprune.org/6619021-post2571.html).

[CONF iture]

By grabbing the controls with little or no warning you risk startling your colleague, which is in fact incredibly dangerous and you could end up "fighting" each other.
"I HAVE CONTROL" - no more - no less - no anbiguity
Forget your 'incredibly dangerous'

One of the advantages to the sidestick system is that by holding the priority button you can "lock out" the other stick if you need to.
Only partially true - If a fight there is, both fighters could endlessly retake control.

@CONF - Or you could have had a split elevator condition (as in EgyptAir990) and a nasty crash.
If there was a 'split elevator + nasty crash' every time a change of control is done on short final we should know it by now ...

[Machinbird]

Excuse me for interrupting this excellent dog fight.:rolleyes:
It occurs to me, that 3 months from the news conference that introduced the 3rd BEA report on AF447 has more than elapsed. At that briefing Jean-Paul Troadec introduced their new recommendations with the following (translated) comment:

First of all, a word or two about what it means to issue a recommendation. A recommendation is not a pious wish from the BEA. A recommendation is something that we make, of course, when we think that it is useful for safety but also that has a reasonable chance of being implemented. Because when we make a recommendation to an authority in general, it must answer us within three months and provide us with the follow up that it intends to give to this recommendation. So, this is something that commits us that also now commits the authority since the implementation of the new European regulation on accident investigations.

The underlined portion has my interest. What is the upshot of the recommendations? Has anyone seen anything?

[airtren]

AirTren
No that isn't my thought at all. Perception works differently for different people and some actually process audio signals quicker than visual signals.
We've established earlier that the sounds of a couple or several words needed to describe the new position of a cockpit control takes several seconds.

Therefore, the perception of those sounds, those words, cannot take less time than it took to produce them, and that is several seconds.

I don't think a person that needs more than the above several seconds to perceive a new position of a cockpit control will be considered as not having vision problems and allowed to fly commercial passenger airplanes..

Furthermore you don't transform an audio signal into a visual signal unless that is what you want to do. This is a fallacy - sound is sound and is interpreted as such. The transform is done involuntarily, and unconsciously. You may not be aware it happens.

The change of the position of a cockpit control is a spacial element, which can be perceived directly without translation, only visually, or tactile. An articulated sound perception - a series of words - is not a spacial perception. Therefore a translation/transform takes place.

[HazelNuts39]

... at zero of AoA aircraft is not stalled.Exactly! Some time ago someone (A33Zab, IIRC) explained that the stall warning stops because the ADR outputs AoA=0 when airspeed is <60 kCAS.

[Old Carthusian]

AirTren
This is not what I say at all - what the statement says is that some people PROCESS audio signals quicker than they process visual signals. You could say that their hearing functions at a higher rate then their vision if you wanted to simplify. The processing and interpretation of the signal are the significant factors not the receipt or transmission of the signal. Some people will even respond to an audio signal whilst they may overlook a visual cue. In fact visual cues are often missed - a simple example, think of the times you've missed someone waving at you but responded when they spoke to you.

[airtren]

AirTren
This is not what I say at all - what the statement says is that some people PROCESS audio signals quicker than they process visual signals. You could say that their hearing functions at a higher rate then their vision if you wanted to simplify. The processing and interpretation of the signal are the significant factors not the receipt or transmission of the signal. Some people will even respond to an audio signal whilst they may overlook a visual cue. In fact visual cues are often missed - a simple example, think of the times you've missed someone waving at you but responded when they spoke to you.

Please read carefully - re-read - what I wrote, as I explained my interpretation of what you wrote.

I don't think we refer to the same people, which is commercial airline pilots, which need to meet certain medical requirements.

I had the luck from an early age to be in contact with airplane flying professionals, and know since I can remember their visual and word perception abilities.

I never experienced the example of your post.

[Old Carthusian]

AirTren
I would say it might be thought a trifle dishonest to edit your comments and then claim that they were your original thoughts.
Be that as it may - I am not referring to visual impairment or otherwise. I am referring to how perception and interpretation work which varies from person to person. It is not a fixed process and it is perfectly possible for people to respond in different ways to different sources of stimulus. Comprehension does not always come immediately and this is the point that needs to be remembered.
A sound is a sound signal - if you wish to transform it into a visual signal you can do but it is conscious. If you don't it stays a sound signal. One does not listen to music and transform the signals into visual stimulae unless one wants to.

[airtren]

A number of additions, to fill in the holes:


A system in software is called a “software system” . Once the marketing and requirements phases are completed, a software system gets defined as a product by a product definition and architecture group. A Software System Architecture Specification and a Functional Specification are developed, which provide a full map of all the functional blocks of the software system, the major algorithms, and their interactions, inputs data flow, and output data flow, as well as how map of its functions, respectively how they are controlled, managed, monitored, etc... A major element part of these specifications can be the type of real, or virtual hardware platforms on which the software will run. Designing the software for each functional block may be assigned to smaller groups. Functional Block Software Architecture Specifications may be developed, along with Block Functional Specifications. Algorithms are further specified in minutia details, It is followed by a Software Development Specifications, which defines the software mechanisms to be employed for implementing the algorithms and desired functionality in software. In parallel, there is a Quality and Test Plan Specification as one, or as two different documents, each defining the steps and tools to achieve the quality and testing targets. The software development – writing the programs - is done based on the latter, with unit testing done in multiple stages, from unit to system testing. Important to note that the Functional Specifications are the basis of the User Documentation development, which end up carrying most of the information of those specs..







For an airplane, the process is many times more complex, as the process multiplies, and there are so many specific technologies involved besides software. The requirements are external and internal – yes, company internal groups, from research, to manufacturing participate at defining a new product. An airplane system definition and architecture specifications is very complex, containing a a map of the various functional blocks of the airplane, etc… It is further divided into subsystem definition and architecture specifications.





For the airplane command and control subsystem, there is an subsystem architecture specification that goes into the details of the subsystem, defining the algorithms,





For larger airplane manufactures is not unusual to have the product specification done in paralele with the product simulation. Super-computers, and special programming languages, and compilers are used for modeling, and simulation of the functional blocks of the airplane, so that software can be run and the functioning of the functional blocks can be tested, and verified, through modeling, and simulation, long before any hardware piece has been physically ready for such a thing. It’s amazing, mind boggling….






The modeling and simulation during product development can be done even just for software systems, if the software systems are very large, and if the hardware platforms are developed in parallel, or not available immediately.







This is believe it or not... a very brief summary....

[airtren]

AirTren
I would say it might be thought a trifle dishonest to edit your comments and then claim that they were your original thoughts.

The text posted originally before it should have, so as it was not what I intended, I performed an editing right away, which took a couple of minutes. I saw your post only after finishing the edit, and it seems you probably caught my original post, while I was editing it.

While I am sorry for this to be confusing to you, I think you're exaggerated in your accusation which is gratuitous, particularly when I've spend extensive time to understand what you're saying, and trying to respond, so that could have a decent dialog.

Be that as it may - I am not referring to visual impairment or otherwise. I am referring to how perception and interpretation work which varies from person to person. It is not a fixed process and it is perfectly possible for people to respond in different ways to different sources of stimulus. Comprehension does not always come immediately and this is the point that needs to be remembered.
A sound is a sound signal - if you wish to transform it into a visual signal you can do but it is conscious. If you don't it stays a sound signal. One does not listen to music and transform the signals into visual stimulae unless one wants to.People that are accepted as pilots are within well defined health requirements range. That does not mean that those that don't meet the requirements are impaired.

I am afraid our communication is not working well, as it seems to me that somehow you're not reading or getting the meaning of what I am writing, as your replies seem to be such a radical deviation from what I wrote. ..

The visual perception of a change of a "control" position which is so simple, and done within the normal training, and cockpit routine, does not require any sophisticated comprehension, nor does it expose any peculiarity with one's visual perception. Such "visual perception" is plentily demonstrated by its use on a large number of airplanes world wide.
.

[Lyman]

Progress, then. You take note of ISIS' accuracy by stating "because the Captain makes reference to it". Slight praise, and poor foundation. It was the duffward descent of the panel that caused the crash, do you not agree? Just as PF lost his PITCH sense when he first articulated the stick, the flight went South from that point. Are you conversant with the length of time the a/c was responding to its own problems with the incorrect speeds prior a/p loss?

For the record, I'd like to suggest a different perspective on the AirBus operation re: Pilotage. A pilot trains to fly, as a platform is built to be programmed. Once qualified to pilot a commercial a/c, he is typed.

Just like typing is necessary to program a platform, so is typing necessary to meld Human/Bus. Perhaps other a/c as well. My suggestion is this. The Airbus is NOT just a conventional aircraft, and for different reasons, it was not intended to be similar.

The deadly enemy of airborne pilotage is Surprise. People spend years and small fortunes to learn the craft, most of which is directed at "staying ahead" of the airframe. Each of the UAS incidents, and this accident, are extreme condemnation of the Airbus busted approach at mitigating a known fault. Without belaboring this conclusion, suffice to say there is ample proof.

Not a single one of the UAS problems recorded inspires confidence in the platform. A generic foundation for criticism is the aircraft's tout. All aircraft will bite. This one has had a generation of marketing, and 'training', attempting to diminish the harsher side of the platform's performance.

[Old Carthusian]

AirTren
Certainly I accept your explanation and am sorry if I imputed too much to the changes.
My point is not about the type of people, qualifications or standards they have to meet. My point is about how people comprehend signals via various stimulae. It varies and we cannot be too dogmatic or assume that everyone will respond in the same way to the same stimulus. We cannot even assume that someone will respond the same way to an identical stimulus all the time. This affects all sectors of society and all professions. Aviation history is replete with accidents caused by pilots missing visual and/or aural cues. Even an otherwise excellent pilot may miss a cue on that one vital occasion and precipitate an accident. This however is drifting off the subject somewhat.
Perception, interpretation and comprehension play a far more important part than the nature of the visual or aural stimulus. If you set up a frame of reference you enhance the chances of a correct understanding of the situation. Sometimes direct is not the best.

[NARVAL]

Maybe this message is not exactly « technical » enough for the Tech log, but I think that training and experience, after all, are the key to explaining the difficulties met by the crew. So I hope you will show patience…
When I first started thinking, feeling wise, with all the time I needed and all the documents I could find, I thought…they were surprised, they were disoriented, the crew did not work as a crew, maybe they could have done better. But time passed, I learned surprising things on the plane, on its systems, on its protections, although I flew for years on the A320 family (from 318 to 321) and I was not especially lazy or complacent.
And in very recent times, I have talked to friends, captains who fly on the 330 or 340, and who are very serious and trustworthy. They told me that they learnt from that accident a lot of things they certainly did not know at the time. Things their training had not prepared them for. Facts that are well known to test pilots or military fighter pilots, but which you have no way to learn in a career where you start at nearly zero experience on the A320 and end on the A380.
For example, when in an unusual position, a stall, a spin, you move the controls to a position that you think useful…or that the airplane manufacturer recommends,and you wait. You wait for long seconds, until the new position of the flight controls gives a result. Then, eventually, you wait some more…Many airline pilots have never practised that, and have no knowledge of it. My friends certainly did not.And I will not hold it against them, I had the good luck to be a military pilot first, flying some strange airborne objects of all kinds, but that does not make me better (in fact I was a very average IFR pilot)…only that different experience was useful at times.
The stall warning ? None of my friends knew that it stops at low speed, by a mysterious agreement with the DGAC, when the certification rules say that it should only stop when the angle of attack becomes normal again.
The trim protection in low speed mode, in alternate law…forget it, nobody knew anything about it (the fact that it is speed and not angle of attack that inhibits the trim from running too far aft…alas there were no speeds available).
The decision to apply TOGA thrust (made on the second stall alarm) was perfecly applying the first step of the Stall procedure at the time. It happens that now, that is forbidden at altitude and the procedure has completely changed.
Knowledge of the aerodynamics of the stall on the A330…none at the time, and, even now, very cloudy (experts are now considering a pitch-up into the deep stall never encountered in flight testing).
The A330 was modified after the crash (those at air France anyway) to have a « dual Input « alarm when both pilots act on the sticks at the same time. It did not have that alarm on the night of the accident.
I think that we should keep in mind the very scant knowledge and training of the pilots at the time in the aerodynamics, stall recovery techniques, stall recognition…It was NEVER thought at the time that those planes could fly beyond the « approach to stall ». It was never thought either that the plane could « fly » with 40 degrees AOA and only 8 or 10 degrees of nose up.
So, of course the crew might have done better, but they certainly were not seriously prepared for what happened. May they rest in peace.

[TTex600]

Excellent post NARVAL! EXCELLENT

[RetiredF4]

Maybe this message is not exactly « technical » enough for the Tech log, but I think that training and experience, after all, are the key to explaining the difficulties met by the crew. So I hope you will show patience…

Wise words from a wise pilot.....

thank you sir!

franzl

[llagonne66]

Narval,

I beg to differ on your comment regarding the lack of dual input alarm on AF 447 that night.
If you go back to the CVR transcript in the #3 report, you'll find that the synthetic voice stated "DUAL INPUT" on five occurences : 2:13:23, 2:13:41, 2:13:43, 2:13:45 and 2:13:47.

[BOAC]

Narval - may I join the commendation of that post - perfectly placed in Tech Log in my judgement.

It is reassuring to see you say that, as I had hoped, pilots of these systems have learn much from this accident. I do hope that these lessons (plus those to be learnt by the manufacturer, trainers and operators) will mean that something useful, even if hideously costly, has come out of this accident.

[Dani]

Knowledge of the aerodynamics of the stall on the A330…none at the time, and, even now, very cloudy (experts are now considering a pitch-up into the deep stall never encountered in flight testing).

Narval, I agree with all you are saying (except that they didn't have dual input indications), but transport aircraft are never exposed to any of these flying condition, certainly not deadly ones like deep stall and aerobatics. If the certification authority required this, they would also have to consider other highly unusual maneuvers, like rolls (yes, certain designer tested it out...), inverted flight, spirals aso. This is no aerobatics aeroplane or fighter, and it has a rather limited flight envelope.

If the next crash ends up in inverted flight, are we asking certification for this condition?

As you say, emphasize has to be put on training, that crews are never going close to these flight conditions. If they are, give them the tools to get out of it.

btw everyone who ever did basic aerobatic training knows the "let the stick in its position" procedure (which is only valid for stall and spins, not for all attitudes). Me thinks we should teach some cadets more aerobatics...

Dani

[Lyman]

Acro, no. STALL recovery, no.

A full and complete brief on UAS, stabilization at a/p loss, and some esprit de corps, de minimus.

RADAR, lack of comms prox, a sane approach to fault recognition and mitigation, prioritization, Command process, a rethink of controls placement, benchmark and minimum instrumentation, and recurrent training on impaired panel, dual input block/annunc., BUSS refit immediately, AHI alt., sterile cockpit in ITCZ transit, ad infinitum.

Narval. You are a wise and important oasis of thought, many thanks.

[airtren]

airtren, would you be kind enough to let me know how you proceed to be able to present the data in a different order (http://www.pprune.org/6619021-post2571.html).

Please see your PM inbox.

[CONF iture]

Exactly! Some time ago someone (A33Zab, IIRC) explained that the stall warning stops because the ADR outputs AoA=0 when airspeed is <60 kCAS.
Ok thanks HN39, I think that is the post (http://www.pprune.org/6661937-post425.html) ?
Still, I don't get it as the AoA never reduced to 0 deg when speed was below 60kt and the warning stopped.

The way you write it (voluntary or not ?) as a binary system could make more sense to me :

ADR outputs AoA=0 if CAS below 60 : meaning no AoA data therefore no possible stall warning
ADR outputs AoA=1 if CAS above 60 : meaning AoA data therefore possibility for stall warning


It is also the way I understand it in the report :
When the measured speeds are below 60 kt, the measured angle of attack values are considered invalid and are not taken into account by the systems.

For the zero deg ... ?

[DozyWannabe]

For the zero deg ... ?

I think he means the AoA output of the ADR is zero literally, meaning no output rather than zero degrees - the data is discarded.

[EDIT : Thanks to HN39, he's found the post that clarified it. The AoA output is zeroed and the Sign/Status Matrix set to Non-Computable Data. Interested parties can get an overview here:

ARINC 429 - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/ARINC_429)

(Even I had trouble with some of the acronyms... :O)

]

[AlphaZuluRomeo]

Dozy (re: #201 (http://www.pprune.org/tech-log/468394-af-447-thread-no-7-a-11.html#post6806039))
I'm aware that some terms used are not the proper ones, but being on an aviation forum I felt OK to use them as intended by other posters. Besides, english is not my mothertongue.
So, about logical/algorythm errors: let's look at them from the end-user point of view, i.e. the flight crews in the present situation. To be honnest, I don't think the "clients" (pilots) do care if the problem is :
- a hole in the specifications
- a implementation bug
- another type of bug
- an hardware failure
They see the outcome, which is that from a pilot's point of view, the system is illogical.

Back to "my" four points:
Point 1] (non-inhibition of the nose-up autotrim when stall warning is active)
You said: "I can foresee a couple of situations off the top of my head where that could be more dangerous than letting the trim run."
Well, I cannot. Could you elaborate, please? I did the reasonning with: "Would a pilot (provided he's aware & not mental) trim up when the aircraft is (near) stalled?" I could not see a single reason/circonstances where the answer is "yes".
About complexity: Yes, such a feature would add one more logical test. It's not a big deal in my opinion. And, more important, it doesn't seem a big deal to Airbus either because the NU autotrim is inhibited in Normal Law when the pseudo equivalent of the S/W (namely: the AoA protection) is active (ref: FCOM A330). If they can implement it in Normal Law, the complexity argument is IMO moot in Alternate Law.

Point 2] (inhibition of the stall warning under 60kt IAS)
I would like to know if such an inhibition is present on other aircrafts, too. I'm afraid a lot more aircrafts than "just" the A330 do more or less the same, indeed.
Latching the S/W state with no AoA valid measure: Why not, but I'm not sure about the risks of a false positive, here.
Other way is perhaps to inform the crew (how: to be thought) that currently "AoA measure is invalid. Consequence: S/W inop". That far more simple to implement, and avoids the need to "assume" what the S/W state should be.

Point 3] (V/S switching source from air data to inertial (and back))
Yes, I'm sure the V/S source switched. There is such a parameter in the FDR traces : "VERTICAL SPEED SELECTED FROM ADR (1=ADR 0=IR)"
The V/S recorded (and I assume, displayed during the flight) is "erratic" when ADR is the source, but "stable" when IR is the source.
When the PF said "J’ai un problème c’est que j’ai plus de vario là" (02:11:58) that's ~10-15 seconds after the switch to ADR source, and the beginning of the erratic values...
Note that at the same time as the V/S first swith to ADR source & display erratic values, other parameters go erratic too: CAS, AoA, FPA... and the S/W stops. So I agree that the V/S go erratic at the same time the stall is well established.

Point 4] (non-inhibition of the F/Ds when an UAS situation is detected)
I've perhaps written to quickly about that one. If the F/Ds indeed are inhibited, that's good. The logic hole I saw there is that while A/P and A/THR are dropped (i.e. the crew must re-engage them manually if they want them back), the F/Ds seem to just go flagged, but come back "from themseleves" when the conditions seem back to good: Would it not be better to let the crew manually re-engage the F/Ds, having assessed the which data are good and which are not?

----------------

jcjeant (re: #202 (http://www.pprune.org/tech-log/468394-af-447-thread-no-7-a-11.html#post6806050))
One cannot hope a 100% reliable sensor. One can (must) work to go as near as possible to the 100%, but must know he cannot obtain it.
My position is one cannot advocate for dropping automation until a perfect sensor is available, unless the goal is to drop automation itself without saying it.
On the other hand, yes there seem to be problems with the certification criteria regarding the probes. If proved, then the industry should work on that. But by no mean calling to a "stop" until perfection is reached will be of some help IMO ;)

----------------

The A330 was modified after the crash (those at air France anyway) to have a « dual Input « alarm when both pilots act on the sticks at the same time. It did not have that alarm on the night of the accident.
I don't know what/who is your source on that, but based on the CVR transcript from AF447, it's wrong.

I'm not aware that TOGA is now forbidden at altitude? :ooh:
I'm aware, on the other hand, that the stall (old) procedure which was good only to an approach to stall condition is now reworked so that it's good in a stalled condition too, implying the "lower AoA" rule, most important/first action. :ok:

[CONF iture]

NARVAL,
I like your post too.
For the DUAL INPUT, obviously F-GZCP was equipped.
Maybe other A330/340s in the AF fleet were not.
Where I work, some airplanes are not modified, I was ignoring this, don't know if they will be either.

[Machinbird]

If the next crash ends up in inverted flight, are we asking certification for this condition?
Let us hope you are not being prescient. This could easily result from a number of scenarios. I would be a shame if protections got in the way of an attempt to roll to the nearest horizon. This relates to any FBW aircraft.

Narval gets a big :ok:. He has stated very compactly the state of general airline pilot knowledge in the period leading up to AF447.

D.P. Davies was spot on in describing how treacherous it is to experience a stall in a near level flight attitude.


http://home.comcast.net/%7Eshademaker/stallattitudeweb.jpg

[DozyWannabe]

I'm aware that some terms used are not the proper ones, but being on an aviation forum I felt OK to use them as intended by other posters. Besides, english is not my mothertongue.

Not a problem - it wasn't intended as a criticism of you or your writing, it was just a case of getting the terminology straightened out.

So, about logical/algorythm errors:
...
They see the outcome, which is that from a pilot's point of view, the system is illogical.

Absolutely - I'm all about the information-sharing though, for two reasons. Firstly, to a software guy, seeing minor inaccuracies like that would be a bit like you guys reading "The plane crashed because the pilot pulled on the wing flaps that make it climb or descend" in the papers - the difference is that in your case it's well-meaning, but it still gives me a nervous tic when I see it, so sorry about that. Secondly, we know journos trawl these pages, and the last thing we need is a headline like "PILOTS SAY COMPUTER ERROR AT HEART OF FATAL AIRBUS PLUNGE", or similar silliness.


Well, I cannot. Could you elaborate, please? I did the reasonning with: "Would a pilot (provided he's aware & not mental) trim up when the aircraft is (near) stalled?" I could not see a single reason/circonstances where the answer is "yes".

The problem (as you state below regarding another point, and as I think I said in my original reply) is with false positives. If a sensor jam or genuine technical error causes the stall warning to sound when the aircraft is neither at or near the stall, that solution would prevent the pilot from trimming up when he wanted or needed to. You're then faced with the option of holding attitude with the primary controls and thrust (which would be fatiguing) - or if the limit applied to autotrim only, forcing pilots who are not used to trimming manually to do so at altitude with an abnormal situation on their hands.

I don't know why the A320 sim limits the nose-up trim and the A330 didn't in this case. Someone suggested that the limit might be airspeed-dependent, but the TRE had failed both ADCs. It's a question to ask Airbus, for sure.

About complexity: Yes, such a feature would add one more logical test.

See airtren's post - it's a lot more involved than that, going right back to the specification and trying to define potential knock-on effects of the change.

it doesn't seem a big deal to Airbus either because the NU autotrim is inhibited in Normal Law when the pseudo equivalent of the S/W (namely: the AoA protection) is active (ref: FCOM A330). If they can implement it in Normal Law, the complexity argument is IMO moot in Alternate Law.

The protections are a separate subsystem entirely from the annunciation/warning subsystem. There is no overarching logic connecting them, which makes implementing such a change considerably harder. I can see where you're coming from, I just think that a hard limit on autotrim under certain flight control circumstances would make more sense.

Other way is perhaps to inform the crew (how: to be thought) that currently "AoA measure is invalid. Consequence: S/W inop". That far more simple to implement, and avoids the need to "assume" what the S/W state should be.

With an eager and switched-on crew, sure that'd work. But this crew in the wee hours appeared not to notice a Stall Warning that was blaring in their ears for nearly a minute. By the time the AoA values became invalid, the situation was pretty grim - what chance they'd notice the warning you suggest?

Yes, I'm sure the V/S source switched. There is such a parameter in the FDR traces : "VERTICAL SPEED SELECTED FROM ADR (1=ADR 0=IR)"

Thanks, it's been a while since I read it in depth (thought I've gone back to specific traces briefly since.


The logic hole I saw there is that while A/P and A/THR are dropped (i.e. the crew must re-engage them manually if they want them back), the F/Ds seem to just go flagged, but come back "from themseleves" when the conditions seem back to good: Would it not be better to let the crew manually re-engage the F/Ds, having assessed the which data are good and which are not?

I think that design decision is a compromise - i.e. after an abnormal situation like that, would the crew notice that FDs were available and switch them back on again? I think the idea there was that they'd bring the FD back once the data was good, it would then be up to the crew to either use, disregard or disable them.

Food for thought - thanks!

[HazelNuts39]

I think that is the post ?No, this is the post I had in mind:
AF 447 No.5 post#1729 (http://www.pprune.org/tech-log/456874-af-447-thread-no-5-a-87.html#post6625553)- The stall warning is processed in FWCs not FCPCs
- It's the ADR itself which sets AOA to 0° (SSM=NCD) if CAS is below 60 Kts.

(A. did already changed that with 'BUSS' option, AOA is always available [only SSM will be NCD if CAS <60Kts])
I'm not sure I understand the bit in brackets: does the mod apply to A/C with the BUSS option or to all A/C?

[OK465]

...that with 'BUSS' option, AOA is always available...

Always? I believe someone posted info that the ADR's have to be physically disabled thru the switches on the overhead before the BUSS is enabled.

BUSS 'appears' to be an 'on demand' EFIS displayed AOA indexer, the first 'S' in BUSS being a misnomer.

In any case this is not full time AOA.

I think the idea there was that they'd bring the FD back once the data was good, it would then be up to the crew to either use, disregard or disable them.

(my bold)

The 'disregard', as a matter of intent to operate that way, is just not done by any carriers west of Atlantis these days. 'Good' data can translate to inappropriate lateral, & particularly inappropriate default vertical steering commands. In the wild west, they're either 'on' providing pilot selected steering guidance in the 'appropriate' mode as confirmed by the FMA or 'OFF'.

PRM breakout procedures are a another prime example of the validity this requirement in order to preclude unintended vertical guidance commands. (This is not to say that an inappropriate steering command should not be recognized for whatever reason it should occur.)

He has stated very compactly the state of general airline pilot knowledge in the period leading up to AF447.

That may be a little 'broadbrushish'.

EDIT: I guess semantically with BUSS, AOA is always 'available' just not always viewable. :)

[Machinbird]

The problem (as you state below regarding another point, and as I think I said in my original reply) is with false positives. If a sensor jam or genuine technical error causes the stall warning to sound when the aircraft is neither at or near the stall, that solution would prevent the pilot from trimming up when he wanted or needed to. You're then faced with the option of holding attitude with the primary controls and thrust (which would be fatiguing) - or if the limit applied to autotrim only, forcing pilots who are not used to trimming manually to do so at altitude with an abnormal situation on their hands.
So Dozy, how do you explain the AOA inhibit of nose up trim in Normal Law? Why did the engineers decide that was sensible? Wasn't it because you could actually trim an aft cg aircraft into a stall?
What happens when the trim stops is you have to hold a pressure. If you don't want to hold the pressure, you can still reach down with your free hand and turn the trim wheel. No big deal, but it will have to be a conscious decision.

The protections are a separate subsystem entirely from the annunciation/warning subsystem. There is no overarching logic connecting them, which makes implementing such a change considerably harder. I can see where you're coming from, I just think that a hard limit on autotrim under certain flight control circumstances would make more sense. There are all manner of things that happen in a FBW aircraft that are not annunciated. If nose up trim stops because it senses a limiting AOA, that is a form of annunciation in itself, and from a piloting standpoint, that is very intuitive..

[Clandestino]

On a related subject, I have been in a 319 that failed to respond to SS input asking for nose down. I was maneuvering, avoiding one buildup and flew into another which was a substantial updraft. I had already pitched for green dot trying to climb above the first buildup and when I flew into the second updraft the aircraft failed to respond to my nose down, fwd, SS input for a couple of seconds. I assumed at the time that the updraft caused a "g" loading that fooled the ELAC. The buildup was small and we flew out of it in a few short seconds.


Regarding my mentioned experience where a A319 did not respond to a nose down SS input: for the brief moment I was in an updraft, the nose did not follow the input - once I flew out of the updraft the nose came down and we continued as if nothing had happened......... Knowing that pitch is load factor demand, and being in a updraft/downdraft/updraft/downdraft situation, and considering that the nose came down as soon as I passed the building cumulus, and considering that the Bus behaved normally the rest of the flight, I chalked it up to being in an Airbus. To me, it was no different than waiting for the MCDU to finish "updating" the page. Airbus pilots will know what I'm talking about.

Sorry Clandestino, but you're being overly dramatic. No report was made because none was necessary.

I still don't get it. You are trying to jump over towering cumulus by trading as much speed for altitude as possible - "green dot" is very technical term for minimum clean speed. You fail to clear TCU. You hit the updraft and lose downward pitch authority. And yet, you think it is normal aeroplane behaviour.

Congratulations on your coolness but I fail to understand source of it. Why would you think it is normal to loose downward pitch authority? Was it something in your training? Did you experience it many times? Why do you assume that what's valid for navigation system is also valid for flight controls system? Could you please explain how updraft can fool ELAC into robbing you of nosedown authority?

Maybe this message is not exactly « technical » enough for the Tech logNot at all, it fits perfectly into this thread.

They told me that they learnt from that accident a lot of things they certainly did not know at the time.All of us did. AF447 has gone where no 330 has gone before. Unsurprisingly, there were many surprises to be found there.

Facts that are well known to test pilots or military fighter pilots, but which you have no way to learn in a career where you start at nearly zero experience on the A320 and end on the A380.Unless your interest in aviation does not end at what is legally required, that is.

you move the controls to a position that you think useful…or that the airplane manufacturer recommendsWhat matters is whether what you do recovers you to normal flight and manufacturers are betting their reputation and existence on their procedures being best available. There was procedure for dealing with unreliable airspeed. There was procedure for approach to stall. None was followed. It would be terrible waste if all we can learn from AF 447 is "Don't pull when faced with stall warning"

For example, when in an unusual position, a stall, a spin, you move the controls to a position that you think useful…or that the airplane manufacturer recommends,and you wait. You wait for long seconds, until the new position of the flight controls gives a result. Then, eventually, you wait some more…Many airline pilots have never practised that, and have no knowledge of it. I am not surprised at all, since what you wrote is only applicable for spin recovery in some types with less than savoury spin characteristic. If in unusual attitude and not stalled, you do not wait for controls to take effect. They might be mushy or ineffective (EDIT: I should have written "stiff" instead of "ineffective", sorry about the lapsus) but effect will be pretty quick - powered controls lag notwithstanding. Aeroplane that doesn't reply to controls is certain signal of some deeper trouble, be it stall, ice, control failure or airframe failure.

Personally, I am more than little amused by all the exaltations about airline pilots needing full stall recovery training. Ones pleading for it might be correct but let it remain type specific, please. I have just passed 4000 hours mark on aeroplanes that would simply kill me if I ever stall them. Don't see anyone being too excited about it, though.

forget it, nobody knew anything about it Is it OK if they just knew the FCOM chapter where they could read about it?

experts are now considering a pitch-up into the deep stall never encountered in flight testingWhy? Wasn't pitch up flight controls and thrust induced?

I think that we should keep in mind the very scant knowledge and training of the pilots at the time in the aerodynamics, stall recovery techniques, stall recognition…It was NEVER thought at the time that those planes could fly beyond the « approach to stall ». It was never thought either that the plane could « fly » with 40 degrees AOA and only 8 or 10 degrees of nose up.

So, of course the crew might have done better, but they certainly were not seriously prepared for what happened. May they rest in peace. Totally agree. Not necessarily for the same reasons.

[Organfreak]

Clandestino wrote:
There was procedure for approach to stall. None was followed.

What, to gun it and pull up? Ha!
No, not at high altitude, there wasn't. Stall training, as I read it, was only for low-altitude problems such as wind-shear. This was one of the shockers :eek: to come out of the reports, so far. Somebody please set me straight if I have misunderstood.

Personally, I am more than little amused by all the exaltations about airline pilots needing full stall recovery training. Ones pleading for it might be correct but let it remain type specific, please.

Yikes! OK, type-specific: I will never, ever, fly in a 'Bus again until I am sure that everybody holding my life in their hands is properly trained for such rare and unusual attitudes. Passengers do not expect to gamble on such things. In fact, I'm sure there are 228 souls who would emphatically disagree. :cool:

[AlphaZuluRomeo]

The problem (as you state below regarding another point, and as I think I said in my original reply) is with false positives.
Well, what would be a pilot's choice. I ask the question:
Pilots, do you prefer:
a] an aircraft that may (auto)trim nose up when it's (near) stalled
b] an aircraft that may not (auto)trim nose up when such trim is good, because the said aircraft suffers a "failure" with AoA measurement?
My (unqualified) answer is that 'a' seems more dangerous than 'b'. Then I choose 'b'.

About complexity: Yes, such a feature would add one more logical test. See airtren's post - it's a lot more involved than that, going right back to the specification and trying to define potential knock-on effects of the change.
Dozy, I'm not trying to describe what it takes to implement a feature, I'm limiting myself on the "logical sheme", as I think this is all what is of interest to airmen (I can be wrong, there, and stand to be corrected).
So basically, I was agreeing to what you said: yes, one more "test" to do before allowing the autotrim to do its job is adding complexity to the system.
Having by no mean done any of a serious study (from a manufacturer perspective) on such an implementation, I won't comment on the "how much more complexity".

The protections are a separate subsystem entirely from the annunciation/warning subsystem. There is no overarching logic connecting them, which makes implementing such a change considerably harder.
Huh? What's the point? Are you saying that:
- inhibiting NU autotrim when a protection is ON
is far more simple than
- inhibiting NU autotrim when a warning is ON
??
I don't understand. Protection and warning share a source: The actual AoA. I don't see where is the "more complex/difficult" thing.
By the way, IIRC (*) on the A310 (older system), there is no "hard" protection. But when the aircraft "senses" a too large AoA, I believe it enters a specific mode which "unwind" the trim by x degrees.
(*) Ref is an east-european A310 (TAROM?) incident on approach to ORY, years back.


I can see where you're coming from, I just think that a hard limit on autotrim under certain flight control circumstances would make more sense.
I'm not sure to follow you, there. Could you elaborate, please?


With an eager and switched-on crew, sure that'd work. But this crew in the wee hours appeared not to notice a Stall Warning that was blaring in their ears for nearly a minute. By the time the AoA values became invalid, the situation was pretty grim - what chance they'd notice the warning you suggest?
I don't know why AF447 crew didn't react to the S/W. If we assume they "fail to notice it", then no, the warning I suggest would probably not have had any use. Except, perhaps, with the CPT who returned just ~ the time the S/W came OFF...



I think that design decision is a compromise - i.e. after an abnormal situation like that, would the crew notice that FDs were available and switch them back on again? I think the idea there was that they'd bring the FD back once the data was good, it would then be up to the crew to either use, disregard or disable them.
Yep. Would like to know what pilots would prefer?

[AlphaZuluRomeo]

Clandestino wrote:
There was procedure for approach to stall. None was followed.

What, to gun it and pull up? Ha!
No, not at high altitude, there wasn't. Stall training, as I read it, was only for low-altitude problems such as wind-shear. This was one of the shockers :eek: to come out of the reports, so far. Somebody please set me straight if I have misunderstood.
I'm afraid you misunderstood.
Ref to interim report #2, where the AF procedure "stall warning" (at the time of the accident) is reproduced.
Abstract:
During any other flight phases after lift-off:
- TOGA
- Reduce pitch attitude
- Wings level
- Retract speed brakes.

Is that really "to gun it and pull up"?

I agree with you on the "no-training" part (high altitude), but Clandestino wrote "There was procedure", not "There was training". ;)

[BOAC]

Personally I would like to be handed a basic aeroplane, but that is probably because I am so old I can fly one.:)

Way back I attributed to DW (but he said 'not me') the concept of the AB software reverting to Direct Law on such a failure as 447 had. IF then crews know this, they can be (hopefully) given the training to actually fly a real aeroplane. If they were, for example, to need trim, as long as there is some way they can INPUT it themselves - as required - that's fine. I would not wish some *** (censored for DW's peace of mind) to decide to put it in for me. I would, after all, know I need it, because I am a pilot. I should then know I have done it (because I am a pilot) if it becomes troublesome, whereas it is more than possible that the unfortunate 447 PF had NO idea he had full nose up HS - as I think the PGF PF also did not. KISS?

I just cannot see the problem- computers go tits up - pilots get given a machine that will fly the old fashioned way - all the bells and whistles are absent - who cares? It's an emergency. We don't need them.

[CONF iture]

or if the limit applied to autotrim only, forcing pilots who are not used to trimming manually to do so at altitude with an abnormal situation on their hands.
When a concept atrophies a pilot's basic ability such as trimming, there are very serious questions to be asked regarding that design, especially as that pilot could be requested to instantaneously master that art again following a malfunction of that very same wonder concept.


But I would like to hear you about that one first :
So Dozy, how do you explain the AOA inhibit of nose up trim in Normal Law? Why did the engineers decide that was sensible?

[jcjeant]

Hi,

When a concept atrophies a pilot's basic ability such as trimming, there are very serious questions to be asked regarding that design, especially as that pilot could be requested to instantaneously master that art again following a malfunction of that very same wonder concept.Those kind of consequences (atrophy of basic skills by a concept) is coming common in the industry
I see that in marine industry (unable to control manually water level and pressure of a high press steam boiler)
Again ..training .. training .. it's must be trained .. as the marine engineers who have the experience to manually control a boiler are a endangered specie !!
Even manually coupling on the electrical bus bars one diesel generator is for someone a unknow task !

[airtren]

See airtren's post - it's a lot more involved than that, going right back to the specification and trying to define potential knock-on effects of the change.

Having by no mean done any of a serious study (from a manufacturer perspective) on such an implementation, I won't comment on the "how much more complexity".

Here is what needs be known:

The algorithm change is minimal - adding one test - and brings the Alternate Law "autotrim" behavior to be similar to the Normal Law "autotrim" behavior, so it's NOT something completely new.
The additional test in the algorithm requires a version upgrade in a number of internal specifications, that are documenting that algorithm, and in the user documents. The algorithm change is followed by a change of the software implementation, which depending of programming language goes from a line or two - the additional test - in high level language, to perhaps about 6-10 instructions, in machine language.

Is that a lot? That's about as minimal as one would get in terms of a software fix/upgrade.

A software upgrade is the easiest change, a lot easier than changing hardware, mechanical, hydraulic, etc.. components

[Lonewolf_50]

Dozy:
On the line or when training?
Both.
But for me "on line" was flying in the Navy, not hauling hundreds of folks about the skies to Rio and Venice and Bali and other nice places. A half dozen souls at a time were all who were at risk were I to cock it all up.

Lyman:

You misunderstand my "how CRM is supposed to work" scenario. As we have noted previously (three or four threads ago), is was not how the cockpit discussion went based on what BEA has released to us. I was using a general conversation, not trying to repeat verbatim what was actuall recorded.

OK?

CRM in that cockpit: from the evidence provided, it was not up to scratch beginning about ten to fifteen seconds after the UAS incident began ...

[RetiredF4]

All bolding by me

DozyWannabe
But this crew in the wee hours appeared not to notice a Stall Warning that was blaring in their ears for nearly a minute. By the time the AoA values became invalid, the situation was pretty grim - what chance they'd notice the warning you suggest?

Was the stall warning not noticed, noticed but not formally announced, noticed and not formally announced and not successfully reacted upon?


Let´s look at BEA Interim report 3: (bolding by me)

BEA IR3 Page 74 3rd para
At 2 h 10 min 10, the PF’s nose-up inputs increased the angle of attack and the stall warning triggered twice transitorily. Probably in reaction to this warning, the PNF exclaimed “what is that?” .

BEA IR3 P75 6th para
At 2 h 10 min 51, ........... Five seconds later, probably in reaction to the stall warning, the PF pushed the thrust levers towards the TO/GA detent and called it out. It was at about that time that the airplane exited its flight envelope.

BEA IR3 P 76 1st para
A little after 2 h 11 min 30, the PF said twice that he had lost control of the airplane.

BEA IR3 page 76 3rd para
At around 2 h 11 min 42, the Captain came back into the cockpit, a very short time before the stall warning stopped. ........ Neither of the two copilots gave him a precise summary of the problems encountered nor of the actions undertaken, except that they had lost control of the airplane and that they had tried everything.

BEA assumes, that both stall warnings had been recognized and honoured by an action (although not successfull ones), and the PF admitted twice and the PF and PNF stated to the captain, that they had lost control of the aircraft, which could be a term to describe the fallout of the stalled situation.

BEA IR3 page 76 7th para
At around 2 h 11 min 42, the Captain came back into the cockpit, a very short time before the stall warning stopped...................Neither of the two copilots formally identified the stall situation that the airplane was in, either via the aural warning, or by recognising the buffet, or by interpreting the high vertical speed and pitch attitude values. It should be noted that buffet is the only indication of the approach to stall at high altitude on other airplanes whose stall warning threshold does not vary with the Mach.

We have to consider that BEA had made up its mind concerning this issue. The crew probably reacted to the stall warnings and admitted to have lost control, but did not formally announce stall to each other and also not to the captain.

DozyWannabe (bolding by me for reference)
We know the ADI on the LHS was OK from the DFDR, and the ISIS seems to have been OK too, otherwise the Captain would not have pointed it out.

BEA IR3 P76 3rd para
Neither of the two copilots gave him a precise summary of the problems encountered nor of the actions undertaken, except that they had lost control of the airplane and that they had tried everything. In reaction, the Captain said several times “take that”, doubtless speaking of the FPV (time 02:12:52

I could not find your claim, that the captain was pointing to the ISIS, but i might have overlooked it in the report. Can you point me to it?

Edit: Thank you DW, found it with your help!

The following two quotes are for the one / ones, who still think(s) that instruments tell it all.

BEA IR3 P 76 8th para
In the absence of relevant information from the copilots, reading the information available on the screens (pitch attitude, roll, thrust, vertical speed, altitude, etc…) was not sufficient in itself for the Captain to become rapidly aware of the airplane’s situation. He did not then ask questions that could have helped him to understand the sequence of events.

Some say, he would have understood better without asking, if he would have been able to observe a full NU control input together with the instruments.

BEA IR3 P 76 last para
Despite several references to the altitude, which was falling, none of the three crew members seemed to be able to determine which information to rely on: for them, the pitch attitude, rolland thrust values could seem inconsistent with the vertical speed and altitude values.

And that one for the audio channel:
BEA IR3 P76 9th para
The stall warning lasted 54 seconds continuously, during which time neither of the copilots made any reference to it. It is likely that the Captain heard this warning a few moments before coming back into the cockpit, but it is also likely that the multiple starts and stops added to the confusion and disturbed his diagnosis of the situation.

franzl

[DozyWannabe]

Here is what needs be known:

The algorithm change is minimal - adding one test - and brings the Alternate Law "autotrim" behavior to be similar to the Normal Law "autotrim" behavior, so it's NOT something completely new.

You don't know that - the change itself may be minor, but the surrounding modules must all be tested to make sure there are no adverse effects. The development process is considerably different to any other software development methodology - even other real-time systems.

If you don't believe me, let my late Prof. explain:

Report on visit to Airbus Industrie - 28-29th Jan. 1993 (http://www.kls2.com/cgi-bin/arcfetch?db=sci.aeronautics.airliners&id=%[email protected]%3E)

I could not find your claim, that the captain was pointing to the ISIS, but i might have overlooked it in the report. Can you point me to it?

(Emphasis mine)


02:12:19 - 02:12:45:
PF : That’s good we should be wings level, no it won’t (not)
CDB : The wings to flat horizon the standby horizon
PNF : The horizon (second)


In the middle of the intermittent stall warnings is when the PF makes his comment "I have the impression that we have some crazy speed no what do you think?", which we're told by some of our French posters refers to the PF believing they were in overspeed. The Stall Warning comes on again shortly after he makes that statement, so either he's not hearing it, or he has ruled it out as erroneous.

[CONF iture]

I don't know why the A320 sim limits the nose-up trim and the A330 didn't in this case. Someone suggested that the limit might be airspeed-dependent, but the TRE had failed both ADCs.
Still one ADR ... no ?

[airtren]

You don't know that - the change itself may be minor, but the surrounding modules must all be tested to make sure there are no adverse effects. The development process is considerably different to any other software development methodology - even other real-time systems.

Testing is part of an upgrade, and it is proportional in all aspects to the type of system, and the type of manufacturer. Don't get into assumptions territory with my knowledge base, and let's keep things at their real scale and/or proportions. It's up to Airbus to have a clean, efficient, straight forward process, or a complicated mess. It is expected that theirs is not bellow - actually it could be very well above - the level that is considered norm in such type of critical systems - appropriate level of automation/simulation, etc.. .

[CONF iture]

Something is not clear with the STALL WARNING :

For the 330 the FCOM mentions there is no FLT PHASE INHIB.
In the meantime there is an EMERGENCY PROCEDURE called STALL WARNING AT LIFT-OFF when such warning may sound if an AoA probe is damaged. I would then think there is actually an inhibit as long as there is still WOW ...

For the 320 the FCOM (not updated) clearly mentions that the STALL WRN in inhibited on GND.

I see no logic behind the logic as described on page 20 in report #3 :
If the CAS measurements for the three ADR are lower than 60 kt, the angle of attack values of the three ADR are invalid (NCD status) and the stall warning is then inoperative. This results from a logic stating that the airflow must be sufficient to ensure a valid measurement by the angle of attack sensors, especially to prevent spurious warnings on the ground.

[infrequentflyer789]

It was implied that testing is done, and it is proportional in all aspects to the type of system, and the type of manufacturer. Please don't make assumptions what I know or don't, and let's keep things at their real scale and proportions. I think it is expected that Airbus is not bellow - actually it could be very well above - the level that is considered norm in such type of critical systems, and the testing is sophisticated, with extensive automation/simulation.

I'd agree with that, but the tak might not be as simple as presented.

We are talking about taking a single protection active in one law/mode and making it available in another mode. In the other mode that protection is part of a set, and the algortihms and code may well be interdependent, so you have to first split out the logic for that one protection and that might not be simple. Setting up the testing etc. won't be as simple either, for the same reason.

Further, it's entirely possible that the air data you need for the protection is simply not available at the flight control computers (prim or sec) in the event of airdata failure. I'm basing that on two things - the non-switch to abnormal-attitute law in 447 (which should have tripped on AOA, but didn't because of triple AD failure) and the reports that the BUSS option requires new airdata units in order to route raw AOA data around the ADIRU. Even if you could base your new code off the BUSS option, that still makes it a non-trivial hardware change rather than just a software patch, and you've also probably got to get an additional input ("raw" AOA) into the flight computers - maybe more hardware change and definitely much more testing.


However, I think there may be an even bigger problem that is much more fundamental. Looking across the civilian FBW implementations, there is a clear and consistent decision that protections/limits based on airdata are dropped when airdata is not valid/trusted. Either that is an independent engineering decision across teams/types and mfrs (yes, it's the same on B), or it's a regulatory / certification decision.

You need to overturn that decision to put trim protections into Alt2.

Bear in mind that if/when you do, a line has been crossed. Currently with UAS or other airdata failure, a good crew that can
a) work out which instruments they can trust
b) fly the plane within the safe envelope based on (a)
will survive. Throw in protections based on partial/incomplete/known-bad airdata and sooner or later you will kill a good crew that's doing the right thing. [There is still a chance of that in normal law, but it's much lower and much easier to quantify and try to design out. You couldn't even simulate all the failure modes for the input data for the bad airdata case].

So, who do you want to kill ? - because that is what it boils down to. It's normally the engineers faced with the dilema, maybe it should be answered by the pilots ?

[infrequentflyer789]

Something is not clear with the STALL WARNING :
[...]
I see no logic behind the logic as described on page 20 in report #3 :

Possibly belt and braces - WOW switches not sufficiently reliable on their own (not a great history of reliability, and they regularly take a beating in use).

There may be more behind it than just SW as well. Active protections have consequences requiring greater data certainty than mere warnings. SW on taxiway is one thing, alpha-floor on taxiway likely to end less well...

For what it's worth, I think we may see this logic changed - if it's in software and is an easy update. If it's hardware and needs 3xADIRU replaced I think it's somewhat less likely....

[CONF iture]

IF789,
I think you put things far more complicated that they need to be :

When there is a known problem on the data or one is suspected, just stop the Magic and reverse to the conventional aircraft in Direct Law.

Did you say KISS (http://www.pprune.org/6809130-post289.html) BOAC ?

[CONF iture]

WOW switches not sufficiently reliable on their own (not a great history of reliability, and they regularly take a beating in use).
Then why is it good enough for the 320 ?

[AlphaZuluRomeo]

IF789,
I think you put things far more complicated that they need to be :

When there is a known problem on the data or one is suspected, just stop the Magic and reverse to the conventional aircraft in Direct Law.

Did you say KISS (http://www.pprune.org/6809130-post289.html) BOAC ?

That would be far more simple, indeed:
- for the engineering team to implement
- for the pilots to "understand"

Now, Airbus made a different "philosophical" choice. "Why" is a good question.
A guess: Alternate law retains "parts of" automation. What would we say if there was an accident and we found out that the accident could have been prevented by a protection/automation that was made inop because of a reversion to direct law, while the input data needed for this protection were available & reliable.
Exemple : Let's imagine AF447, the aircraft stalls but then the crew engage a recovery : nose down, AoA is lessened, speed come back. At this point, the PF pulls on his stick to go back to level flight but he pulls too hard.
If reversion to direct law => overstressed the plane => structural failure => irrecoverrable => crash.
If reversion to alternate law => g protection still available => no overstress => plane recovers => continue flight => lands with all souls onboard alive.

See the point? That's about "graceful degradation" if I understand the concept correctly.

[airtren]

We are talking about taking a single protection active in one law/mode and making it available in another mode. In the other mode that protection is part of a set, and the algortihms and code may well be interdependent, so you have to first split out the logic for that one protection and that might not be simple. Setting up the testing etc. won't be as simple either, for the same reason.
I read your "may" as your making a cautious assumption, which is always welcome at the outset. A closer perspective can clarify if the more distant perspective caution is justified.

With the risk of repeating the considerations mentioned by AlphaZuluRomeo, with my own closer perspective and words:

As far as I can remember from when I looked closely at Normal Law protections, in an up-down sequential flow, the elements of the set are parallel, and independent.

Please note, dependency of more than one algorithm on a certain parameter, which, if I recall correctly is the case, does not make the elements of the set of algorithms dependent on each other, or interspersed.

An additional factor is that the Alternate Law is a subset of Normal Law, in fact a minimal subset, which means that the number of parallel algorithms in the set is minimal.

These are both elements that speak about simplicity.

...
However, I think there may be an even bigger problem that is much more fundamental. Looking across the civilian FBW implementations, there is a clear and consistent decision that protections/limits based on airdata are dropped when airdata is not valid/trusted. Either that is an independent engineering decision across teams/types and mfrs (yes, it's the same on B), or it's a regulatory / certification decision.

You need to overturn that decision to put trim protections into Alt2.
It's good to remind us the philosophical and general principles, if there is a suspicion that the "higher" perspective was lost.

But I don't think it was the case, the perspective was/is there.

In the same time let's not loose the close perspective - while we look at the Forest, let's keep looking at the Tree we're concerned about.

The function of the Autotrim is an automation factor to "the Trimmed Stabilizer".

When Autotrim didn't exist, pilots did the trimming Manually - if the "trimmed stabilizer" was present - if there was no "trimmed stabilizer" on a plane, the pilot did NO trimming at all

So, the intention of the "automation" was/is to do the "autotrim", on behalf of the pilot, in those conditions in which the pilot would have done the "manual trimming". This is very important and should be remembered by everyone, pilots, engineers, system architects, managers,etc.... !

What do we have in the AF447 case?

We have the STALL condition being announced loudly - and after so much analysis, very clear in its meaning to us - and throughout the duration of that announcement, we have an "automation" decision/action of employing the "autotrim" to max NU, which obviously if it did anything, it helped the STALL.


So, who do you want to kill ? - because that is what it boils down to. It's normally the engineers faced with the dilema, maybe it should be answered by the pilots ?The analysis work of last 2 years, performed by appropriate organizations, and the very clear and loud resulting recommendations for the required actions from pilots at High Altitude Stall Approach, or Stall is to bring the ND, which implies the strong recommendation of NO Manual Trimming NU during such conditions!

When remembering the few lines above, that the "automation"s role is to only do what the pilot would do manually if automation was not present, the answer to anyone's dilemma seems simple....extend the "don't do manual trim NU", with "don't do manual/automated trim NU"...

IMO, the recommendations for what "automation" is supposed to do during the conditions of the new recommendations for pilots are just one step behind. The lag seems to be normal, although the current dichotomy
present in some systems will need be resolved regardless of recommendations or not.

[Dani]

It's a big misconception that there is alternate law in Airbus fbw software. Of course we call it alternate, but what it basically is is a degradation of normal law. There is only normal and direct law, and the intermediate position where one degree of freedom still is in normal and the other not anymore is called alternate.

The more protection you lose, the closer you get to direct law. You could now design three dozens of different laws, a gradual sinking into direct law. To make it more easily, they invented 3 positions, which makes absolutely sense to me.

I said it and I say it once more: You as a pilot don't have to know in which law you are. There is no ECAM message "YOU ARE IN XXX LAW". You can fly the aircraft in any law. Just where the amber x's are, that's where you lost your protections.

Now you laugh at me and say "if they (AF447) would have been in normal law, the aircraft never fell into stall". This might be right. But as a wise pilot you just don't pull these maneuvers, even if you can (in normal law). "It is possible in normal law" is no excuse for behaving like an imbecile.

[airtren]

It's a big misconception that there is alternate law in Airbus fbw software. Of course we call it alternate, but what it basically is is a degradation of normal law. There is only normal and alternate law, and the intermediate position where one degree of freedom still is in normal and the other not anymore is called alternate.

A common main path, versus different main paths is not really relevant. That's because a common path implies branching separate ways into separate sub-paths depending on Law, when decisions and outputs are specific and different for each Law, which ultimately is sort of equivalent. This type of sub-path, which be then the object of the considerations made in this discussion, is still technically a different path, even if a short one. In cases when outputs are similar, the branching/separation may be followed by a rejoining a common path.

The more protection you lose, the closer you get to normal law.Huh? Do I misread this, or is a typo?

The more protections you lose the closer you are to direct law.

[Dani]

Sorry, wrote it in a hurry, but you are right. Of course these are new branches, and software engineers think like that. I have nothing against it. I just want to help non software engineers to think correctly. Pilots get confused when showing too much complexity. They like it simple (anyone said KISS? ;) ), because in the air and under stress you lose your ability to think in details.

When an outstander, which most of the contributers here are, hears about all this laws, he thinks: How could they have made it so complicated. It isn't complicated. Just think straight, think KISS, and Airbus is KISS.

[airtren]

....

When an outstander, which most of the contributers here are, hears about all this laws, he thinks: How could they have made it so complicated. It isn't complicated. Just think straight, think KISS, and Airbus is KISS.

For one understanding them well, they're simple - you're right

Interestingly, that applies also to algorithms and their implementation :O

Pilots get confused when showing too much complexity. They like it simple (anyone said KISS? http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/wink2.gif ), because in the air and under stress you lose your ability to think in detailsThis is a very good additional argument of why the SS (under PF control) should be placed so that it can be seen - under stress, the visual contact with the SS, is the easiest way to know what's going on with it.

[CONF iture]

There is no ECAM message "YOU ARE IN XXX LAW"
Of course there are :

F/CTL ALTN LAW
F/CTL DIRECT LAW


Airbus is so KISS when manually flying that he trims for you ... but sometimes he does not. When he does not he supposed to advise you but it appears he may forget as well.

"It is possible in normal law" is no excuse for behaving like an imbecile.
Don't rush your judgement as you rush your writing.

[DozyWannabe]

Airbus is so KISS when manually flying that he trims for you ... but sometimes he does not. When he does not he supposed to advise you but it appears he may forget as well.

Doesn't a drop to Direct Law have an amber "USE MAN PITCH TRIM" annunciation?

[Organfreak]

Dozy:
Doesn't a drop to Direct Law have an amber "USE MAN PITCH TRIM" annunciation?

Yup.

[CONF iture]

But disappears in Abnormal Attitudes Law
BEA pretends Altn Law was the active Law all the way


What I can report from my own experiment in the sim :

I could not get a fwd autotrim
But USE MAN PITCH TRIM FLAG was NOT displayed on the PFD

[Dani]

CONFiture:

But disappears in Abnormal Attitudes Law

it doesn't disappear, it never appears.

BEA pretends Altn Law was the active Law all the way

I do not doubt this. Imagine: No valid speed, therefor several fault messages from/through ADR.

I could not get a fwd autotrim

Which is confirmed by FCOM. The aircraft behaves like they say it does.

But USE MAN PITCH TRIM FLAG was NOT displayed on the PFD

This message appears in direct law, not in alternate law.

The only way you can tell that you are in alternate law is (apart from ECAM messages, thanks for the correction) are the amber crosses on PFD.

Dani

[Lyman]

What you seem to be missing, perhaps, philosophically, is the aircraft is mimicking the actual degradation of the suite of cues, displays, and controls that are the very genesis of the LAW degrade in the first place.

When, for any reason, cues and behaviour of airframe are lost to the holes in the cheese, how beneficial is it for the a/c to do the same? Fair enough, this is true for Direct DIRECT also. However, once in DIRECT, the skillset is less chsallenged, the a/c becomes a simple machine, not an automatic one. The interface is straightforward, and quickly acquired. At this point, airmanship is the key, not the interface that mimics it.

To change the response and controls automatically, requires an additional workload, and from my perspective, a most unwelcome one. Looking out the telescope frrom the small end, (what we are doing here), is easy, and without stress or penalty.

Looking through the telescope in reverse, (what the crew were doing), does not form a large enough background for global view. When the flying gets complex, why add additional changes that may cause consternation to a hyperfocused crew, looking for the ONE thing that needs the most attention? Simplification is the driving force, or should be.

The bottom line is the additional workload. Unwelcome, says I.

Right, Wrong, or Indifferent, the crew were unable to isolate the simplest move, get the Nose Down.

The confusion came from somewhere, I say a fair portion of it came from the platform. Fair?

[CONF iture]

Perpignan told a different story as the USE MAN PITCH TRIM FLAG was initially displayed but disappeared when the flight switched into Abnormal Attitudes Law.

Dani, what is that FCOM reference that could explain I was not able to get a forward autotrim ?

[Old Carthusian]

I rather think that it would not be a fair attribution to suspect the platform. The factor that might best describe what you're driving at would be 'Know your machine' which is a training and cultural issue. We have no evidence of a chain of command, CRM or use of standard procedures. Given that all of these seem lacking any platform is going to produce a similar result in similar circumstances.

[DozyWannabe]

Dani, what is that FCOM reference that could explain I was not able to get a forward autotrim ?

And yet on the A320 sim I did. Have you tried talking to the sim engineers about that one?

Thus far there have been no emergency fixes released for the A330 in terms of hardware or software, but there has been a new stall recovery procedure which instructs use of the sidestick to push the nose down. This suggests to me that Airbus and the BEA got positive autotrim response when they tried it on their A330 sim.

[Lyman]

Not only that, but the MEMO, when released by BEA, provided no NEW MECHANICAL issues that hadn't been addressed....We don't go there....

OC... It isn't that black and white. There are four degradations that can obtain post UAS. ALT1, ALT2, DIRECT, and ABNORMAL. PITCH and POWER are nothing if not offspring of MANUAL, why present one or more of these different concepts when ostensibly, P/P is always the Drill? P/P is successful, or it is not, and if not, protection memory accomplishes what? Protections obtain when the pilot has lost control anyway? Why bother with stops along the way to DIRECT (PITCH AND POWER)? Did the a/c linger in NORMAL whilst P/P could be applied? If not, why not? And if inertials were such the hot ticket, why not blacken both PFDS in favor of an ISIS with reads in RED?

Complexity for the sake of......?

Another thought. Why leave NORMAL LAW at all? It is possible for NORMAL to retain, even with a/p loss. Just not with unreliable speeds.

[Old Carthusian]

OC... It isn't that black and white. There are four degradations that can obtain post UAS. ALT1, ALT2, DIRECT, and ABNORMAL. PITCH and POWER are nothing if not offspring of MANUAL, why present one or more of these different concepts when ostensibly, P/P is always the Drill?

It would still come down to training wouldn't it? Me, I'm no Airbus pilot but those who post on this board seem to have no problems with the system as configured. One can legitimately argue that it can be improved but then so can everything. It's logical and it works so I would be very leery of attributing any causal factors to it. The issue is really the inability to analyse the UAS correctly and the unexplained stick movements by the PF (we all have our suspicions but we can't be certain). I would agree that P/P is the drill but if you don't get your initial analysis right then it becomes rather moot.

[infrequentflyer789]

I read your "may" as your making a cautious assumption, which is always welcome at the outset. A closer perspective can clarify if the more distant perspective caution is justified.


You're right, but it's also a general statement of the need to be cautious about what is or is not "simple" in software without detailed knowledge. A fair few years in software development has taught me that it's very easy for someone to believe they know enough about the internals of a system to assess the impact of a change request, when in fact they don't. Dependencies can be very subtle. Often the CR will eventually (sometimes only after the test start failing or the user bug reports start landing) hit the desk of the person that does understand the impact and result in an expletive laden exclamation about how that change could obviously never be done without a major redesign...

Unless you've actually worked with and modified (not just read) the actual code, I would always advise that caution. Sometimes I might even follow that advice myself ;) .



With the risk of repeating the considerations mentioned by AlphaZuluRomeo, with my own closer perspective and words:
Be interested if you know whether or not there would be a change required for getting AOA into the FCPC around the ADIRU in the event of ADIRU going "failed".


We have the STALL condition being announced loudly
Stall [I]warning.


at High Altitude Stall Approach, or Stall is to bring the ND, which implies the strong recommendation of NO Manual Trimming NU during such conditions!
And therein lies the dillema - warning vs actual conditions. Maybe I didn't expalin well.

If the 'bus flight control is in a mode where it is confident that stall condition is anywhere near, it will take action to prevent it (over and above trim limits). Normal law.

If it has lost confidence (e.g. airdata fail) about its condition but has indication that it might be stalling, it will warn the real pilots, but not take overriding action. The pilots can then use actual intelligence (of which the machine has none) to assess the warning and the condition of the a/c and take action. Worth looking at Perpignan report for another example of the difference (dual aoa failure, outlier aoa not trusted for protection but used for warning).

In this case, 447, the warning was actually right, and the pilots assessment fatally wrong.

Change it so the FCC will act and "protect" in the warning scenario based on known-bad data, then you might save 447. At the same time, you risk the warning being wrong (due to bad data), the pilot assessment and actions being correct, and the a/c "protecting" them into the ground...

I think the risks either way are going to be very very difficult to quantify which is why this is a tough call.

[CONF iture]

And yet on the A320 sim I did. Have you tried talking to the sim engineers about that one?
Your A320 sim didn't trim up under STALL WRN, and yet my A330 sim did ... as also AF447.

Thus far there have been no emergency fixes released for the A330 in terms of hardware or software, but there has been a new stall recovery procedure which instructs use of the sidestick to push the nose down. This suggests to me that Airbus and the BEA got positive autotrim response when they tried it on their A330 sim.
And we have Jacques Rosay, Airbus VP Chief Test Pilot, who states :
In certain cases, an action in the same direction on the longitudinal trim may be needed.

[infrequentflyer789]

Perpignan told a different story as the USE MAN PITCH TRIM FLAG was initially displayed but disappeared when the flight switched into Abnormal Attitudes Law.

Dani, what is that FCOM reference that could explain I was not able to get a forward autotrim ?

Did it disappear by law change or just get pushed out of view by other ecam messages ? Same effect, different reason. .

FCOM reference - section on abnormal attitude flight law. But you know that :)

The real issue is how you went into that law in sim, but DW didn't and 447 didn't.

Based on what I've read:


447 stayed in Alt2 because triple ADR failure meant it wouldn't switch based on airdata conditions (and g-load conditions weren't breached).
Your sim went into abnormal law based on AOA following dual (not triple) ADR fail
DW sim again not triple ADR failure, but I'm not sure AOA got high enough to trigger abnormal law from what he's written.

Now, can anyone provide FCOM reference for the triple adr fail caveat on abnormal law entry conditions.... I don't think it's in there.

And yes, not having "use man pitch trim" displayed in abnormal law is not logical to me either. In fact, I'm not sure why abnormal law is there at all - can't see why not use direct law for this purpose (abnormal attitude recovery). What extra authority does abnormal law give over direct ?

[I]

[TTex600]

I still don't get it. You are trying to jump over towering cumulus by trading as much speed for altitude as possible - "green dot" is very technical term for minimum clean speed. You fail to clear TCU. You hit the updraft and lose downward pitch authority. And yet, you think it is normal aeroplane behaviour.

Congratulations on your coolness but I fail to understand source of it. Why would you think it is normal to loose downward pitch authority? Was it something in your training? Did you experience it many times? Why do you assume that what's valid for navigation system is also valid for flight controls system? Could you please explain how updraft can fool ELAC into robbing you of nosedown authority?

I have just passed 4000 hours mark on aeroplanes that would simply kill me if I ever stall them. Don't see anyone being too excited about it,

Green dot is not minimum clean speed. Green dot is L/D max. Considering this basic point, I fail to find it worth my time to further discuss this, or the AB with you.

Because you bring experience into the discussion, I've well more than three times the time you mention and have never NOT flown an aircraft that could simply kill me if I stalled them. But then again, I've intentionally stalled many a DC9 and am still here to tell the tale. Good day.

[Machinbird]

I think the risks either way are going to be very very difficult to quantify which is why this is a tough call. That is what the engineers get their pay for...making tough decisions on system design.:}

I don't design circuits for a living or write software, but I've done a fair amount of root cause analysis on defective equipment and have had pretty good exposure to same over the last 55 years. The following is a gut feeling hypothesis only so take it with a healthy dose of skepticism:

Once all 3 airspeeds become corrupted from high AOA, if any part of the primary or supporting calculations for operation of the trim rely on airspeed or its derivatives, then operation of the trim becomes compromised. Without looking at an actual complete logic diagram of how the system operates, this is difficult to analyze.. Something as mundane as a calculation of how much torque the hydraulic drive motors must generate to drive the THS (just for example) can have airspeed components in it that crash the whole logic chain for THS drive. Any reasonable software would then have error handling options for such an error. Generally the safest option would be to halt all automatic motion on error.

Now I could be seriously wrong here, but something stopped the THS from trimming nose up before it actually hit the end limits. If it was an error handling routine, it might stop nose down trim as well until some reliable airspeed information appeared. In this case you might effectively be in "Direct Law" without an indication, at least as far as THS trim goes. Elevator motion would then still be Alt2 though.

[Zorin_75]

Machinbird,

without getting into the realism of your ideas - during their whole descent, they never even got to down elevator, so nothing weird is needed for the ths not to move...

[Machinbird]

Machinbird,
without getting into the realism of your ideas - during their whole descent, they never even got to down elevator, so nothing weird is needed for the ths not to move...
Yes, the elevator never made it past neutral, but that mayonaise stirring stick did for a large number of instances. So did the LH seat stick.

You couldn't do that kind of useless rapid motion with the old irreversible hydraulic driven- cable controlled flight controls of yesteryear. The actuators generally had to move to follow up the input command. Until the cylinder followed up, you only had the limited motion.of the control valve travel available.

With a stick flailing around like that, you would have to mentally integrate your motion relative to the center detent to properly evaluate what the net effect of your control motions was. Are we sure that FBW is the better control system??:hmm:

[mm43]

The aircraft "knows" nothing. It relies on appropriate air data and "intelligent" pilot inputs to perform within its design boundaries.

AF447 did all it was designed to do, and when the "intelligent being" making the command inputs wanted NU, the aircraft complied.

What bothers me is the "intelligent" part of this equation was missing.

I doubt if any of the pilots on this thread would want the aircraft designers to put the "intelligent" part into the automation so that the aircraft "knows" best.

The degradation of control laws is indicated on ECAM as well as on PFD.

On ECAM
in ALTN : CAM EW/DFLT CTL ALTN LAW (PROT LOST)
MAX SPEED 305/.82

in DIRECT : CAM EW/DFLT CTL DIRECT LAW (PROT LOST)
MAX SPEED 305/.80
USE MAN PITCH TRIM

On PFD
The flight control status awareness of the crew is enhanced on the PFD.
Indeed the availability of PROTECTIONS is outlined by specific symbols = (green), and by the specific formatting of the low speed information on speed scale, in normal law.
When protections are lost, amber crosses X are displayed instead of the green protection symbols =.
When automatic pitch trim is no longer available, this is indicated as USE MAN PITCH TRIM amber message below the FMA.Auto trim is always available except when indicated to the contrary as detailed above.

As I have posited previously, the PF effectively spent 4 minutes battling with a compromised yaw damper that contributed to the roll and at no time was the SS left in the longitudinal neutral position. Without regurgitating the stuff long since posted (many times), if you simply don't know, the result will be equally simple.

[Clandestino]

See the point? That's about "graceful degradation" if I understand the concept correctly.

Quite so. Concept is giving as much protection as realistically possible. With all air data gone but with reliable inertial reference, everything goes out the window except the load protection.

BEA pretends Altn Law was the active Law all the way

BEA is Bureau d'Enquêtes et d'Analyses pour la sécurité de l'aviation civile. It is the French authority responsible for safety investigations into accidents or incidents in civil aviation. It doesn't pretend. It states so, accepting the full responsibility for its words. Where is the problem with that? You have good arguments it was otherwise? Let's see them!

P/P is always the Drill?

It is. It wasn't applied here. No evidence so far supports the hypothesis that A330 flight controls systems prevented the application.

if there was no "trimmed stabilizer" on a plane, the pilot did NO trimming at all

Nope. Even with fixed stab, elevator is trimmed for zero force, usually via tabs. I can't recall ever seeing aeroplane without pitch trim.

We have the STALL condition being announced loudly - and after so much analysis, very clear in its meaning to us - and throughout the duration of that announcement, we have an "automation" decision/action of employing the "autotrim" to max NU, which obviously if it did anything, it helped the STALL.

Trim was applied IAW control demand. Demand came mainly from right hand sidestick. "Stirring mayonnaise" and "it went forward a few times" are incomplete, therefore inaccurate and possibly misleading description of SS movement. SS traces are available in interim 3.

Now, can anyone provide FCOM reference for the triple adr fail caveat on abnormal law entry conditions.... I don't think it's in there.

It isn't explicitly written, however FCOM reference is consistent with BEA explanation - since all air data were rejected neither speed<60 kt nor AoA>30° triggering condition could be met.

What extra authority does abnormal law give over direct ?

None. It just retains G protection.

Green dot is not minimum clean speed. Green dot is L/D max. Considering this basic point, I fail to find it worth my time to further discuss this, or the AB with you.

Because you bring experience into the discussion, I've well more than three times the time you mention and have never NOT flown an aircraft that could simply kill me if I stalled them. But then again, I've intentionally stalled many a DC9 and am still here to tell the tale. Good day.


I am sorry you feel it this way but it really is not about contest between you and me. If it were so, I'd rather go down the PM path, in the unlikely event of finding debate worth pursuing further. As this is Profesional Pilots Rumour Network, open anonymous forum, I believe that details behind your temporary loss of control would be interesting to many a reader here. So what if your company allows regular operation below green dot while my does not? Is my wrong assumption that no Airbus operator would, reason enough to withdraw and retain all the information for yourself?

Nose refusing to go down when commanded so is definitively not normal behaviour of FBW Airbus, especially as with low speed you were far from high speed protection and I really doubt you hit G protection at -1. There must have been something else.

As for hours, they were not intended to illustrate my experience but that aeroplanes that are very likely to enter really unrecoverable stall are flying around in hundreds every day and no one makes a fuss about it. Every aeroplane equipped with stick-pusher is such. Now you mention DC-9, it's good example of T-tail without pusher (Super80's hydraulic elevator ram is not true pusher as it is not activated automatically) implying that T-tailed configuration is not automatically predestined to suffer from deep stall. BTW, there is no direct link between yoke and flight controls on DC9.

[TTex600]

Clandestino the DC9 series has cables directly connected to the control surfaces. IIRC, specifically the control tabs. The tab directly drives the ailerons and elevators. Transport category jets don't get any more direct controlled than the DirectCable9. Any other other point is purely semantics.

[HazelNuts39]

There must have been something else.Probably turbulence: Transition from updraft to downdraft could very well create sufficient reduction of "gee" to satisfy the "gee" demanded by a moderate nose-down SS input, without immediately dropping the nose.

[CONF iture]

Auto trim is always available except when indicated to the contrary as detailed above.
It should be the logical way, but Airbus thought otherwise as demonstrated in Perpignan.

I doubt if any of the pilots on this thread would want the aircraft designers to put the "intelligent" part into the automation so that the aircraft "knows" best.
I agree - Actually we would need less of that "intelligence" especially when some data are conflicting. After a discrepancy between AoA data + discrepancy between IAS we do not want automation to stay on the way - Autotrim is NOT welcome.

If I had to keep only one single item, I would say that autotrim has been the killer.

[BOAC]

Probably turbulence: Transition from updraft to downdraft could very well create sufficient reduction of "gee" to satisfy the "gee" demanded by a moderate nose-down SS input, without immediately dropping the nose. - the more we think we discover the worse it gets!

Pilot: I want the nose to go down

***: No! (Dave) I can achieve your demand for a change in vertical acceleration in another, far more clever way ( could even be nose up?)

Pilot: But I only wanted the nose to go down.:{

For heaven's sake - are you serious? Where have we gone wrong? (Answers on a postcard, please). When I move a control I expect a proportionate response in the desired direction.

[CONF iture]

IF789,
USE MAN PITCH TRIM is a message that appears in the PFD.
It appears as well in the ECAM as a reminder but at a later stage on the STATUS page once all ECAM actions have cleared.

For the Abnormal Attitude Laws I must admit I am not convinced by the BEA statement on page 40 :
The flight control law switched from normal to alternate at about 2 h 10 min 05. The alternate law adopted was alternate 2B and it did not change again subsequently. Due to the rejection of the three ADR by the flight control computers (PRIM), the abnormal attitudes law could only have been triggered for criteria relating to inertial parameters, but these conditions were never met.

AoA data were inertial parameters as described on the traces and they met the conditions ...

Also, as Machinbird reminded, what stopped the trim to reach the limit ?

[HazelNuts39]

BOAC,

Perhaps you should re-read TTex600's description of the incident in his posts #169 (p. 9) and #205 (p. 11).

[BOAC]

:confused: It was you I quoted!

[Zorin_75]

If I had to keep only one single item, I would say that autotrim has been the killer
Because they were trying to get the nose down for four minutes but autotrim didn't let them?

[idle bystander]

Sorry if this is going back a few pages. I'm still trying to catch up, but had to comment on this:

NARVAL wrote:

I think that we should keep in mind the very scant knowledge and training of the pilots at the time in the aerodynamics, stall recovery techniques, stall recognition…It was NEVER thought at the time that those planes could fly beyond the « approach to stall ». It was never thought either that the plane could « fly » with 40 degrees AOA and only 8 or 10 degrees of nose up.

And there was I, a very humble SLF, and happy to be abused with that name by all you god-like pilots, because I was under the impression that the reason I trusted my life to the people at the pointy-end was because they were like me, shared my fascination with things aeronautical, and had both the interest in and the knowledge of just what it is that keeps them up there amongst the clouds; that they actually understood something about the "little arrows" (underneath the wing) and the big ones (on top), and the significance of getting these the wrong way round.

And now I learn that it comes as a complete surprise to experienced 'pilots' that the flow of air over an aerofoil doesn't always produce LIFT, and that even though the nose is pointing up, you might be going down. Furthermore, I've learnt that the 'pilots' responsible for the safety of the SLF at the back of 447 hadn't actually been trained in what to do if the auntonomics dropped out and left them in control. Which makes me wonder why they were there. You could make more money by using the seats for more passengers.

Somebody please re-assure me that I'm wrong; that what NARVAL wrote, and what was so warmly applauded by quite a few 'pilots' on this forum, does not represent the average level of expertise of commercial pilots, that most of them do actually understand what keeps them in the air, because otherwise I'm sticking to sailing!

[Lyman]

It is a matter of some consequence...."Flight Law changed at approximately 2:10:05...." per BEA.

This is a word that invites doubt, and conjecture. It is an inappropriate statement, and not consistent with accepted levels of research. Alone, the phrase is amateurish, and there is no further refinement.

What prompted the statement? How was it derived? What is the Data referenced to prompt this speculation?

The only data I can find re: the LAW degradation is by the pilot, PNF.

"We have lost the speeds, ALTERNATE LAW."

Which ALTERNATE LAW? It remains unreported by the crew, or referenced by BEA per DFDR. The comment was made sixteen seconds later, after loss of A/P and A/THR.

Of some importance would be the record of airspeed loss, rate and value.

I continue to doubt ICE. A sudden loss of all three ADRs means simultaneous blockage. This is preposterous. A more probable problem would be turbulence, by way of windshear, or blanking of probes similar to a WS alert. OR AoA excursion WITH ROLL.

Clandestino: The fact remains, PF input a PITCH motive, and this defines PITCH, as in PITCH/POWER. It is most definitely possible his stick at two seconds after loss a/p was a preface to P/P. No?

idle bystander. You misunderstand. It is only remotely likely that these pilots were unqualified. By law, they were. This accident is not understood, and do NOT form conclusions as to safety from what you read here. There are perhaps a half dozen events that happened in the correct sequence that downed this a/c. Not that they happened at all, but that the sequence itself occurred. Incredibly remote. You may not believe, but knowing what I know now about 447, I would board with comfort this same flight, pursuant only to the fact that this crew also knew what happened.

The Devil has surprised us all. He saves up for generations to ennable such a catastrophe.

[Organfreak]

Lyman
It is a matter of some consequence...."Flight Law changed at approximately 2:10:05...." per BEA.

This is a word that invites doubt, and conjecture. It is an inappropriate statement, and not consistent with accepted levels of research. Alone, the phrase is amateurish, and there is no further refinement.

What prompted the statement? How was it derived? What is the Data referenced to prompt this speculation?


Though I am not inclined to blindly trust the reports that come from a French organization (because of France's huge investment in AI), I'm waiting for the final report before I'd judge that items are missing.

And, I don't understand your term, "inappropriate statement." Isn't that event documented be ACARS?

[Organfreak]

Lyman
It is only remotely likely that these pilots were unqualified. By law, they were.

Then the legal definition of 'qualified' was sorely lacking and needs revision, as has already been officially acknowledged. Agree that there are many questions and factors, though.

The Russian pilot who let his son 'steer' that A300 was 'qualified' too, and yet everybody died.

[HazelNuts39]

It is a matter of some consequence...."Flight Law changed at approximately 2:10:05...." per BEA.
(...)
What prompted the statement? How was it derived? What is the Data referenced to prompt this speculation?The DFDR includes two discrete parameters: Control normal law in pitch engaged/not engaged, and Altenate law engaged/not engaged (see page 107 of Interim #3). There is also an ACARS message to that effect.

Of some importance would be the record of airspeed loss, rate and value.Airspeeds 1 and 3 are recorded and shown in Interim #3.

A more probable problem would be (...) AoA excursion WITH ROLL.The FCPC's use the mean of AoA1 and AoA2 to eliminate effects of roll and sideslip.

[BOAC]

Mr Idle B - your plea appears to have gone un-noticed. Yes, there are many of us who understand the arrows and hooks and keeping 'rubber side down'. The problem we are facing here is that a particular system of flight (NB no names) appears to engender in some the chance to forget all this and become reliant on the system to look after them. I think you can be assured that many of these have gone away scratching their heads and may now be a little less relaxed about this and hopefully the manufacturers and training systems will also adjust. You will for example, note that the 'drill' taught for stall recovery has been changed following the accident and that I'm sure one large airline will be reviewing the abilities and training of its pilots. Looking at your location I would suggest you have a good chance of being behind someone 'wot knows'.

[CONF iture]

Because they were trying to get the nose down for four minutes but autotrim didn't let them?
No.
Because once trimmed the airplane was looking quite comfortable in a stalled status.
But before it started to autotrim :

It was definitely possible to hold the aircraft in the stall with 3 degrees of nose-up trim and full back stick, but it required effort
The aircraft wanted to nose down and recover itself
The nose wanted to come down naturally if I released pressure for even a split-second.

dixit DozyWannabe.

[GarageYears]

Quote:
Originally Posted by CONF iture http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/viewpost.gif (http://www.pprune.org/tech-log/468394-af-447-thread-no-7-a-16.html#post6811282)
Dani, what is that FCOM reference that could explain I was not able to get a forward autotrim ?

And yet on the A320 sim I did. Have you tried talking to the sim engineers about that one?As one who has spent my entire career working on, designing and programming simulators (admittedly my "bit" is the sound and comms bit, just so you get the full picture), any assumption regarding a specific edge-case operation should not be trusted on the sim until verified and checked against aircraft operation OR double-checked against aircraft data (assuming doing it on the plane is either dangerous or really difficult). I routinely find issues on certified and in-service-for-years simulators that were not caught or identified during routine operation and certification testing.

While the manufacturer of any simulator will aim for 100% accuracy, the available data is routinely found lacking, hence my cautionary note above. What may seem surprising to some is the fact that the data package supplied by the airframe manufacturer will vary from one customer to another - I recently worked two 737 platforms for different customers, and received different data from each, for the same system. Not entirely different, but 5% was. Eventually I was able to get the same consistent data, but I was lucky since I had access to two sources.

Aside from those parts of the sim using rehosted aircraft code (which has it's own issues), the device trusted for training is the result of hundreds of thousand of lines of code from a motley collection of software engineers, that typically do not follow anywhere near the same rigid procedures and practices employed when writing aircraft-bound code (costs alone would not permit). This is not to say they are not doing a great job, but trusting the sim blindly, in particular in areas extrapolated beyond the aircraft data or figured out by analysis of airframer supplied data, warrant second and third opinions before assuming the behavior is correct.

- GY :eek:

[Dani]

specific edge-case operation should not be trusted on the sim until verified and checked against aircraft operation

This is certainly true, but BEA has tested every steering input on AF447 against the real aircraft parameter and has come to the conclusion that they are completly consistent. There was nothing wrong with the way the aircraft behaved like this, it was the steering input that was wrong, i.e. they pulled too long and pushed too short. Simple as that. If they had pushed as long and as hard as they had pulled, the THS trim would have gone certainly back to a normal position.

You are hitting the wrong sack if you want to blame the autotrim. Autotrim is a perfect tool. They shouldn't have pulled into the stall.

[RetiredF4]

Dani
This is certainly true, but BEA has tested every steering input on AF447 against the real aircraft parameter and has come to the conclusion that they are completly consistent.

Where does this leave us?

BEA IR3 P41 The recalculated deflection angles for the elevators and the PHR are consistent with the parameters recorded Comparison.

BEA IR3 P42: Consequently, it would appear at this stage in the work that the bulk of the aircraft movements in the longitudinal axis (attitude, vertical speed, altitude) result from the actions of the PF, with the exception of small variations that are probably due to the meteorological disturbances.

BEA only tells us, that the flight control inputs in the simulator produced comparable outputs to the flight controls and caused comparable flight behaviour. Nothing more, and nothing less.

To read into those words that the aircraft is sanctioned and freed from having contributed in some way to the outcome looks a bit bold. A systemic inbuilt problem like unwanted behaviour of the THS autotrim (i´m not saying that it is one or isn´t one) would show in the aircraft as well as in the simulation. Only malfunctioning systems in comparison to non malfunctioning systems in the simulation would show as difference.

Where does it leave us then?
It only proves, that concerning the flight control system the aircraft had no malfunctions and that another A330 with the same crew (or with a different crew performing the same inputs) at the same place in the same environment would have ended in the drink too. This recognition might cause more headache for a manufacturer than finding the cause in one faulted part.

franzl

[Zorin_75]

No.
Because once trimmed the airplane was looking quite comfortable in a stalled status.
Maybe. But please don't disregard the THS arriving at the stops was preceded by almost a minute of ignoring a stall warning as well as what most would have considered basic airmanship...

BEA only tells us, that the flight control inputs in the simulator produced comparable outputs to the flight controls and caused comparable flight behaviour. Nothing more, and nothing less.
Dani and GY were discussing the fidelity of simulators. Nothing more, and nothing less. ;)

[OK465]

Where does it leave us then?

I think it leaves us with this, from page 77:

 throughout the flight, the movements of the elevators and the THS were consistent with the pilot’s inputs,

 up to the exit from the flight envelope, the airplane’s longitudinal movements were consistent with the position of the flight control surfaces,

(my bold above)

So that although the movements of the control surfaces were consistent with pilot inputs throughout the entire event, there is no direct statement of finding to the effect that after the aircraft exited the flight envelope the aircraft longitudinal movements were still consistent with these pilot inputs even though control surface positions were. Nor does this appear to imply anything further.

I would imagine this is still being investigated.

[Dani]

up to the exit from the flight envelope, the airplane’s longitudinal movements were consistent with the position of the flight control surfaces,

this sentence does not mean that they don't know the correctness of flight control surfaces movements, but: You simply cannot predict the flight path in a stall anymore, the aircraft is not behaving "aerodynamically correct" or "like designed". It rather moves in a random pattern, depending on chaotic aerodynamic laws, not predictable and not rationally explainable (unless many more factors would be taken into play, in a much bigger "resolution" of values and mathematical formulae).

[DozyWannabe]

Your A320 sim didn't trim up under STALL WRN, and yet my A330 sim did ... as also AF447.

On the contrary, it did trim up, but it hit a limit of 3 degrees nose up. So we re-ran the test by winding in full nose-up trim manually and even with full nose-up trim the sim pitched down successfully on elevator deflection alone before the trim started rolling forward (although the autotrim did respond very quickly - I made a point of adding it into my scan once we started recovery).

The Russian pilot who let his son 'steer' that A300 was 'qualified' too, and yet everybody died.

There's a little-known coda to that accident, and that is the story of how the pilots successfully recovered the aircraft from the initial stall, but overcorrected by pulling up too long and caused a second stall that sealed their fate. What the investigators discovered in the sim was that if the pilots had simply let go of the control columns, the A310's protections would have stabilised and righted the aircraft on their own. Sadly, the Russian pilots were not trained on this feature of the A310's design.

So that although the movements of the control surfaces were consistent with pilot inputs throughout the entire event, there is no direct statement of finding to the effect that after the aircraft exited the flight envelope the aircraft longitudinal movements were still consistent with these pilot inputs even though control surface positions were. Nor does this appear to imply anything further.

I suspect that this is simply an acknowledgement of the fact that they can't replicate the behaviour of the actual aircraft in the stall without stalling the aircraft and measuring it (any test pilots want to volunteer?). By it's very definition, stall is a regime that is out of controlled flight and there are myriad forces acting on the airframe that are not easily modelled.

[Machinbird]

You are hitting the wrong sack if you want to blame the autotrim. Autotrim is a perfect tool. They shouldn't have pulled into the stall.Dani, I would normally fully agree with your assessments, but the autotrim you know and love in Normal law is not the same autotrim in certain critical respects when in ALT2 law.

Ninety-nine point nine nine nine percent of your flight time or more has been in Normal Law. Just because your regular autotrim has been so sweet doesn't mean she does not have an ugly sister.:ooh:

[Lyman]

Zorin75

The THS did not travel to (-) stop. It stopped short, something less than a degree. Neither did it "start" after one minute of SW.

Take a look back at Takata's pic of the Recovered THS. Note the damage to the NU end of the screw. Impact? Possibly. But the damage suggests collapse of the thread collar opposite the implied direction of travel at water impact. Something like an airload, not a water contact.

[HazelNuts39]

BEA only tells us, that the flight control inputs in the simulator produced comparable outputs to the flight controls and caused comparable flight behaviour.
BEA tells us on p.41 of IR#3:
At the request of the BEA, Airbus conducted a simulation of the operation of the flight control computers, This could be a computer simulation rather than one in a fixed-base or moving-base flight simulator.
there is no direct statement of finding to the effect that after the aircraft exited the flight envelope the aircraft longitudinal movements were still consistent with these pilot inputs even though control surface positions were.
That statement presupposes knowledge of the aerodynamic characteristics outside of the envelope where these characteristics have been established by flight test, perhaps extrapolated using wind tunnel data. If these characteristics were known, it would not be particularly difficult to model them (at least for the longitudinal motion), and to use them in a simulation to produce your statement.

[Dani]

Ninety-nine point nine nine nine percent of your flight time or more has been in Normal Law. Just because your regular autotrim has been so sweet doesn't mean she does not have an ugly sister.

Maybe, I still don't see where autotrim was to blame in AF447's case. It did autotrim what the PF ordered. Autotrim has no artificial intelligence to know what's in a pilot's mind. It stupidly does what it has been told: When you pull for a long time it trims this position to zero force. That's the definition of trim. What's wrong about this function on AF447? If only he would have pushed the stick as long as he pulled it, autotrim would have ordered THS back, this I'm pretty sure.

[Lyman]

What is the purpose of "zero force"? Pilot feels nothing anyway, and the elevators can sustain and withstand the forces on their own. What the THS adds is lethargy when perhaps an abrupt input is necessary.

It's great for cruise. What is the need in ALTERNATE LAW?

Does the computer get sore muscles?

[GarageYears]

Zorin_75:
Dani and GY were discussing the fidelity of simulators. Nothing more, and nothing less. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/wink2.gif

Correct - my point really was that jumping in the next available A320 or A330 simulator and wringing the cr*p out of it into an upset condition (outside of flight data) puts you entirely at the mercy and competency of the individual simulator engineer responsible for that aspect of the simulator performance - so in the case of flight modeling you might happen upon a model built with sensible extrapolations and cleanly interpolated behavior, while other models may simply 'straight-line' the performance once the flight test data runs out. It is unlikely such a flight regime was tested beyond a joy ride or unintended upset from the less capable engineers testing the sim - the last thing on a persons mind at that point is the accuracy of the simulation. The same would be true of any other aspect of the modeling, be it hydraulic systems, electrical or whatever.

So, taking the trim behavior in a simulator, once into an upset condition, with possible invalid airspeed, etc, probably shouldn't be regarded as definitive. I'm one of those engineers and I wouldn't trust it. As noted before, the sound models I produce would NOT include a vertical speed component as a contribution to the aerodynamic noise 'hiss' model. I have not data to model it and would be guessing. I could probably make a pretty good guess and have something representative, but:
(a) I've never been asked for it
and
(b) I'll bet if I ask 3 pilots for a subjective assessment, I'll get at least 4 opinions....

I suspect the Airbus "simulator" referred to in the interim report was an engineering simulator based on flight modeling the aircraft behavior versus control inputs, not what we all know as a full flight sim - perhaps the final report will define this more specifically.

- GY

[RetiredF4]

Dani
When you pull for a long time it trims this position to zero force. That's the definition of trim.

no, it trims not for zero force, it trims to maintain or achieve an ordered load factor.

As we know, autotrim not works on behalf of the SS inputs, but on the order of the FCPC, which has an ordered load factor of 1 g (no SS input) or a change (decrease or increase ) of this loadfactor (SS input).

Example (and this is not far away from AF447):
When in ALT2 and the aircraft is in a climbing trajectory (make it shallow or steep, the difference is only time) and the speed decreases (no autothrottle), the FCPC´s will position first the elevators and then the THS in order to maintain 1 g in the climb to compensate for the decreasing speed, even when SS is in neutral / untouched position.

Without preotections in ALT2 THS trim might even drive NU with a SS-ND input, if the increase in descent rate (like in the stall of AF447) decreases the loadfactor more than a small SS ND command would demand and elevators are already full NU.

Therefore machinebird got it right:
Dani, I would normally fully agree with your assessments, but the autotrim you know and love in Normal law is not the same autotrim in certain critical respects when in ALT2 law.

franzl

[Mr Optimistic]

In terms of 'stops', isn't it usual to have software stops somewhat in advance of any mechanical stops. Is there really a discrepancy ?

[mm43]

Originally posted by Machinbird...

...the autotrim you know and love in Normal law is not the same autotrim in certain critical respects when in ALT2 law.Are you implying a suspicion that Auto Trim was misbehaving in ALT2, i.e. the systems functioned in a degraded manner as per the XL Airways / Air NZ A320 accident?
On approach to stall and taking into account the dynamic of the flight and of the complexity of the displays, the automatic changes in the control laws can fail to be perceived and their consequences can sometimes be misunderstood by pilots. In this case, the passage to direct law rendered the auto-trim function inoperative. Even if the amber USE MAN PITCH TRIM flag was displayed on the two PFD artificial horizons, the crew did not notice the position of the stabilizer and did not command the trim wheel manually during the twenty-five seconds in direct law between 15 h 45 min 15 s and 15 h 45 min 40 s. From this time on and for the rest off the flight, as a result of passing into abnormal attitudes law, the amber USE MAN PITCH TRIM flag was no longer displayed. The systems thus functioned in a degraded manner, without the real overall situation of the aeroplane being known by the crew.I feel that NOT calling and clearing the ECAM messages and following the UAS QRH procedures introduced so much fog into the situation, that a failure to notice the Trim Wheel turning sits equally in this patch of fog.

In short, the Human Factors were dominate in this accident.

[Dani]

RetiredF4:
no, it trims not for zero force, it trims to maintain or achieve an ordered load factor.


I don't agree. The whole AI's fbw system is made to maintain or achieve an ordered load factor. Not the trim sub system.

Remember: You give a sidestick input, that's the load factor you order. Now fbw computers calculate the necessary load factor. When you release your side stick (normal law), you maintain the ordered load factor.

What trim does is that it "neutralizes" long term load factor orders, so the flight control surfaces can go to neutral position.

[Organfreak]

Originally Posted by Organfreak
The Russian pilot who let his son 'steer' that A300 was 'qualified' too, and yet everybody died.
Dozy:
There's a little-known coda to that accident, and that is the story of how the pilots successfully recovered the aircraft from the initial stall, but overcorrected by pulling up too long and caused a second stall that sealed their fate. What the investigators discovered in the sim was that if the pilots had simply let go of the control columns, the A310's protections would have stabilised and righted the aircraft on their own. Sadly, the Russian pilots were not trained on this feature of the A310's design.

Oh, it was an A310? My mistake.
But I wouldn't call that detail "little-known." Hell, I saw it on Air Emergency on the idiot box just the other night! But, in their defense, they never knew what was wrong in the first place. I doubt they would have trusted (my speculation) the protections at that point. Did the A310 really have that feature?

[RetiredF4]

@Dani
What did i write?
I described exactly what you now say, but did otherwise in your statement. It does not trim for force, but for loadfactor.

In former non FBW systems it trims for force, trim eliminates the force on the yoke.

I hope, i didn´t run into my personal language barrier here.

franzl

[Organfreak]

Retired F4 done writ:
I hope, i didn´t run into my personal language barrier here.

Nope, I understood you perfectly the first time! :ok:

[OK465]

Once these characteristics are known, it would not be particularly difficult to model them (at least for the longitudinal motion), and to use them in a simulation to produce your statement.

HN39: Exactly. :ok: :)

We can only hope.

RetF4: The autotrim is not a pitch rate augmentation system, it is a follow-up. It does the same thing as any aircraft trim system and trims out dynamic pressure that would tend to alter the pilot's pitch command. Dynamic pressure has to change to result in an automatic trim change just as would occur in your F-4 (or mine) to clue you that you needed to input a pilot actuated trim change.

It does not trim for load factor, it trims for force (Q) which would alter the pilot commanded load factor or the existing flight condition load factor if the pilot was either not inputting a command (SS neutral) or unable to change the existing flight condition load factor with his command.

[AlphaZuluRomeo]

Maybe, I still don't see where autotrim was to blame in AF447's case. It did autotrim what the PF ordered. Autotrim has no artificial intelligence to know what's in a pilot's mind. It stupidly does what it has been told: When you pull for a long time it trims this position to zero force. That's the definition of trim. What's wrong about this function on AF447? If only he would have pushed the stick as long as he pulled it, autotrim would have ordered THS back, this I'm pretty sure.
Totally agree with you, Dani.
When I proposed that the (nose up) auto-trim should be inhibited if S/W in ON, it's not because I felt the auto-trim performed wrongly.
I see this feature (inhibition) as a supplementary "protection" against a worse upset. History teaches us that, sometimes, pilots do the wrong thing, specifically they pull when (nearly) stalled. No pilot in his right mind will do that, but still that happen.
On the other hand, I've never heard of a pilot "taking the time" to trim up (manually) his aircraft while "fighting" an upset, worsening it.

Then:
Provided the aircraft knows its current AoA (and knows it's too high), I think the aircraf should inhibit the NU autotrim.
With a 100% proficient crew, who reacts as soon as the S/W gets ON, this feature is of no use, I agree.
But with a less proficient crew, who for whatever reason delays his recovery actions (namely: nose down stick, idle power), the inhibition of the nose up auto-trim has 3 advantages IMO:
1] when, hopefully, the crew asseses that he's stalled and engage the correct recovery, the aircraft will be "less" stalled (lesser AoA) than it would have been with the "help" of a more NU THS. The recovery should then be quicker. That means higher, too. Perhaps, the difference in height will be enough to prevent the crash.
2] being "frozen", the THS won't (silencely) change the aerodynamics of the aircraft at a time when the crew may be trying to assess "what's going on". By not "discretely" changing a parameter (and subsequently the aircraft behavior), the inhibition of the THS may help the crew to asses just that.
3] in the event of a further command law reversion (i.e. alternate law to direct law, or alternate law to abnormal attitude law) which will totally disable the auto-trim, the crew will not have to think "hey, I did the wrong thing just earlier, and pulled my aircraft into a stall, let's push the stick and not forget to unwind the trim because auto-trim was available as I pulled, but is no more active now that I push because the aircraft switched to direct law".

All those reasons are tiny holes in the cheese, and of course are less important (IMO) than a crew performing the right action when confronted to a stall (warning). Nonetheless, clogging those tiny holes may perhaps save the day, one time. Then if there is no crucial disadvantage to do so, why not implement it? ;)

Cheers
AZR

PS: By the way, I just learned that USE MAN PITCH TRIM is not displayed in abnormal attitude law (in an A320 at last). That too is a "flaw" IMO.

[mm43]

The endless disputes regarding the niceties of G Load versus its application to Elevator and THS demand is getting rather tedious.

http://oi40.tinypic.com/slpdh1.jpg
Remember - same in NORMAL and ALTERNATE LAWS.

Nowhere have I seen a mention of anything different in ALT2, therefore why would the THS not supplement the G Load demanded by the Elevator to maintain the pitch effectiveness of the Elevator?

[gums]

Salute!

Decent explanation of the trim, OK.

OTOH, I don't think Retired thot the trim had anything to do with rates. And he can jump in here to clarify.

It is true that the trim acts to reduce the pilot input to maintain either an AoA ( older planes) or a gee ( at least two FBW systems I am familiar with). And the amount of elevator deflection or THS position will be adjusted accordingly. Am I good so far?

So am I off-base assuming that a constant gee command of, say 1.15 gee for a 30 deg bank turn with none of the "normal" laws in effect, would result in the THS gradually trimming to reduce the pilot's requirement to hold a bit of back stick?

Sounds fine to this old dinosaur.

But then I note that AoA protections ( I prefer "limits") are lost in ALT laws when there are problems with the ADR subsytems. So I can understand trimming by the system or manually by the pilot that could result in the jet exceeding the stall AoA.

I look at the Airbus protections and laws and am impressed by how many are related to attitude versus AoA or even gee. The pterodactyl FBW system I flew 15 years before the A320 was AoA dominant. At low AoA you could get to 9 gees, but as "q" decreased, you hit the AoA limit and the gee available reduced until it was one gee, So at 25 deg AoA we flew at one gee with stick all the way back, regardless of our trimmed gee. And I point out that we trimmed manually for gee using the collie hat or the trim wheel. So we could trim for zero gee and if we let go of the stick the jet would try to achieve zero gee ( neat feature to gain energy, called unloading). Our trim limits were about - 1.4 gee and + 3.4 gee. The Airbus doesn't work this way.

As far as the THS contributing to the prolonged stall? I would think it hurt, but was not the primary factor. As Doze discovered in the sim, the elevators had sufficient authority to get the nose down.

I strongly disagree with the loss of AoA "protections" when airspeed is FUBAR. If the initial pilots did not complain about the 60 knot value or even unreliable speed values, I understand. OTOH, I cannot understand why the "q" was not augmented by a simple WoW switch. After all, the jet is in "direct law" until liftoff, isn't it? And then switches to "normal" law. Or am I mis-reading the FCOM's and other manuals I now have courtesy of several here?

Lastly, and for those who have not flown to the limits and beyond... If the wing camber does not have a decent washout, then the wing stall will progress from outboard to inboard. This results in movement of the center of pressure forward and actually reduces dynamic stability more than static stability. Hence, it becomes harder to get the nose down. It also reduces aileron/spoiler effectiveness.

too much verbiage, and remember that I started as a dinosaur and then evolved into a bird, heh heh.

[CONF iture]

OK465,

My own understanding would tell me that RF4 is correct, but I could not prove you wrong either, maybe YOU are correct ?

How things are working in my opinion :

The input is full fwd stick in ALT LAW
The request is for a load factor below 1G
Both elevators try to honor that request with a down deflection
THS under autotrim command will try to neutralize that initial elev down deflection
As no change in the load factor takes place both elev quickly reach full deflection
THS keeps moving in a ND setting but at a slower rate still trying to neutralize elev deflection
Until effect eventually takes place


What I don't get in your view is that nothing can happen until trim is manually moved, and so in ALT LAW when autotrim is active and therefore USE MAN PITCH TRIM is NOT displayed. If you are correct and I did understand you well, there would be another serious question directed to Airbus.

[Machinbird]

Quote:Machinbird
Ninety-nine point nine nine nine percent of your flight time or more has been in Normal Law. Just because your regular autotrim has been so sweet doesn't mean she does not have an ugly sister.
Maybe, I still don't see where autotrim was to blame in AF447's case. It did autotrim what the PF ordered. Autotrim has no artificial intelligence to know what's in a pilot's mind. It stupidly does what it has been told: When you pull for a long time it trims this position to zero force. That's the definition of trim. What's wrong about this function on AF447? If only he would have pushed the stick as long as he pulled it, autotrim would have ordered THS back, this I'm pretty sure.
Hi Dani, the reason I called Alt2 autotrim an ugly sister is that it deceptively behaves exactly like in Normal law, but has no limits other than physical ones. Nothing more.

When a pilot is mentally confused about the practical meaning of Alternate law, as the PF of AF447 appears to have been, then it is more dangerous if the trim does not stop when commanded a particular direction until it reaches the physical limits.

Think about how often you have seen your trim approaching the physical limits in normal operation (assuming you feel the need to monitor it). Almost never, and definitely not in cruise no matter where your cg is.

I agree that the PF pulled the nose up into the stall using the elevator, and the THS only slightly helped the stall entry since it was perhaps about 1 degree (above cruise setting)during its run for the upper limits.

I have seen evidence in another accident report (DC-8) where the crew brought their roll control inputs to a higher priority than pitch control although they were testing the stall warning when they got into trouble and should have known that the source of their roll control problems was excessive AOA. When the shiny side starts to point down, you airline guys tend to give that a real high priority, don't you?:}

I believe that the PF for AF447 did do something similar. He over-controlled the roll and trusted Mother Airbus to handle the AOA while he sorted things out, forgetting that he was in a different Law where Mother Airbus had passed all responsibilities to him. He almost got away with it, except that when he finally began to get the roll and then pitch under control, the stall warning sounded and a fresh round of wing flailing began as the TOGA thrust (and excessive aft stick) sent the aircraft out of the envelope. The heavy buffet that must have resulted was another thing that must have increased crew disorientation.

PF's eventual adoption of full aft stick was an attempt to damp the bobbing of the nose of the now stalled aircraft (In my estimation.). By this point, he was in full panic mode because the controls were not responding properly. Logical thought was an impossibility.
The THS was quietly running nose up while the crew tried to make sense of this strange land and had the effect of trapping the aircraft in a deep stall. If it had not run nose up, it is not certain that a recovery would have been effected during one of the attempts by the crew of nose down stick, but by being trimmed so far nose up, it became a virtual barrier to recognition of how to escape the stall.

So autotrim only slightly helped putting the aircraft into a stall, but then effectively became a barrier to stall escape.
All those reasons are tiny holes in the cheese, and of course are less important (IMO) than a crew performing the right action when confronted to a stall (warning). Nonetheless, clogging those tiny holes may perhaps save the day, one time. Then if there is no crucial disadvantage to do so, why not implement it? http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/wink2.gif
AZR, looks like we are in agreement.:ok:

MM43, this should answer your question. Earlier speculation regarding possible disabling of pitch trim when all airspeed inputs are invalid is another additional possibility, but is not at all proven/demonstrated.

[Machinbird]

I mentioned an aspect of control input yesterday that I am not sure the majority of you picked up on. Once the aircraft is stalled, the control inputs do not have much influence on the aircraft, and sometimes act in a contrary fashion.

The elevators became fully biased 30 degrees nose up while the PF was attempting to control the nose bobble by holding full aft stick. Once the PF tried lowering the nose, he also continued to try to control the pitch (and roll) rates of the aircraft with the stick so the frequency of his control movements was much higher than the response frequency of the elevators. We have called this stirring mayonnaise and it is definitely a bad technique.

Now the A330 pitch and roll control system does not provide feedback to the cockpit flight controls (stick). If it was an older non-FBW aircraft, the stick would move in close relation to control surface position. The only way for a pilot to know the control surface position on the FBW Airbus would be to observe it on a cockpit readout (but PF wasn't looking there).

The aircraft's attitude indications on the PFD don't follow the stick any more.
Although PF is making significant nose down inputs, he is also making significant nose up inputs. To actually start moving the elevator from its full up position past neutral toward nose down requires sustained nose down inputs.

PF is thus clueless about the net effect of his total input on actual elevator position. We can see the average control inputs pretty easily on the DFDR readout, but the PF could not. The feedback channel he had used all his flying career was no longer available.:( He was operating open loop.

[gums]

Salute!

c'mon. 'bird.

Whatthehell are you talking about?

We haven't had "real" control surface feedback for 50 years.

And I don't understand all the rest of the last post.

[Old Carthusian]

Following the autotrim arguments - it all seems a bit tenuous to say the least. A trail of clotted cream perhaps?
Reading the interim reports again one can find no suggestion of this as a possible factor. I would submit that the only reason the stall was entered into and continued was the PFs actions. We have a known shock reaction for pilots - pull back on the stick and then a series of psychological effects which continue the action. Reread the third interim report (I admit it is harrowing reading) and it is clear that there was panic and a lack of understanding not a problem with the autotrim. Remember autotrim can be turned off by moving the trim wheel. There is no evidence that the pilot even touched it. Once again we are pushed back to training and lack of professionalism.

[Machinbird]

C'mon Gums. Didn't the stick move as you trimmed your F-101 from fast down to landing speed? :p Doesn't matter whether you are supplying the force to move the whole control surface, or just the force to move the input arm on a hydraulic control valve. That movement is feedback.

I have personal experience with the subject when a small electrical box hanging by its wire bundle began to block the pushrod leading to my stabilator control valve (mounted on the hydraulic ram). I could feel the contact when I flew slow (but not when fast). If that box had moved 1/4 inch further, I wouldn't have had enough nose up to put the flaps down and land back aboard ship.

The point is that on the A3330 as (Old Carthusian likes to remind us) your feedback path is visual from the PFD when hand flying the thing. But when the aircraft stalls, it basically stops following the stick, so you have no real idea of your control surface position without actually looking at the control position display. Does it make sense now?
Better yet, try looking at the control surface position (elevator) versus stick position plots at the end of the 3rd BEA report.

[gums]

Salute!

No problem, 'bird.

Until some of the dinosaurs here have flown the full FBW systems with all the limits and the coded limits by sfwe and firmwe and such, it's hard to explain.

Ya gotta "feel" it.

I was blessed by a system that didn't care about "autopilot" type limits such as attitude or roll angle. We had no limits on that. It was all gee and AoA and rate limits. Not "protections", but "limits". So we lived or died using the cards we were dealt. And the rules were simple. I don't see this with the Airbuss control logic. Sorry for all the folks here that fly the plane. But that's the way I see it.

I am disappointed by the lack of training concerning stall entry and recovery, mach buffet detection without the computers advising you, complicated control law reversion sequences, disregard of AoA when the speed sesors go south, and the beat goes on.

Make no mistake, all here, I do not absolve the 447 crew of major screwups. But I also feel that the basic design/implementation of the system should be very clear as to the absolute limits of the jet and not provide the crew with seemingly endless/annotated exceptions to the basic jet control laws they use for 99.9% of the time.

Sorry to become emotional, but I can sympathize with the crew to a point ( like a minute). Then I question their training and experience with critical flight dynamics.

To wit:

- flying with marginal delta between overspeed and stall at high altitude
- recognition of high mach buffet versus the effects of turbulence
- failure to realize that nose could be up, but the jet is stalled, and vertical velocity should provide an indication that something is awry

gotta go

[Machinbird]

Gums, when you compare what we learned about actual aircraft handling compared to what is presently being taught in the puppy mills, it is night and day. Our training had a price however. Not counting the cost in Jet fuel, and bent aircraft, some of our peers did not survive it,

The whole thing is a cost-benefits tradeoff, but it seems to this old coot that it has gone much too far and seriously needs to become more comprehensive and balanced.

A crew not recognizing a stall! That just should not happen. Particularly with the amount of time they had at their disposal to recover.

[rudderrudderrat]

Hi Machinbird,
Doesn't matter whether you are supplying the force to move the whole control surface, or just the force to move the input arm on a hydraulic control valve. That movement is feedback.
I agree.

The familiar feel of the control surface displacement with control yoke (or side stick) is completely absent on AI FBW. e.g. If you take off with a strong crosswind, the aircraft may roll rapidly shortly after lift off unless you make a roll input. That roll input could be tiny - but the control surface deflection would be large to satisfy the commanded roll direction. So if we have no idea how much the control surfaces are moving in response to the side stick inputs we are making, we have no way of knowing when we are getting close to control surface saturation (max deflection) - (unless we display the Flt/Ctrl systems page).

The crew probably never "felt" the stall - they only observed the effects of it then remained in denial and disbelief.

Q. How many Airbus crew have actually taken the simulator to the stall buffet in ALT LAW? (before AF 447).
How many of you have taken your conventional aircraft simulator beyond the stick shaker to the buffet?
Is the difference because it wasn't a requirement due to the low probability?

[AlphaZuluRomeo]

@ Machinbird (re: #369 (http://www.pprune.org/tech-log/468394-af-447-thread-no-7-a-19.html#post6813451))
Thanks :)
But I didn't write the first sentence in the quote you attribute to me ("So autotrim only slightly helped putting the aircraft into a stall, but then effectively became a barrier to stall escape.")
I'm not sure the autotrim was a barrier to stall escape (I understand "barrier" as something wich prevent you (strictly) to escape stall; THS NU will for sure delay the escape, but I'm not qualified enough to say it will prevent it, even if it stay full NU; in fact, my guess would be it prevents not)

[DozyWannabe]

Q. How many Airbus crew have actually taken the simulator to the stall buffet in ALT LAW? (before AF 447).
How many of you have taken your conventional aircraft simulator beyond the stick shaker to the buffet?
Is the difference because it wasn't a requirement due to the low probability?

Valid points made by yourself and Machinbird - *however*...

At the risk of sounding like a broken record, we have the Stony Creek 727 crash in which all three crew members mistook the shaker for Mach buffet and pulled their aircraft straight into the ground as a result, convinced the whole time that they were in overspeed - ditto the Birgenair 757 Captain. Then we have BEA548 in which a constant stick-shaker and two stick *pushes* were incorrectly diagnosed as false by the crew (who may have effectively been down to the two S/Os at the time). It's a comforting thing to think that if all aircraft behaved as they did in the past that standards would not be slipping and situations like this would be correctly diagnosed, but the stats simply do not bear this out.

mm43's extract from what looks to be an Airbus manual of some kind (I'd love to know which one) contains the legend "Don't fight with the stick; If you feel you overcontrol, release the stick.". It's pretty much accepted that the FBW Airbus setup requires a slightly different technique to get the best out of it compared with more conventional aircraft, but the methods to do so seem pretty well nailed-down, though I'm sure that it takes a leap of faith to release the stick under certain conditions.

For what it's worth I think that airlines should be re-evaluating their training - not just to include manual handling at altitude, but also basic aeronautical refreshers on recognising stall, dealing with stall recovery. If it means having to buy a bunch of Cessnas to do so then they should, after all they're the ones saving money with all this new technology, aren't they? :)

[Dani]

"Don't fight with the stick; If you feel you overcontrol, release the stick.". ...it takes a leap of faith to release the stick under certain conditions.


This is an extract from Airbus publication about Unusual attitudes, stall avoidance and unreliable speed, issued in light of AF447.

You can read it also in "A320 family instructor support" by Airbus training und flight operations support division.

There is another widespread misconception that "releasing the stick" means taking off the hand of one's side stick.

It means merely that you shouldn't apply force to it anymore. Leave your hand where it is, you have a nice support there, be calm, see what the aircraft does, check for another input. That's how you should do it.

[Lyman]

Someone who hasn't been on the KoolAde diet should develop Machinbird's post #370 further.

The PF input began immediately with a Roll Left and Nose UP. His mayonnaise stirring looks bad, but it is as Mach has said, he wasn't getting input/response sequencing.

Once the a/c balked at responding to PF's first attempt to correct (read the report), he parted ways with the a/c. He became a HUNTER (attitude), not a gatherer. Well and good to condemn, but without the connection hand to craft, the flight path became independent of the cockpit's control.

PNF? He talks a good game, but he isn't in the mix, and I have doubts his results would have been different.

So, after taking control, the PF begins to handle an a/c that is not responding well. He lost the plot almost immediately. The entire CVR is a rehash of every Bus quirk known to man.

What's it doing? The posturers and imposters here are a bit full of themselves. Opinion? I doubt two of three crews could have recovered that flight. The Bus is not a pilot friendly a/c in the stink.

Unstick? And leave the a/c to meander about the sky? What a crock. Damned if you do, dead if you don't. Not a pleasant place, of a Summer Night in the Tropics.

I suppose the Bus Fans have no choice but to condemn this crew. The alternative is to repeat, "What's it doing Now?"

[CONF iture]

As one who has spent my entire career working on, designing and programming simulators (admittedly my "bit" is the sound and comms bit, just so you get the full picture), any assumption regarding a specific edge-case operation should not be trusted on the sim until verified and checked against aircraft operation OR double-checked against aircraft data (assuming doing it on the plane is either dangerous or really difficult).
GY, thanks for that informed view.
What I can tell from my experiment is that the trim behaved as it did for AF447.
That was the main purpose of the experiment - I will try more when possible - Maybe he didn't trim down for another reason, we don't know, but he did not.

What I'm curious and nobody came with an answer yet, why the trim did stop short of the UP limit for AF447 ? (He did also in my experiment but a bit earlier around 12 deg)

That autotrim up under stall warning is an aberration.

Like Airbus and the concerned authorities not reacting as needed after the well documented Air Caraibes events is also an aberration. Place every 330/340 crew in a simulated exercice of UAS in CRZ configuration and we are suddenly so more 'clever' if needed.

[GarageYears]

Something to ponder?

The thread over the past few days seems to be fairly fixated on autotrim behavior and stick "feel" (or the lack of it, particularly w.r.t. trim). However I think (personal opinion, I'll take the flack) that in any control task, humans are amazingly adept at learning and understanding whatever set of controls we are given (subject to sufficient training/use/learning). What I see here is a collection of folk that have various backgrounds (F4, F16, Boeing this or that, and more) and I think it is fair to say each specific aircraft had unique "quirks". I see comments here related to the lack of trim response on the Airbus sidestick (unlike the yoke crew where trim unloads the force needed to maintain an attitude), but, 'hello!' the F-16 is no different... and in fact I'd state the F-16 is a good analog to the Airbus flight control system, except, more extremely, the F-16 sidestick moves almost not at all - I think the travel is something like an eighth of an inch (Gums?) total. Control is achieved not by waving the stick around but by applying pressure to it. Quite different. Similarly many of us will have played with various flight simulator games... while I suspect many here are gasping in horror at the mention of such 'toys' the point is even with significantly compromised controls (compared to the aircraft) many gamers become extremely adept at controlling the 'aircraft' and can fly the thing pretty much like the plane. What we do is we LEARN. Humans are good at this.

What's my point? The point is we can throw mud at the Airbus control system, but like or not, thousands of Airbus aircraft are trucking around the worlds airways with millions of passengers and they are not falling out the sky any more often that those from other manufacturers. The point is, the crews of those aircraft learn how they work and understand the behavior of trim, just the same way they learn the response rate to a stick input, and so on. Just because that control system is different to Boeing or Embraer or whatever, doesn't mean it is not as good. Clearly it is, since those planes are certified and make millions of flights daily.

You can argue as much as you like that changing this or that is the hail Mary for the aircraft type, but that just doesn't hold water. Does ANYONE seriously think Airbus is going to change the sidestick to provide force feedback for example? The stick currently is force 'loaded' (spring loaded I believe) and I don't really see the need to change that. But others have previously argued otherwise.

So, why'd AF447 fall out the sky, you might ask? Back to something I wrote earlier - "In any control task, humans are amazingly adept at learning and understanding whatever set of controls we are given (subject to sufficient training/use/learning)". This is what went wrong, not the aircraft design. For whatever reason (pitot icing), the automation dropped out, and as designed, handed the aircraft back to the most sophisticated computing devices on the aircraft - the humans. Unfortunately the most important safety device on the aircraft got it wrong. Unfortunately they got it wrong over and over. Zoom-climb (wrong), pulled into a stall (wrong), continued pull (wrong), TO/GA (wrong - but I'll pass on that since it seems this might have been a trained response), lack of CRM (wrong), and so on. Lot's of wrong here.

But what was really "wrong"? Training. Training. Training. With sufficient training the crews response clearly would/should have been different - very much so. Would it be different today - I suspect emphatically "yes". Because this accident has highlighted so many issues, any Airbus pilot worth his paycheck should have been following the accident investigation and learned a massive amount - mostly what not to do, but I'm sure a lot about the Airbus control systems. The key word in the previous sentence = LEARNED.

How did Gums learn to fly the F-16? Hands on the stick and throw the thing around the sky (some in simulators I hope... job security for me!), but NOT hundreds (or thousands) of hours tooling across the oceans on autopilot.... I see so many references to pilots with 11,000 hours (or whatever) and every time my immediate thought is "subtract ALL autopilot hours off that and what do you REALLY have???". Low hundreds perhaps, if we're lucky...

In my book this is the problem. The time when the crew were needed the most, was exactly when the automation took a timeout - and that corresponds exactly to the skill-set the crew has least ability.

So what am I advocating? More hand-flying on the line? Perhaps not - the autopilot is there for a good reason and does a great job. Simply holding the stick for hours transiting the Atlantic doesn't teach much. We need to get pilots into aerobatic aircraft and get their basic flying skills on the edge of the envelope up to snuff - recover from stalls, spins, etc. Then get those same crew into the training devices (simulators, flat-panel trainers, etc) and fail the automation and get their hands on the stick. Create situations where the control laws degrade. Learn Alt Law. A lot of sim time is spent training one engine out situations on takeoff, etc - are the current training scenarios really relevant today - how often do engines fail? I believe that LOC is the single most significant cause of accidents today - not engines failing/catching fire/etc.

Don't get me wrong - if there are simple changes to the systems within the Airbus cockpit that will help, they surely should be implemented (I suspect the stall warning inhibit below 60 knots should be revisited). But the single most significant change is reprogramming the HUMANS who get to sit in the very front seats.

- GY

[airtren]

You're right, but it's also a general statement of the need to be cautious about what is or is not "simple" in software without detailed knowledge. A fair few years in software development has taught me that it's very easy for someone to believe they know enough about the internals of a system to assess the impact of a change request, when in fact they don't.



Career experience may be different from person to person, particularly when it’s a few years worth. A certain amount of time is required for one to become a principal, and even more to be higher on the career ladder. Very Large, very complex software systems have been around for quite some time, and there are plenty of people with a few decades of experience of being major contributors in the middle of things, of being those that made things happen.

But this is besides the point. It does not matter how easy is to fix it. If it need be fixed, then it need be fixed. A signal from a manufacturer that is not confident it can fix a problem of minor magnitude, shows trouble.

And therein lies the dillema - warning vs actual conditions. Maybe I didn't expalin well.

You did explain well - it is fully appreciated - but there is also a misunderstanding, as I referred to the "state" or "condition" of "Stall of the airplane", as a generic term, not specific to the Airbus nomenclature that you’ve described.

Finally, the way I understand the THS, and it’s made clear by the few pages from when I should have posted this reply - sorry for the delay - I am not the only one. It seems it is a lot bigger problem to leave its behavior as it is now, than to fix it.

[BOAC]

Mbird - can you expand on Once the aircraft is stalled, the control inputs do not have much influence on the aircraft, and sometimes act in a contrary fashion. please? I am not sure I understand what you are saying and have a feeling I might not want to understand it either.

Gums - - flying with marginal delta between overspeed and stall at high altitude - you need to define marginal here, as where they were cruising on the carpet graph is where we all fly - day in day out, and is fine and safe..

[gums]

Salute!

Thanks for the nice words, Garage.

We had no simulator back in 1979. Didn't have one for another three years, and it was a POS.

We had a very simple FBW system with few "laws" or "protections" compared to the Airbus. Our "laws" were based upon maneuver limits and not "autopilot" functions like max bank angle, restricted pitch attitude, etc. Our "limits" were there to provide max performance while reducing the odds of a ham-fisted pilot getting into trouble.

Our autopilot was extremely limited in its authority. The GD flight control wizards didn't want something getting in the way of their system.

I see the reverse in the Airbus.

I do not want to see airline pilots "experimenting" with the limits of their jets, especially with 200 SLF's in the back. But I would hope that they would occasionally fly some planes that have classic stall characteristics and learn to cope with unusual conditions.

I had just arrived at Hill when we got the word that our neat jet, which could not stall or spin or....., could enter a "deep stall" due to the basic FBW design and the aft c.g. we used. So we saw the films and the test pilot interviews and we were PREPARED for when it happened to us!

We had little, if any, "feel" for mach buffet due to the wing design. So the Airbus crews had a leg up on us. But they also had a small envelope that allows for little error WRT mach and AoA. They had to be "better" than us in that regard.

My feeling is that better training will be the cure, and not a massive overhaul of the FBW system

[airtren]

I mentioned an aspect of control input yesterday that I am not sure the majority of you picked up on. Once the aircraft is stalled, the control inputs do not have much influence on the aircraft, and sometimes act in a contrary fashion. ....

PF is thus clueless about the net effect of his total input on actual elevator position. We can see the average control inputs pretty easily on the DFDR readout, but the PF could not. The feedback channel he had used all his flying career was no longer available.:( He was operating open loop.

I did pick up on..... At a quick reading, just didn't have time to confirm in a post. Am not sure how that counts in the flow of things, as those that need read them, and understand them are not those that are in agreement with you, like I learned unequivocally recently. Your contributions in the last several pages were masterful, but that bold last short sentence is a perfect engineering description, that I am most envy of. :D:D:D Thank you.
.

[CONF iture]

For whatever reason (pitot icing), the automation dropped out, and as designed, handed the aircraft back to the most sophisticated computing devices on the aircraft - the humans.
Automation did not drop enough : Leave the trim alone and we have a different game to play.
Then include it in the wrongs ... Why not ?

[airtren]

@ Machinbird (re: #369 (http://www.pprune.org/tech-log/468394-af-447-thread-no-7-a-19.html#post6813451))
...
I'm not sure the autotrim was a barrier to stall escape (I understand "barrier" as something wich prevent you (strictly) to escape stall; THS NU will for sure delay the escape, but I'm not qualified enough to say it will prevent it, even if it stay full NU; in fact, my guess would be it prevents not)

I think I grasp your delineation.

It may be just semantics, but "delaying", may practically mean "preventing it", when it's part of a complex set of causes of a final fatal outcome.

[AlphaZuluRomeo]

GarageYears,

Don't get me wrong - if there are simple changes to the systems within the Airbus cockpit that will help, they surely should be implemented (I suspect the stall warning inhibit below 60 knots should be revisited). But the single most significant change is reprogramming the HUMANS who get to sit in the very front seats.
I totally agree with your last post. As for myself, I concentrate on "small" technical problems (autotrim, stall warning) because I don't feel qualified to discuss -more important- training issues. Besides, here is the tech log.
The risk is of concentrating "only" on those relatively minor issues, and take them as an excuse to continue to "save costs" on the training...

[Lonewolf_50]

My feeling is that better training will be the cure, and not a massive overhaul of the FBW system
Yep.

It's been an expensive "lessons learned," hasn't it, this crash of AF 447?

It has cost dearly AF, 228 people and their families, and who knows how many others.

In its wake, it is likely that a good many AB flying folk (and organizations) have delved deeply into their machines and know them better now than they did on May 30, 2009.

To fly your aircraft you have to know your aircraft.

What was it we used to say in the Navy?

NATOPS is written in blood.

Looks like a few things have not changed yet ...

[Lyman]

From the git, AB has been marketing complexity as dependability, and "Ease of Operation" as simplicity.

Both are utter lies, and errant horse----. Training needs to start at the Line, and I don't mean the AIR Line. The Production LINE.

To require pampered pilots to inherit a wild thang in the worst of circumstances, without some history of mitigation/preparation, is manslaughter, imo.

My opinion, and we'll see what France thinks.

Wolf, I appreciate your experience, but flying the line is not Blue Water.
Nor should it be. These babies are not Ace Sixkiller, nor should they be.

They are Lambs for slaughter, 447 case in point.

[Machinbird]

I'm not sure the autotrim was a barrier to stall escape (I understand "barrier" as something wich prevent you (strictly) to escape stall; THS NU will for sure delay the escape, but I'm not qualified enough to say it will prevent it, even if it stay full NU; in fact, my guess would be it prevents not)
AZR, I apologize for including a sentence you did not author.:O It seems the wonders of the Windows operating system require great care to avoid posting stray cat and dog comments in conjunction with those you intend.
If I clarify my definition of a barrier as an impediment that can be overcome with some degree of difficulty, I think you will see that a we are still in agreement regarding the import of the nearly full nose up trim.


Does ANYONE seriously think Airbus is going to change the sidestick to provide force feedback for example? The stick currently is force 'loaded' (spring loaded I believe) and I don't really see the need to change that. But others have previously argued otherwise.
No, I don't think they are going to change that anytime soon. My point in posting the lack of feedback in the stick is merely to explain the "open loop" control condition the PF faced once the aircraft stalled. There was no convenient feedback path for him to know what kind of control displacement he had actually requested. This was primarily due to his extremely rapid mayonnaise stirring control inputs. If he had made and held a control input, then the surface would eventually catch up to his demand the way it did in the nose up direction. The rapidity of his control inputs well exceeded the ability of the control surfaces to respond.

Mbird - can you expand on (below) please? Quote:
Once the aircraft is stalled, the control inputs do not have much influence on the aircraft, and sometimes act in a contrary fashion.

BOAC, I am probably not telling you anything you don't already know. Once you stall you will likely find that your control inputs may have a reversed effect in the case of roll (due to adverse yaw), or that the surfaces are relatively ineffective and the aircraft's motions due to vortex shedding and cross channel aerodynamic coupling mask the effects of your control inputs. The elevator inputs are masked by the THS input and likely a post stall phugoid like effect results (a nose bobble). To have an influence, you need to make a control input and hold it or in the case of roll, you need to use the rudder and lay off the ailerons.
http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/reply_small.gif (http://www.pprune.org/newreply.php?do=newreply&p=6813834&noquote=1)

[Clandestino]

the PF effectively spent 4 minutes battling with a compromised yaw damper that contributed to the roll and at no time was the SS left in the longitudinal neutral position. Without regurgitating the stuff long since posted (many times), if you simply don't know, the result will be equally simple.


I might be wrong but that's not the way I see it. Yaw damper works as expected and only starts rudder-wagging when aeroplane is stalled and at low forward speed so chances are yaw damper was not compromised mechanically but rather by inefficiency of fuselage-blanketed rudder. Is there something I'm missing?

Probably turbulence: Transition from updraft to downdraft could very well create sufficient reduction of "gee" to satisfy the "gee" demanded by a moderate nose-down SS input, without immediately dropping the nose.

No can do. What you wrote is widespread and utterly wrong understanding of way Airbus FBW works in pitch in normal and alternate laws. Sidestick neutral iz not 1G it is 0G. Yes, you have read it correctly: sidestick neutral is zero gee. "You are pulling our legs!", you probably think. After all, whole lot of Airbus publications, FCOMs included, clearly state: "With the side stick at neutral, wings level, the system maintains 1g corrected for pitch attitude". It is so and it is true. So where is the catch?

Catch is that the sentence I've quoted is often understood to be the description of the principle on which Airbus FBW operates. It is not. It is the description of end result.

Sidestick command does not order G in absolute terms. It adds G demand to already measured, therefore if hit by updraft giving you 1.3G, pull on the stick that would give you 1.1 absolute from straight and level will now result in 1.4 pitch up. Push giving 0.9 would now be 1.2. Same goes for coordinated turn induced acceleration. In other words, stick G command is superimposed on measured level on normal acceleration. Why would anyone make so complicated flight controls system, Because...

When I move a control I expect a proportionate response in the desired direction.

...and that's exactly what you get with such setting. You might be commanding G instead of elevator movement but command sense is strictly conventional: stick down - nose down, stick up - nose up, lest gods of aerodynamics decide you have trespassed over AoAcrit and take away the lift from your wings, that is.

What our esteemed PPRuNe colleague has described as his own experience is what you would get if G command were absolute. In real life it is possible to achieve such a net result only with: severe malfunction of inertial reference, severe malfunction of flight control systems or severe turbulence. Until the time our honourable PPRuNe colleague decides to quit his incommunicado status and shed some more light on his story, I'll file it under "unreliable".

- the more we think we discover the worse it gets!
(...)
For heaven's sake - are you serious? Where have we gone wrong? (Answers on a postcard, please).

You, and I'm using "you" here in strictly plural sense, have gone wrong when you started believing very good sounding but flawed theories that resonated with your prejudices. Don't worry, it's basic human limitation.

I was under the impression that the reason I trusted my life to the people at the pointy-end was because they were like me, shared my fascination with things aeronautical, and had both the interest in and the knowledge of just what it is that keeps them up there amongst the clouds.
No. We were lured into spending shed-loads of money on CPL training, believing that once we graduate, large pay for short work hours and lot of time in downroute hotels with attractive, young, available and free-minded hosties await us. To this end we have learnt all JAA thinks we need to know about aerodynamics, which can be summed up as: BBDEA - AACED - DAADC - ADEBA. Alas, there was no pot of gold at the end of the rainbow so lucky few of us slave away on pay that leaves one on half ration, after paying off the installment of training loan. You know what is the worst about it? I am not being as sarcastic as you presume I am.

Somebody please re-assure me that I'm wrong; that what NARVAL wrote, and what was so warmly applauded by quite a few 'pilots' on this forum, does not represent the average level of expertise of commercial pilots, that most of them do actually understand what keeps them in the air, because otherwise I'm sticking to sailing!

Comfort can be always taken by scrolling the page all the way down and reading the big red script. Works like Prozac, if not better.

BEA only tells us, that the flight control inputs in the simulator produced comparable outputs to the flight controls and caused comparable flight behaviour. Nothing more, and nothing less.

(...)

Where does it leave us then?
It only proves, that concerning the flight control system the aircraft had no malfunctions and that another A330 with the same crew (or with a different crew performing the same inputs) at the same place in the same environment would have ended in the drink too. This recognition might cause more headache for a manufacturer than finding the cause in one faulted part.

You have summed it up brilliantly: any A330 with same malfunction and same control inputs would do the same. Therefore, no mechanical or electronic surprises were present. Why would that cause more headache for manufacturer, beats me.

So that although the movements of the control surfaces were consistent with pilot inputs throughout the entire event, there is no direct statement of finding to the effect that after the aircraft exited the flight envelope the aircraft longitudinal movements were still consistent with these pilot inputs even though control surface positions were. Nor does this appear to imply anything further.

AF447 was the first A330 that achieved such a high AoA - basically it went into uncharted territory. That's why sim BEA's sim assessments stops short of going into extreme AoAs. You might theorize and test scale models ind wind tunnel until the cows come home, there's no replacement for testing the real thing to know whether all the theory translates smoothly into practice. Why no test were done at 40° AoA with real aeroplane? Dangerous. Expensive. Unnecessary.

That statement presupposes knowledge of the aerodynamic characteristics outside of the envelope where these characteristics have been established by flight test, perhaps extrapolated using wind tunnel data. Once these characteristics are known, it would not be particularly difficult to model them (at least for the longitudinal motion), and to use them in a simulation to produce your statement.

I realize you were talking hypothetically. To set the record clear who might not understand: such a test will never be made.

On the other hand, I've never heard of a pilot "taking the time" to trim up (manually) his aircraft while "fighting" an upset, worsening it.

There's always first time: Tarom A310, near Orly on 24 SEP 1994 (http://www.bea.aero/docspa/1994/yr-a940924a/pdf/yr-a940924a.pdf)

I look at the Airbus protections and laws and am impressed by how many are related to attitude versus AoA or even gee. The pterodactyl FBW system I flew 15 years before the A320 was AoA dominant. At low AoA you could get to 9 gees, but as "q" decreased, you hit the AoA limit and the gee available reduced until it was one gee, So at 25 deg AoA we flew at one gee with stick all the way back, regardless of our trimmed gee. And I point out that we trimmed manually for gee using the collie hat or the trim wheel. So we could trim for zero gee and if we let go of the stick the jet would try to achieve zero gee ( neat feature to gain energy, called unloading). Our trim limits were about - 1.4 gee and + 3.4 gee. The Airbus doesn't work this way.

(...)

I was blessed by a system that didn't care about "autopilot" type limits such as attitude or roll angle. We had no limits on that. It was all gee and AoA and rate limits. Not "protections", but "limits". So we lived or died using the cards we were dealt. And the rules were simple. I don't see this with the Airbuss control logic. Sorry for all the folks here that fly the plane. But that's the way I see it.

I don't think I really need to repost pictures of A330 and Viper. One is passenger aeroplane, other is designed for combat. Every time my name came up on flight order involving A320, it was to move passenger & goods from A to B, if safely possible. Never was I ordered to strafe, bombard or intercept anything when strapped to A320 seat, which incidentally did not have rocket below seat pan or parachute packed in the headrest. Therefore, it is pretty safe to assume that design & certification criteria of two aforementioned superb machines (each in her own court) diverge wildly. Airbus logic is all about passenger transport. To repeat the lesson: stick free Airbus is flight path stable, not 1G chasing. As for G and AoA protections, principle is the same on F-16 and Airbus: full pull back in normal law will give you 2.5 G till AoA max is achieved.

Lastly, and for those who have not flown to the limits and beyond... If the wing camber does not have a decent washout, then the wing stall will progress from outboard to inboard. This results in movement of the center of pressure forward and actually reduces dynamic stability more than static stability. Hence, it becomes harder to get the nose down. It also reduces aileron/spoiler effectiveness.

Correct but pretty irrelevant to AF447. There was nose up moment from elevator. There was nose up moment from THS. There was nose up moment from underslung engines at high trust, yet the nose was mushing around 10°ANU. If the moment counteracting those wasn't pitch down of stalled wing, I really have no explanation what it could be.

I strongly disagree with the loss of AoA "protections" when airspeed is FUBAR.

Protections are lost because there is no simple way to compute whether airspeed or AoA is wrong. Stall warning remains, as the detection of aeroplane's energy state and associated decisions now is unloaded on intelligent entity, which must determine whether warning is true or false.

After all, the jet is in "direct law" until liftoff, isn't it? And then switches to "normal" law.
Correct.

The feedback channel he had used all his flying career was no longer available. He was operating open loop.

That would be very damning, if found true. Proper way to perform instrument flying in civil aeroplane is by visual reference to instruments, not to column/stick position. Taught from day one of IR training. That's why no one made a fuss about non-backdriven sticks on Airbus. At least no one not anonymous.

The crew probably never "felt" the stall - they only observed the effects of it then remained in denial and disbelief.
If they relied more on their hearing and sight, and less on their feelings, supposing they relied on anything at all, the outcome could have easily been different.

Is the difference because it wasn't a requirement due to the low probability?

Way around. It was not trained because of low probability but because it was believed that proper training in: aeroplane energy management, dealing with approach to stall and good aeroplane's stalling characteristic (for the cases where crew really needed time to gather their wits) would make occurence of extreme AoA stall in a passenger transport aeroplane so unlikely as to be unworthy of consideration. Both pilots of two man crew getting so confused to do almost everything wrong was beyond scope.

"Don't fight with the stick; If you feel you overcontrol, release the stick.". It's pretty much accepted that the FBW Airbus setup requires a slightly different technique to get the best out of it compared with more conventional aircraft, but the methods to do so seem pretty well nailed-down, though I'm sure that it takes a leap of faith to release the stick under certain conditions.

It does not. Stick forces notwithstanding, Airbus is pretty classic about airplane-pilot coupling. First time I've heard the phrase "stick-stirring", it was not related to Airbus but Let L-13 Blanik.


A crew not recognizing a stall! That just should not happen. Particularly with the amount of time they had at their disposal to recover.
But what was really "wrong"? Training. Training. Training

While I might agree, I'd advise caution not to slip into conjecture. First 3 reports are heavy on technical side while HF side is seemingly neglected, which comes as no surprise to me as it is much more difficult and time consuming part of the investigation. Human are not machines, which sometimes comes as mixed blessing. While aeroplane doesn't care what time of day it is, human beings tend to perform better at 10:00 AM than 04:00.

[Machinbird]

Quote:
Originally Posted by Machinbird
The feedback channel he had used all his flying career was no longer available. He was operating open loop.

That would be very damning, if found true. Proper way to perform instrument flying in civil aeroplane is by visual reference to instruments, not to column/stick position. Taught from day one of IR training. That's why no one made a fuss about non-backdriven sticks on Airbus. At least no one not anonymous.
Not really. This is really a Human Factors type evaluation of what the PF had to work with while using his mayonnaise stirring stick technique, and only applies while in a stall. He is not supposed to be in a stall, but it appears that mayonnaise stirring is a particularly bad control technique while in a stall. That might be a lesson we can take from this.

Protections are lost because there is no simple way to compute whether airspeed or AoA is wrong.
I'll bet there are quite a few engineers that do not agree.

Quote:
Originally Posted by Machinbird
A crew not recognizing a stall! That just should not happen. Particularly with the amount of time they had at their disposal to recover.

Quote:
Originally Posted by GarageYears
But what was really "wrong"? Training. Training. Training

While I might agree, I'd advise caution not to slip into conjecture. First 3 reports are heavy on technical side while HF side is seemingly neglected, which comes as no surprise to me as it is much more difficult and time consuming part of the investigation. Human are not machines, which sometimes comes as mixed blessing. While aeroplane doesn't care what time of day it is, human beings tend to perform better at 10:00 AM than 04:00.
Even the BEA seems to hold the viewpoint espoused by Garage Years and myself:
Consequently, the BEA recommends:
that EASA review the content of check and training programmes and make
mandatory, in particular, the setting up of specific and regular exercises dedicated
to manual aircraft handling of approach to stall and stall recovery, including at
high altitude.

I've been trying to pin down what specific training in my background convinces me that I would recognize the stall in the same situation that the AF447 crew faced.
The two factors are:


Having read D. P. Davies description of the deceptive nature of the stall in a relatively level attitude.
Having spent time maneuvering swept wing aircraft to their performance limits. (This has already saved my posterior on more than one occasion. Once was in a puddle jumper.)

[rudderrudderrat]

Hi Machinbird,
I've been trying to pin down what specific training in my background convinces me that I would recognize the stall in the same situation that the AF447 crew faced.
I was wondering the same thing myself. The Airbus Flight Training Study Guide (2003) had the following recommendation when in ALT LAW and approaching the stall: (see page 13) http://www.737ng.co.uk/a320training.pdf
"Eventually, the master warning and aural warnings will activate (crickets and “STALL, STALL” ). Recover at the stall warning by selecting TOGA thrust, maintain a pitch attitude for level flight and accelerate through VLS."

Unfortunately, AF 447 crew discovered that it doesn't work at FL 350.
(They probably had it demonstrated at 5,000 ft in their sim conversion course.)

[HazelNuts39]

Sidestick command does not order G in absolute terms. It adds G demand to already measured, therefore if hit by updraft giving you 1.3G, pull on the stick that would give you 1.1 absolute from straight and level will now result in 1.4 pitch up. Push giving 0.9 would now be 1.2.
Thank you for your elucidating explanation/correction. I'm amazed how one continues to learn new 'secrets' of the control system after so much time. What you write makes sense to me, but leaves me with a couple of questions:
I've read somewhere that full back side stick corresponds to a demand of 2.5 g. Suppose you are at 1.3 g with neutral side stick, then pull the stick to the back stop. What do you get?
Then we have this description in mm43's post #366: "With STICK FREE in turbulence, small deviations do occur on the flight path but with a tendancy of the A/C to regain a steady condion". Does that functionality only exist with stick free?
I realize you were talking hypothetically. To set the record clear who might not understand: such a test will never be made.Agreed. I've edited the last sentence of my post.

[Clandestino]

mayonnaise stirring stick techniqueThat technique, while patently wrong, would not be lethal if center of the stirring movements were set around neutral or moved forward as ADIs have shown pitch increasing. Problem is that average input was heavy nose-up. That's not ham-fistedness. That's confusion.

Recover at the stall warning by selecting TOGA thrust, maintain a pitch attitude for level flight and accelerate through VLS."

Unfortunately, AF 447 crew discovered that it doesn't work at FL 350.They even did not try to set attitude for level flight. How could they discover it wasn't working?

They probably had it demonstrated at 5,000 ft in their sim conversion course.Big part of being pilot is to be able to tell the difference between 5000 ft and FL330. Consequent to that is to know how aeroplane behaves at different altitudes or at least which altitude dependent procedure to apply.

I've read somewhere that full back side stick corresponds to a demand of 2.5 g. Suppose you are at 1.3 g with neutral side stick, then pull the stick to the back stop. What do you get?
G protection comes into play. 2.5 G slats retracted, 2G slats extended. As for how exactly G demand is related to stick position: me knows not. It felt linear and progressive in the area I have ever needed to use, which was certainly never above half travel, and that was good enough for me.

"With STICK FREE in turbulence, small deviations do occur on the flight path but with a tendency of the A/C to regain a steady condition". Does that functionality only exist with stick free? With stick in pitch neutral; yes. If you move it out of neutral you command flight path change so nose might be bobbing but overall it will move in the commanded direction.

Now you reminded me I have to further qualify my statement that Airbus is not particularly prone to aircraft-pilot coupling; it is valid in still air. In turbulence, tendency of the airplane to self-correct pitch and bank disturbances may (and too often does) lead to pilot induced oscillation. Statement you quoted is mighty correct and is followed by very good advice to avoid large interventions with stick.

[infrequentflyer789]

"Eventually, the master warning and aural warnings will activate (crickets and “STALL, STALL” ). Recover at the stall warning by selecting TOGA thrust, maintain a pitch attitude for level flight and accelerate through VLS."

Unfortunately, AF 447 crew discovered that it doesn't work at FL 350.
(They probably had it demonstrated at 5,000 ft in their sim conversion course.)

At what point did they try maintaining pitch attitude for level flight ? They (or at least PF) only tried pulling up. And they knew it. As someone said earlier on thread: PF responded, "But I have been climbing for some while...."

[infrequentflyer789]

Automation did not drop enough : Leave the trim alone and we have a different game to play.
Then include it in the wrongs ... Why not ?

First:

If this and other LOCs were down to pilots who could handle a conventional aircraft perfectly well in the same circumstances but were constrained/prevented/confused by the airbus flight control laws, then I'd agree - ditch Alt laws and drop straight to direct. Give the crew the conventional aircraft if/when things start going wrong.

...but I don't think the above is a correct assumption. There's a subset of pilots (probably including those who care enough to follow accident threads on here) who would handle direct law just fine (or better), but is that the majority when I also see comment after comment along the lines of Machinbird (http://www.pprune.org/members/306485-machinbird)'s "compare what we learned about actual aircraft handling compared to what is presently being taught in the puppy mills, it is night and day".

Second:

I don't think stopping autotrim would have affected this accident. I know you've argued that had the nose gone down they'd have diagnosed the stall, but I'm not so sure. When the a/c did pitch down in stall what was the reaction ? Pull-up, hard. If you're already prepared and briefed for stall in the sim, the nose drop is going to be obvious, but if you think the a/c isn't responding right (which looks like an issue in roll at least even before the stall) and you're pulling back and the a/c suddenly drops the nose, what will you do ?

Third:

Changing something one way to "fix" one accident may make things worse in other cases and end up killing more people. We should look at all the LOC incident history not just this one. I've done some looking, though not in any way a systematic survey, in what I've read the common factors were:

Airbus: no. FBW: no. Sidestick: no. Trim / AutoTrim: oh yes. Time after time. Not every incident, but probably a majority - and much more common factor than the others.

But what is the typical problem with trim, what's its MO when it kills ? Looks to me like it's trim-up before stall, autos drop out, trim not managed by crew then contributing to the upset and/or preventing the recovery. Exactly the opposite of 447 - which looks like the odd one out.

[chrisN]

IF789, in the sample of accidents you looked at, as well as finding a common factor with autotrim, do you see a common factor in what has been identified as the problem by more than one expert above – to quote, training, training, training - ?

Chris N

[infrequentflyer789]

Mr Idle B - your plea appears to have gone un-noticed.


Maybe not, but I can't provide the reassurance asked for. I raised similar concerns myself back here (http://www.pprune.org/tech-log/447730-af447-wreckage-found-153.html#post6648547) and triggered a well written response from PJ2 here (http://www.pprune.org/tech-log/447730-af447-wreckage-found-153.html#post6648687)


Yes, there are many of us who understand the arrows and hooks and keeping 'rubber side down'. The problem we are facing here is that a particular system of flight (NB no names) appears to engender in some the chance to forget all this and become reliant on the system to look after them.


Could be a lot of reasons for that. PJ2's comments referenced above; increased auto-everything; SPOs and regulation (RVSM) that all but prohibit hand flying; and Glass.

That last one's a huge difference for the non-pilot looking in (and maybe for the trainee starting out...). Look in at the old style hundreds of steam gauges and row after row of switches and be awed, and fearful - you better learn and understand every one of those, this is complicated. Look instead these days at three computer screens a handful of switches and (maybe) a joystick - well, how hard can it be ?

Yet the fundamentals of flight haven't changed, the machine underneath is as complex as ever, if not more so, and the margin for error doing a few hundred knots in an aluminium can at 30k ft is still just as small...

[Lyman]

Training is a Red Herring. With faulty probes, anomalous solutions, unquantified, and unbriefed, UAS is NOT a Training issue.

It is a BRIEFING ISSUE, and an Mx one.

Smoke, Mirrors.

[Machinbird]

That technique, while patently wrong, would not be lethal if center of the stirring movements were set around neutral or moved forward as ADIs have shown pitch increasing. Problem is that average input was heavy nose-up. That's not ham-fistedness. That's confusion.
Not disagreeing with you on the confusion.

I doubt that a person could make the control inputs that the PF did with just two fingers. He had to have palmed the stick. The forces appear to be too high otherwise.

Here is the thought experiment:

Suppose a pilot in a stall such as AF447 was in, places the stick full aft for a period of time and the THS runs up to its limit. If he now releases the stick and allows it to center, will the elevator center or remain at its last (30 degree nose up) position?

The answer is likely not as intuitive as it seems.
First, the aircraft is going to be in either g maintenance mode or pitch rate mode of C*. If airspeed is invalid, which mode is effective?

Next, doesn't the computer tradeoff elevator deflection for THS deflection. If the THS is at its limit, there is nothing to tradeoff in exchange for decreasing elevator deflection, is there?

Now overlay the aircraft's oscillatory pitch behavior in the stall over the top of this. What happens now?

[Machinbird]

Training is a Red Herring. With faulty probes, anomalous solutions, unquantified, and unbriefed, UAS is NOT a Training issue.
There goes a shoal of Red Herring right now:}.

[BOAC]

iff789 - your last two paragraphs are exceptionally pertinent.

"well, how hard can it be ?" - a few have discovered lately.

[HazelNuts39]

Sidestick command does not order G in absolute terms. It adds G demand to already measured,When the AP disconnected at 02:10:05, the A/C normal acceleration was 0.85 g (IR#3 p.42), zero V/S and FPA. If the pilot had done nothing, would the EFCS have maintained that level of 'g' (plus or minus variations due to turbulence)?

[CONF iture]

I don't think stopping autotrim would have affected this accident. I know you've argued that had the nose gone down they'd have diagnosed the stall, but I'm not so sure. When the a/c did pitch down in stall what was the reaction ? Pull-up, hard. If you're already prepared and briefed for stall in the sim, the nose drop is going to be obvious, but if you think the a/c isn't responding right (which looks like an issue in roll at least even before the stall) and you're pulling back and the a/c suddenly drops the nose, what will you do ?
To trim up in such circumstance must be a pilot's call, not one for the automation.
Let the crew make such a deadly mistake, don't do it for him please.

Trim / AutoTrim: oh yes.
Now we would need to evaluate both item separately ...

But what is the typical problem with trim, what's its MO when it kills ? Looks to me like it's trim-up before stall, autos drop out, trim not managed by crew then contributing to the upset and/or preventing the recovery. Exactly the opposite of 447 - which looks like the odd one out.
Because trimming to the limit of the AP like in AMS or LGW is not a better idea - AP should give back control before reaching such extreme because autotrim itself should not be allowed to go that far.

I note that limits for the 320 electric trim and manual trim are different.
It is apparently not the case for the 330 ?

[airtren]

Second:

I don't think stopping autotrim would have affected this accident. I know you've argued that had the nose gone down they'd have diagnosed the stall, but I'm not so sure.
I fail to remember reading a suggestion that "recognizing the stall" was a reason for the autrim to be detrimental. It was rather making the elevators NU even more effective, and the elevators ND less effective, and thus making overall a lot more difficult to get out of the stall.

Someone mentioned the stall incident, and recovery of the Tarom A310 approaching Orly, and pilot action on Manual Trim, and I've read that as a case, in which the pilot recognized early that the angle of the THS will affect how he can get out of the stall, and acted on it.


When the a/c did pitch down in stall what was the reaction ?
Pull-up, hard... That brings up another problem caused by the behavior of the machine.... They had the Stall Warning sound coming back each time, so under pressure and confusion, they went back to the controls input that silenced that.


Changing something one way to "fix" one accident may make things worse in other cases and end up killing more people. The cautionary attitude should not overwhelm the technical understanding of the problem.



I note that limits for the 320 electric trim and manual trim are different.
It is apparently not the case for the 330 ?

I am really curios to see the answer to this. I sense that someone, maybe a group, involved in deciding that, have been asked questions quite a bit by now.

Were the A320 limits on autotrim always that way? Did ever a change been introduced by an upgrade?

[Lyman]

Sly, Machinbird. It is not a training issue, per se, insofar as some here are extrapolating holes in ab initio for younger pilots.

STALL recovery needn't be trained in large jets: it is not supposed to occur, and no actual training can be designed for it anyway.

UAS cannot be trained, as in the type experienced lately in Airbus. Witness the meters from AB re: "Don't reconnect AUTOPILOT". "Review STALL procedures," etc. Then, "Wait xxx to reconnect autoflight," etc.

To a large extent, it cannot even be briefed: for 447, it was poorly addressed by both the a/c manufacturer and the line. The Probes issues, though patent, reflect the attitudes present that allowed this crash to happen.

It is NOT established that the PF's initial inputs were NOT an attempt to establish a flight path until speeds returned. How easy to discard this, since everyone wishes to discuss the follow on to this critical event's inception?

Crew were dumped into manual operation abruptly, the jet wanted handling, and it was downhill from there.

Red Herring? How about actively avoiding the discussion to be had re: the onset of Upset?

BEA will be asked to prove the airframe climbed abruptly and STALLED solely as a result of the crew's actions.

I see no such proof. On offer is a gassy spill from Herring merchants.

imo.

[mm43]

Machinbird in Post #403 (http://www.pprune.org/tech-log/468394-af-447-thread-no-7-a-21.html#post6815335)
Suppose a pilot in a stall such as AF447 was in, places the stick full aft for a period of time and the THS runs up to its limit. If he now releases the stick and allows it to center, will the elevator center or remain at its last (30 degree nose up) position?Interesting proposition. My initial response is to consider what the aircraft would do longitudinally if in DIRECT LAW.

We know that the CG is forward of the Aerodynamic Center or Neutral Point. That being the case, the Elevators must provide the following:-
(a) The AFT CG position is defined as - 1° of elevator deflection is required to pull a 1g Load Factor, and
(b) The FWD CG position is defined as - the maximum elevator deflection must provide at least the maximum acceptable load factor of 2.5g.

A problem exists in the AF447 stalled situation, i.e. a lack of TAS and faulty CAS, e.g. NCD.

But the aircraft is in ALTERNATE LAW, and the pitch characteristics are the same as NORMAL LAW which seeks a G response to commanded Elevator angle from the SS and as modified by the FCPC. Exactly how the FCPC preconditioning will react with dud air data is the big unknown, but with the aircraft stalled and falling at a nominal 1g, what is known from the DFDR traces is that a reduction of NU Elevator resulted in a reduction in pitch attitude, as would be expected with a CG well FWD of the Neutral Point. Not forgetting the pitching moment resulting from variations in thrust.

So your question - If he now releases the stick and allows it to center, will the elevator center or remain at its last (30 degree nose up) position?- seems irrelevant, though I suspect what you were asking is, "If the SS was left to center, what would the THS eventually do?"

Apologies if I have misinterpreted your post.;)

[DozyWannabe]

A problem exists in the AF447 stalled situation, i.e. a lack of TAS and faulty CAS, e.g. NCD.

At the start of the sequence, the speeds were only out from about 02:10:04 to 02:10:36 - just too long to prevent Alternate Law from latching - but interestingly, they come back well before the apex of the zoom climb is reached (The ISIS speeds come back just as the aircraft reaches the apex at about 02:11:15).

From that point the speed is reliable until the stall is so heavily established that stalled air begins to foul the pitot tubes, static ports and AoA vanes - which coincidentally is when the Stall Warning stops after sounding for almost a minute.

Exactly how the FCPC preconditioning will react with dud air data is the big unknown

The major THS movement happened while the FCPCs were getting good air data. The resolution of the graph is pretty lousy, but you can see the beginnings of THS movement following the elevators coming down when it was attempted both times - unfortunately neither attempt was held for long enough to make a difference.

So your question - - seems irrelevant, though I suspect what you were asking is, "If the SS was left to center, what would the THS eventually do?"

My educated guess (and it is a guess, so feel free to take or leave it as such) is that it would have gradually returned to neutral, following the elevator demand. Releasing the stick just after the apex may have been enough for the aircraft to recover itself (being docile in the stall according to the data we have), but within a minute, positive action was required to get them out of it. The nose drops below zero degrees *four times* after the air data goes out for the second (and final) time, but in every case it is hauled back up due to the pitch-up demands coming from the PF's sidestick.

[mm43]

Originally posted by DozyWannabe ...
My educated guess (and it is a guess, so feel free to take or leave it as such) is that it would have gradually returned to neutral, following the elevator demand.My thoughts are similar, though without receiving any positive pitch attitude command, would the THS return to say 4°NU. Remember, the A/P is OFF and the aircraft will follow SS inputs - which it was doing.

The Pitch Attitude / Flight Path Angle and/or V/S would "ring the bells" in this situation, but surely outside the software designer's criteria.

[mm43]

I have previously posted a link to the manual, but following recent requests here again is the link to the A330 Instructor Support Manual (http://www.scribd.com/doc/35605266/INSTRUCTOR-SUPPORT-Airbus-A330#page=1)

[OK465]

...following the elevator demand.

If the SS is neutral, the command is for 1 G. The aircraft was stabilized at 1 G in the stall. Why for gosh sakes would the THS have to move at all?

If it did, tending to create a load factor of less than 1 G, a situation Mach' alludes to, the elevator would have to then move NU to maintain the neutral, 'hands off' 1 G SS command.

THS may not necessarily follow SS input direction. Example:

In a dive recovery with the SS full back, load factor will be +2.5 G (1.5 over neutral) if the airspeed is 'adequate' to achieve +2.5 G (There will be, additionally, some MLA control surface action). If the aircraft continues to accelerate in the dive recovery, the THS (and possibly elevator) will bias in the ND direction, opposite the SS input, to prevent the G from exceeding 2.5 as the airspeed increases. This not a ND command, just a reduction in NU to prevent over-G but it is movement opposing the command input direction. Depends on airspeed.

Not that you would get there, but I would guess that if full forward stick were providing -1 G, and if the aircraft were accelerating, the THS would bias in a NU direction to prevent exceeding - 1 G (severe discomfort & nausea not withstanding). :yuk:

(Of course in Direct, instead of Alternate, you can get even more G...in trade for the potential detaching of parts of the aircraft.) :E

[HazelNuts39]

If the SS was left to center, what would the THS eventually do?After 02:12:30 the SS went through center a number of times, the elevator responded by coming down from -30 to -15 degrees, but the THS did not budge (see IR#3 p.41 for better resolution). FWIW, my educated guess would be that the THS would start to move when the elevator goes past the neutral position (as in Perpignan).

From that point the speed is reliable until the stall is so heavily established that stalled air begins to foul the pitot tubes, static ports and AoA vanes - which coincidentally is when the Stall Warning stops after sounding for almost a minute.
The pitots, static ports and AoA are all on the forward fuselage, not really in 'stalled air'. Some time ago I posted a comparison between the IAS recorded from the ADR's and the CAS calculated from ground speed. The two speeds started to diverge at around 02:11:30. For example at 02:11:43 the values were 100 kIAS vs 133 kCAS.

[mm43]

Originally posted by OK465 ...
Why for gosh sakes would the THS have to move at all?Right, no G demand equals no movement.

Originally posted by HazelNuts39 ...
... my educated guess would be that the THS would start to move when the elevator goes past the neutral position (as in Perpignan).Let's mark that answer as correct!:ok:

As I see it, while stalled at 1g, the elevator position is a demand for a increase/decrease in G which wont be met until the AoA is such that the wing is flying again. The THS will move to supplement the SS/Elevator demand as long as this G request is not being met. Elevator at 0 equals no G demand.

[gums]

Salute!

I go with Doze on this, plus last para of mm's post

As I see it, while stalled at 1g, the elevator position is a demand for a increase/decrease in G which wont be met until the AoA is such that the wing is flying again. The THS will move to supplement the SS/Elevator demand as long as this G request is not being met. Elevator at 0 equals no G demand.

Don't agree with last sentence, as a zero elevator position could result in negative or positive gee depending on airspeed and THS position, otherwise....

From what I read in the FCOM, the THS moves to reduce the requirement to hold back/forward stick. Just like non-FBW planes. So the continued back stick resulted in the THS trimming further and further. I can't find anything concerning THS movement related to measured gee, only stick position.

So I go with Doze that just letting go of the stick may have helped things at the apex of the zoom.

[Old Carthusian]

If I misinterpret Lyman I apologise but I rather think he is driving at one of two things. Firstly, a problem with the pitot tubes in which case UAS procedure pertains. Otherwise, failure to follow SOPs - as we know these were not observed. Either way we are left with a human factor issue. The difficult question, why were drills, SOPs and the like ignored? For everything else our shoal of red herrings is now following the trail of clotted cream (and that is a mixed metaphor!).

[infrequentflyer789]

To trim up in such circumstance must be a pilot's call, not one for the automation.
Let the crew make such a deadly mistake, don't do it for him please.

Now we would need to evaluate both item separately ...


We mostly agree. I think the autotrim discussion probably merits a thread in itself as it goes much wide than this accident.


Because trimming to the limit of the AP like in AMS or LGW is not a better idea - AP should give back control before reaching such extreme because autotrim itself should not be allowed to go that far.
Again agreed. In more general terms I fear the industry may have got itself into a nasty spiral:


more accidents per hour in manual flying therefore we should use more automatics
only times pilots get handed the plane is when George says "something's wrong because we've got to the edge of the envelope, I have limited (no) intelligence and don't know what to do now, so you have control. By the way, that's the stick shaker..."
resulting crash happens with human in control and is then another tick in the "mechanics are better than meat" box
return to (1)

I've thought for a while that it might even be beneficial if George took a mandatory random bathroom break every flight or so, just to ensure the real pilots are kept excrcised. Ecam: "you have control, I'm off down the back for a pee and to chat up the cute FA, back in 15".

Sadly even if it might be good idea over all, whoever implements it will have blood on their hands and a very unsympathetic hearing sooner or later...


I note that limits for the 320 electric trim and manual trim are different.
It is apparently not the case for the 330 ?I don't know. I'd really like to see more info on this 320 "limit", in particular where implemented and which laws and on what data, but I've found nothing other than the comments on here so far.

[OK465]

I'd really like to see more info on this 320 "limit", in particular where implemented and which laws and on what data, but I've found nothing other than the comments on here so far.

If the 330 SS were released at the apex of the zoom, all else equal, one of two things would have happened:

1. If the existing flight path at the time the SS is released would result in maintaining a speed/AOA in a range out of the stall (speed above, AOA below), then all is well and NO pilot intervention would be required to avoid a stall.

2. If the existing flight path at the time the SS is released would result in a continued decrease in airspeed and a subsequent continued increase in AOA to maintain the flight path, then NU elevator and follow up NU THS motion would occur ‘HANDS OFF’ until which time the pilot would have to intervene to avoid the stall.

This is why I’m a little suspicious of the A320 sim comparison, in which holding significant back stick force was described as a requirement, just to maintain 15 degrees of pitch PRIOR to the stall. Sounds like a low speed stability function of some sort was still in play in the 320?

In ALT2, the A330 would not require any back stick force (i.e. SS could be released to neutral) to hold the commanded pitch attitude/FP, and would do so as long as the aircraft maintained the speed/AOA to do so. Simulations can be ‘right on’ or not, and that’s why the regular evaluations are done using both automated QTG’s, and in the case of stalls (those which WERE done in flight test, i.e. evidently necessary, probably expensive, not terribly dangerous) manual QTG’s are flown to assure the nearest possible fidelity to flight test data that WAS made available.

Further, I would doubt that, once in the stall if the SS was released with the THS at 13 degrees, that the THS would of its own accord just roll back to a position of 3 or 4 degrees, trim positions that correspond to neutralizing the dynamic pressure for a speed range of around 265 KIAS down to around 215 KIAS at 1 G, not 150-180 KIAS and below in a clean config which won’t support a 1 G aero load factor.

If the SS had simply been released in the stall at 40+ AOA and 1 G, what 1 G unstalled flight path does anyone think would have eventually been achieved with the aircraft referenced acceleration already around 1 G and on a current flight path headed steeply down hill with dynamic pressure quite a bit less than that at 215 KIAS and above? ‘Splain it to me please. :)

[Lyman]

Without getting too excited, nor eliciting same from partisans, I believe the Pilots were not aware the airframe was STALLED.

Much of what we see in the BEA data supports this. There were insufficient cues to provoke a STALL RECOVERY, unless one certifies that TOGA and PULL qualify. Know the machine? Eh, Carthusian?

Erm, without question, and that means exactly, what? This flight?

This entire thread is peppered with assumptions of superior skills to this crew, which I find frankly repulsive, and quite literally, unsupported.

There is a soft bottom line, of course. To me, continued questions and a resistance to knee jerk pronouncements, plus an unwillingness to eliminate even a remote possibility, is preferred.

airtren, Without THS in the ascent, wouldn't the STALL have precipitated a Break that could have been recognised? Instead of a slide to mush that deprived some critical cueing? Not to mention a sluggish drop of the nose when commanded with FNU THS?

[Organfreak]

Lyman pontificated:
There is a soft bottom line, of course. To me, continued questions and a resistance to knee jerk pronouncements, plus an unwillingness to eliminate even a remote possibility, is preferred.


That's because only a fool would eliminate possibilities until the final report is issued.

Hope this helps.

:zzz:

[mm43]

While there is a lull in the current aerodynamic discussion, an Airbus initiative on future FDR options has been published in the August 2011 edition of FAST TECHNICAL MAGAZINE-#48 (http://www.airbus.com/fileadmin/media_gallery/files/brochures_publications/FAST_magazine/FAST48.pdf). In light of the difficulty in locating AF447, the options they are exploring for pre-crash alerting, jettisoned ELT and floatable QAR devices are touched on. Well worth a look.

NOTE: File is a large PDF - 9MB

[Lyman]

There are those here who reject other than PE as the procuring cause of this fatal wreck.

I believe the Pilots may have inherited an UPSET airframe, and were unable to recover the flight path, for reasons as yet undetermined. A chorus of 'consensus' notwithstanding, the Procuring cause has gotten virtually no attention, every thing has been a buzz of holier than thou judgment. Pontificate? As in: "These imbeciles?"

At the end, it is likely no complete certainty will be reached. There will be questions left, it is common.

A finer point for you? I think you may have misinterpreted my post. I have no inviolate opinion. ;)

[Organfreak]

@Lyman,
Sorry, I think I may have read it backwards or upside-down. :oh:

[AlphaZuluRomeo]

We mostly agree. I think the autotrim discussion probably merits a thread in itself as it goes much wide than this accident.
Why not :)

In more general terms I fear the industry may have got itself into a nasty spiral:


more accidents per hour in manual flying therefore we should use more automatics
only times pilots get handed the plane is when George says "something's wrong because we've got to the edge of the envelope, I have limited (no) intelligence and don't know what to do now, so you have control. By the way, that's the stick shaker..."
resulting crash happens with human in control and is then another tick in the "mechanics are better than meat" box
return to (1)

Nicely put!

I've thought for a while that it might even be beneficial if George took a mandatory random bathroom break every flight or so, just to ensure the real pilots are kept excrcised. Ecam: "you have control, I'm off down the back for a pee and to chat up the cute FA, back in 15".
Now that would be a reason to call automation "HAL". The under-tought is interesting :ok: but please don't try to sell it that way :p

[chrisN]

ATPL’s should comment rather than people like me, but I would have thought any manual practice in line flying is almost useless if just taking over from AP when in level cruise. I have noted several older pilots talking about taking every opportunity, SOPs etc. permitting, to do descents, climbs, and other things that are more active, to keep current; and deploring the modern tendency to keep hands off and let AP do it all.

In my line of (office) work, some of us used to query whether somebody claiming years of experience really only had about 1 year, repeated multiple times. I wonder about flying hours the same way (as somebody else here hinted at) – thousands of hours might be mostly thousands of times doing the same sort of hour, letting AP do it all, with actual decision making and manipulating controls being – what? A few hundred?

I would be interested in informed answers to that.

Chris N.

[TTex600]

ChrisN, this probably belongs in a thread of it's own, but hand flying a FBW "protected" Airbus in normal law, requires a different skill set than does hand flying a non "protected - normal law" aircraft. That in itself is not a bad thing. I have no problem switching between a simple Cherokee 180 and a FBW Airbus. The skill sets are different and it is quite simple to fly each with the appropriate skill set.

You wrote: ATPL’s should comment rather than people like me, but I would have thought any manual practice in line flying is almost useless if just taking over from AP when in level cruise. I have noted several older pilots talking about taking every opportunity, SOPs etc. permitting, to do descents, climbs, and other things that are more active, to keep current; and deploring the modern tendency to keep hands off and let AP do it all.

In my line of (office) work, some of us used to query whether somebody claiming years of experience really only had about 1 year, repeated multiple times. I wonder about flying hours the same way (as somebody else here hinted at) – thousands of hours might be mostly thousands of times doing the same sort of hour, letting AP do it all, with actual decision making and manipulating controls being – what? A few hundred?

I would be interested in informed answers to that.

I'm not certain what it is you are asking, but I'll attempt to answer the question I perceive you to ask.
The skill set required to hand fly a transport category swept wing turbojet at normal cruise altitudes with no abnormals and in fair meteorological conditions is FAR different than the skill set required to hand fly the same aircraft when said aircraft is turned over to the pilot in an abnormal situation in bad weather. (An additional bit of information you should know is that RVSM rules effectively outlaw hand flying at cruise.) Hand flying the above described aircraft at cruise in optimal conditions requires nothing more than a normal instrument scan and minor corrections. So yes, the skills required to hand fly in optimal conditions would not necessarily transfer to "recovering" the same aircraft when the A/P hands the pilots an unknown and abnormal situation. This is similar to the difference between a normal take off and one that includes a critical engine failure. If you take a proficient single engine pilot (centerline thrust) and put him/her in a light twin and include an engine failure on his first take off, with no previous demonstration or instruction in engine failure procedures, his performance is likely to be unsuccessful.

As mentioned, the skill set required to hand fly our aircraft in an abnormal would be FAR different than normal straight and level. The only solution would be to provide pilots with practice dealing with some of the potential abnormals.

The autopilot on my A320 disconnects at cruise with some regularity. Sometimes I do it myself when my Jeppesen manual bumps the disconnect button, sometimes it's the FO,..... Whatever the reason, the A/P disconnects, you take the controls and then re-select the A/P. Simple. I have never in my career, been handed an aircraft under the following conditions: at night, in turbulence, with questionable instrumentation, and in a questionable attitude. Neither can I think of any way in which to practice such a scenario.

[TTex600]

Earlier, Infrequentflyer789 mentioned it possibly being beneficial for the automation to "take a break" on occasion.

In my opinion, that would be of very little benefit, if any. As I wrote to ChrisN, the skills required to deal with an abnormal in cruise are far different than the skills required to take over from a lazy autopilot every once in a while. Allowing the automation to take a break would only provide practice in normals; what the AF447 pilots ( and most of the rest of us, including myself) really need is practice in ABnormals.

[gums]

Salute!

A very good question, Chris, and it gets to the heart of the matter WRT AF447.

Your observation hits home with this old military pilot who never flew a heavy. And I am sure that 'bird, Retired, Smilin', Wolf and others can chime in here.

Make no mistake, I used the AP a lot when not engaged in a serious mission requirement like air combat or dive bombing or flying formation or in-flight refueling or low level navigation at 200 feet or lower or.... I preached the value of even some crude AP's we had, like the one in the Viper. My other AP's in the Voodoo and SLUF were really good, especially the Voodoo. We could "couple" Otto to the ILS and simply observe and adjust the throttle until field visible. The F-106 could couple Otto to ground radar datalink and actually steer the interceptor to a position that enabled radar lock-on of the "enema" bomber.

The biggest use of Otto was in bad weather and having to plan an approach or calculate fuel required to an alternate or to simply get your act together. Then we had the long haul missions like flying across the ocean while sitting in a small chair with no snack bar or flight attendants, heh heh. Of course, we would have to snuggle up when weather was crappy, and then we had to get within 20 or 30 feet of a big guy to sip some gas.

Our good-natured jibes at the heavy pilots was that we had less hours but more landings. So in 4,000 hours I had maybe 3,000 landings. We also had 95% manual flying, often at the edge of the aero envelope.

So I feel we need to seriously look at the training regimen of the airline pilots. Get them into something capable of stalling and spinning and buffeting and....

Back in the 70's, USAF assigned T-37 trainers to the buff wings so the pilots could actually practice stalls and do some aerobatics. Was a well-accepted program, and was dirt cheap.

later,

[grity]

I was the painter of the stick movement between 2:10:07 and 2:10 18 at end of juli 2011

please, take a pin or a joystick in your hand and follow the movement, for every sec there is a number on the paint,

it is not so fast, the PF did not rest but he controled his moves, try it !
if you will make (shake?) mayonaise, like jcjeant called this picture, you have to move the stick 10 times faster


http://www.pprune.org/tech-log/447730-af447-wreckage-found-118.html#post6610311

http://i.imgur.com/X3HIW.png

[chrisN]

TT, and Gums, thanks. TT identified the first part of what I was asking about – sorry if I did not express it clearly enough, but you got there.

(I know amateur gliding is miles removed from flying airliners, but in instructing, once past the essentials, most of the further training is in dealing with the unusual, not seeing once again that the student can fly the easy bits with no problems. I would have thought almost all subsequent checks and training follow that, for power including airliner flying, in sims or reality; and to the extent possible, also in self-imposed currency practice in manual flying. It seems obviously most beneficial if handling the more difficult bits. You confirmed it.)

The other part I was interested in was the “000’s of hours of experience” vs “1 hour 000’s of times over”. (An exaggeration, but I think you know what I mean. Like Gums’s many landings. And I have even more landings per hour than him!) I am not criticising the AF447 PF; rather, if anything, questioning the selection, training and check regime that led him to being at the controls in a situation unprepared for. But just how many hours of his few thousand would have been experiencing new stuff ?

Any guesstimates from those in a position to say?

Chris N.

[chrisN]

Grity, I’m glad you posted that again – don’t know how to find the first posting easily.

I tried what you said. I think it serves to confirm something Retired F4 sent to me in a pm (he said I could refer to it here if I wished). He came up with a rationale for what PF was doing, and why.

While I understand F4’s detailed analysis, the amplitude of the SS movements (at M. 0.80-0.82) seemed to some other commentators, and to PNF if I understand his remarks correctly, to be inappropriately large or rapid. Again, ATPL’s and AB drivers particularly would comment better than I could. I know that my much slower glider, like most or all gliders, has an envelope that prohibits full control deflection at VNE or speeds approaching it. I would have thought that some limitation would apply equally to airliners – unless “Hal” protects regardless of what the SS calls for. (Sorry, but I get too easily lost in what still works in alt1, alt 2 and direct. I understand when people spell it out, but can’t remember in between times.)

Chris N

[Machinbird]

Nice Depiction of the stick movements Grity!:ok: Somehow I had missed this the first time.
Earlier I had noticed a ~2 second period between stick reversals in the BEA data. For a transport sized aircraft, this is very rapid. Mayonnaise stirring for sure when you consider the scale of what is happening with the aircraft. And look at the amplitudes of lateral stick travel!.
PF had to be all tensed up with his mitt firmly around the stick. Probably with his arm not properly supported as well. Hard to keep from pulling a stick back inadvertently under those conditions. (But keep in mind I've never sat in an Airbus Cockpit).

[DozyWannabe]

PF had to be all tensed up with his mitt firmly around the stick. Probably with his arm not properly supported as well. Hard to keep from pulling a stick back inadvertently under those conditions. (But keep in mind I've never sat in an Airbus Cockpit).

I don't think even with a death-grip on the stick it would be possible to inadvertently pull halfway back without intending to - there's a fair amount of travel involved. But the kicker is that he *slammed it back against the stop* from 2:11:40 to 2:12:15, and there is absolutely no way that could be done accidentally.

One of the things that has occurred to me recently is that with the arrival of big and powerful high-bypass engines 35 years ago, much was made of the "rocketship approach" to things like windshear - which over the years may have been corrupted into a belief that modern engines are powerful enough to get you out of almost anything. This fits with the PF's comments about being in TOGA, in that he may have believed that with the donks at full chat stall was an impossibility. I don't know what kind of groundschool knowledge was imparted to AF cadets, but if the fact that the higher you get, the less effective the engines are was not drilled in then it could have contributed to that kind of misconception. Obviously you have SOPs for things like engine-out in cruise in which descent to a lower flight level is necessary, but were the cadets ever taught why?

[TTex600]

(I know amateur gliding is miles removed from flying airliners, but in instructing, once past the essentials, most of the further training is in dealing with the unusual, not seeing once again that the student can fly the easy bits with no problems. I would have thought almost all subsequent checks and training follow that, for power including airliner flying, in sims or reality; and to the extent possible, also in self-imposed currency practice in manual flying. It seems obviously most beneficial if handling the more difficult bits. You confirmed it.)

You would think, wouldn't you? Sadly, in the US this is not exactly the case. The FAA requires recurrent checking. Not specifically recurrent training. My carrier, as do most others, are loath to provide more than the FAR's require because training is expensive. I take a PC (proficiency check) once a year and a PT (training) once a year, spaced six months apart. Sometimes I take two PC's a year due to pairing limitations in the training schedule.(my training partner may require a PC, a situation that makes us both fly a PC).

A PC is effectively an instrument checkride. In the Airbus, due to it being "stall proof", stalls are not checked. The PC consists of instrument departures, instrument approaches, engine failures on take off, and one or two minor abnormals (such as an airpac failure that leads to an emergency descent), one of the emergencies is usually a engine failure that leads to a fire that leads to an evacuation after landing. This sequence has not changed for me in over twenty years. Effectively, I re-take my ATP checkride over and over again. It's like the Bill Murray movie, Groundhog Day.

The PT I am scheduled for once a year usually consists of PC practice (engine failures at V1, for example) and instruction on a particular procedure (such as a specific arrival/approach/missed approach into a particularly dangerous airport. Guatemala City or Bogata, Columbia for example)

In summary, there is very little time to train things like high altitude stall recovery, and since it is not required, the airlines don't desire to spend the time(money) to do so. To my carriers credit, they did include the UAS/ADIRS failure procedure in our PT's last year. But we trained it once and I don't expect to see it again in the near future. This last PT, I spend a great deal of time taxi-ing around in significantly reduced visibility which is actually good training because runway incursions have killed more pax than Airbus UAS events.

The only answer I see to the problem would be regulatory. The international aviation industry regulators must demand that the carriers provide realistic training in a wider range of abnormal system and aeronautical events instead of focusing on things that were pertinent in 1966.

[jcjeant]

Hi,

DW
I don't know what kind of groundschool knowledge was imparted to AF cadets, but if the fact that the higher you get, the less effective the engines are was not drilled in then it could have contributed to that kind of misconception. Obviously you have SOPs for things like engine-out in cruise in which descent to a lower flight level is necessary, but were the cadets ever taught why? but were the cadets ever taught why?
Well if it's not taught in a flying school (different power effect with altitude) .. this will demonstrate that the schooling level in Françe is very low
It's just a physic principle you (normaly) learn in teenagers school level :)
I wonder if .. at end .. the famous "concierge" will be better choice for Air France than those cadets ...

[gums]

Salute!

You scaring the hell outta me, Tex.

How much of your checkride was engaging and disconnecting Otto?

Upsets?

Mach buffet versus basic turbulence versus approach to a stall?

The basic Airbus design seems robust, and we have all seen great examples of the airframe and pilot skill such as Sully demonstrated.

My point is that I am not worried about basic profiles and even emergencies such as loss of an engine or such. I am more worried about lack of basic airmanship when Otto quits and the crew has to coordinate, communicate and such.

I sure hope that all the airline pilots look at the AF447 example and demand better training for those 1 in 10,000 times when something goes wrong.

[Machinbird]

I don't think even with a death-grip on the stick it would be possible to inadvertently pull halfway back without intending to - there's a fair amount of travel involved. But the kicker is that he *slammed it back against the stop* from 2:11:40 to 2:12:15, and there is absolutely no way that could be done accidentally.
Dozy, In my opinion the reason for the stick against the stop after the stall had nothing to do with the earlier nose up inputs seen in Grity's graph. The post stall nose up was an effort to control the nose bobble in the stall. You can see clearly when PF changes his strategy in the BEA stick position charts.

The early nose up inputs have to be the result of an improper (palmed) stick grip. Do you see the NE-SW orientation of many of the motions? These indicate (at least to me) that PF was controlling the aircraft in roll with wrist flexion instead of rotation.
When he had to get to the far left corner on the chart, he was probably pulling his elbow off the rest also. Looks like the "Death Grip" on the stick was going full blast from the beginning. He wasn't at all relaxed.:uhoh::eek:

Maybe they should put force transducers inside the stick to measure the "squeeze" on the stick. That might tell the psychologists a lot about a pilot's mental state.

[TTex600]

Gums, I'm not in the training department, therefore I don't keep up with the specific FAR's. So this is from memory.

A standard FAR 121 Captains PC consists of: Low vis taxi, normal takeoff and area departure, airwork (stalls, steep turns, etc - the stalls are not required in the Airbus), one arrival, one normal precision approach, one single engine precision approach, one non precision approach, one missed approach, one CAT II/III approach (if CAT II/III approved) one V1 cut, and one emergency. The only times the A/P is required to be off are: one single engine ILS, and by at least MDA -50ft on the non-precision approaches. I'm probably missing something here, but for now I think you get the picture.

The only time we get training is in initial. After that, due to constraints of money, they give us the minimum, which consists of checking only. Occasionally we focus on something like the UAS/ADIRS, but that is the exception not the rule. I'm sure a training dept member will be able to give more data, but rest assured that we are given the little more than FAR mins. The same goes for recurrent ground school. It's now down to three days. One day on systems, one for GOM/FAR issues, and one for hazmat/security/etc. My current airline is my fourth and I must say that only one of the four actually provided me with thorough training in the airplane and on the ground. Interestingly enough, that carrier trained in the airplane (B1900) instead of using simulators.

It is my opinion that the US Airline companies rely more on the accumulated skill and experience of the Captains corps than they do on providing good training. IOW, they assume the Captains will give the FO's "on the job training" and that practice will continue from one generation to the next. This was likely good practice when the Captains were mostly military trained, but in the last 20 years the amount of ex mil pilots has dwindled. For the record, I am not military, but am well enough educated to recognize that the military produces/produced well trained pilots. I personally benefited greatly from flying with retired USN pilots early in my career. Unfortunately, historical accident statistics don't prove the past to be any better than the present. But I believe that to be an anomaly. Technology has improved safety, and has tempted airline management to hire less qualified pilots. When you mix a well qualified, well trained, well educated, well experienced pilot with technology in an abnormal situation you get the Miracle on the Hudson. Sadly, that generation of pilots is rapidly retiring.

Edit: One more thing, I am truly saddened and amazed by the number of pilots who chalk the AF447 accident up to nothing more than pilot error. I don't want to be seen as breaking my own elbow patting myself on the back, but I talk about this to everyone I can get to listen and most of them really can't conceive of it being anything other than a screwed up pilot. I personally believe the cause is much deeper than the pilot not knowing how to get out of a stall.

[Diagnostic]

In my opinion the reason for the stick against the stop after the stall had nothing to do with the earlier nose up inputs seen in Grity's graph. The post stall nose up was an effort to control the nose bobble in the stall. You can see clearly when PF changes his strategy in the BEA stick position charts.
Agreed completely, Machinbird. Like you, I see evidence (in both the control handling and CVR transcript) that the PF seems to have changed his mental picture (perhaps because he never found one that fitted with the plane's behaviour?).

IMHO the clearest example of incompatible actions for a single mental picture, are him mentioning TOGA (perhaps stall avoidance was in his mind then?), and at another time the "crazy speed" comment and (brief) deployment of the speedbrakes.

Therefore I believe comparing his actions at different times, to try to produce a consistent theory (or to try to disprove an explanation for one handling or another) is unfortunately futile, as his mental picture of the situation (and hence the reason for comments & control movements at each point) was likely varying throughout the event.

[DozyWannabe]

I can barely read a DFDR trace, and as such I'm certainly not going to attempt to second-guess the PF's thought process, but whatever it was, the overriding theme seems to have been to keep the nose up at all costs. The reason I mention the "rocketship approach" is because I wonder if he'd got it into his head that as long as he had the nose above the horizon and TOGA set, he was safe.

While the sim was being set up, I used the time to try out various different grip techniques on the sidestick. No matter how hard I gripped or whether I was moving with the elbow or wrist I could not get more than a fractional deviation in the pitch channel when moving it stop-to-stop in the bank channel without trying to add pitch input deliberately. This is not to say it didn't happen to the PF, but I don't think it's as easy as Machinbird thinks it is.

[Old Carthusian]

If we speculate on the PFs mental state (always a dangerous thing) I think we have to assume that he had only one thing in mind. All other information which might have contradicted this view was ignored or excluded. Sadly, the planes behaviour was not a factor in his actions. Evidence in similar situations tends to indicate fixation on one thing not a variety.
A study of cultural issues here would also yield dividends. Korean Airlines experience in the 80's and 90's is highly relevant with supposedly better trained military pilots messing up big time. It is also interesting to note the lack of CRM prevalent during that period. It is not where the pilot is from that is important but the culture and environment he/she operates in.
AS TTex600 notes past accident history does not indicate that things were necessarily better. But as accidents have gone down with better technology and more reliable aircraft, human factors have become more visible. Whilst a case can definitely be made that training is being neglected the airline culture has a more significant role.

[DozyWannabe]

I personally believe the cause is much deeper than the pilot not knowing how to get out of a stall.

Could you elaborate a little? I know you're talking about people you're actually meeting on the line here, but as far as this thread is concerned I don't think anyone has suggested that "Cause is pilot error, and we're done". Pilot error itself has myriad contributing factors including rest time, training, airline culture and human psychology.

As far as the airframe is concerned, it appears that recovery is relatively straightforward at the apex of the zoom climb, and becomes progressively more difficult as the aircraft sinks further into the stall. From the point they pass about 30,000ft on the way down it's impossible to know whether any airframe could have been recovered other than by using techniques which your average line pilot would not know, and in any case, from the moment they actually stalled they were in test pilot territory to start with.

[GarageYears]

As I posted previously and reenforced by TTex600 there seems to a problem with training and the overall approach. First as I noted and then again by TTex600, the simulator training syllabus for most carriers (all?) seems to have frozen in time, something like 25-30 years back - there is a lot of engine out/engine fire/engine fell-off type stuff, but little related to high altitude/UAS/near-upset. Does the current training regime match the real world as it stands now? My opinion is engines are very much more reliable than might have been experienced 30 years back, so are all these engine out situations worth the sim time? You tell me - I'm not a pilot, but I build sims, and model all kind of engine malfunctions, but nothing at all related to stall buffet cues... (at least in the sound department, may be the vibration boys do?).

Secondly, I know of several simulators that can be rapidly reconfigured to alternate aircraft - the cockpit representation is generic, but can be set-up as a twin jet, twin turboprop, light-prop, well in fact pretty much whatever. Further though, the flight modeling includes extended envelopes, up to and beyond stall - since some of the types modeled can be flown into and recovered from such an upset. So my question for the gallery is: "Would such a simulator be seen as an important adjunct to the existing FFS Level D devices?". You might say, "why bother? Put the pilot in a real plane and do the same thing." But I can very quickly see the finance department jumping up and down at the cost - the sim can run near 24/7 (ok, 20/7 with maintenance downtime), but doesn't eat fuel or cost much to run (versus any aircraft) and doesn't run the risk of falling out the sky.... The cost of that sim, well depends on a lot of details, but it should be on the right side of $5M, maybe quite a bit below that if smart choices are made.

A quick costs calc: ($5M/(10 years*365*20))=$68/hr purchase cost... (assumes sim lasts 10 years, runs 365 days/year/20 hours a day)

- GY

[TTex600]

Could you elaborate a little? I know you're talking about people you're actually meeting on the line here, but as far as this thread is concerned I don't think anyone has suggested that "Cause is pilot error, and we're done". Pilot error itself has myriad contributing factors including rest time, training, airline culture and human psychology.

As far as the airframe is concerned, it appears that recovery is relatively straightforward at the apex of the zoom climb, and becomes progressively more difficult as the aircraft sinks further into the stall. From the point they pass about 30,000ft on the way down it's impossible to know whether any airframe could have been recovered other than by using techniques which your average line pilot would not know, and in any case, from the moment they actually stalled they were in test pilot territory to start with.

You've already acknowledged the source of my statement. I was talking about the way some other pilots regard the cause of this accident. The lack of airline pilot participation in this very forum is a good indicator of the overall lack of interest I see in my fellow pilots. Most airline pilots I speak to about AF447 have only a passing familiarity with the details, they don't have the interest to go deeper than "the pilot stalled it and didn't know how to recover". I'm not a psychologist, so any conclusion I draw from their attitude is pure speculation, but I think that most Airbus drivers I talk to don't want to accept that the airplane is partly at fault because that would mean that it could happen to them. Very few human beings want to believe that some event could overwhelm them, I believe it is called "denial".

[DozyWannabe]

Well, they can't say the aircraft was entirely blameless because of the issue with the pitot tubes for starters, but are you saying you believe there's another issue at play?

I think you'll find a lot more pilot participation in the non-public areas of the forums, by the way.

[alcalde]

Hi there,
We as pilots are very interested in this forum despite all the comments.
I personally fly an A 330 last model and i feel confident with this bird.
I flew Boeing planes too and i believe is all the same job.
What we need is to fly more manually and train people to do it.
My Navy time told me that the checklists are written with the blood of others like this case
Best Regards
Alcalde

[Old Carthusian]

TTex600
Once again it comes down to human factors - know your machine and how to deal with issues. This was lacking. No aircraft is perfect and despite the current machines being far superior to previous machines they can still go wrong and have their foilbes. Pilots need to understand this and to be able to react correctly when it happens. Those that don't crash. You mention denial and this is certainly a factor but the very fact of denial is rooted in the mind of the denier. You are right that pilot error is far too 'glib' an explanation for the accident but it was a recoverable problem if the pilots had been able to react in the correct way.

[Machinbird]

Once again it comes down to human factors - know your machine and how to deal with issues. This was lacking. No aircraft is perfect and despite the current machines being far superior to previous machines they can still go wrong and have their foilbes. Pilots need to understand this and to be able to react correctly when it happens. Those that don't crash. You mention denial and this is certainly a factor but the very fact of denial is rooted in the mind of the denier. You are right that pilot error is far too 'glib' an explanation for the accident but it was a recoverable problem if the pilots had been able to react in the correct way.OC, Human Factors?

How well trained were the AF447 crew to handle UAS at altitude. Judging from the horrible example we have been puzzling over the last 2+ years, they were not adequately trained for the successive situations that they encountered. Whatever the emphasis of the training program, it did not prepare them for what they encountered.

I'd like you to think (way?) back to when you were learning to fly. Did you ever get in way over your head? Do you remember that feeling? Did the instructor steady things up for you and allow you to resume control? Were you lucky (if solo) and puzzle things out for yourself?

These guys got in way over their heads. There was no one there to punch the freeze button and explain what went wrong. To their credit, they kept on trying to the end. Unfortunately they did not understand that which is perfectly clear to us using our retrospectiscope.

The purpose of training is to keep us from getting in over our heads. As you fly, you will periodically find little things you didn't know or did not properly understand. Some of these are of minimal import. A few can be life threatening.

When training departments decide what to emphasize, there is a risk assessment of some type used to allocate training effort. Most accidents seem to occur in the takeoff and landing phase. Very few in the cruise phase. This accident unfortunately occurred in a less emphasized phase of flight. Furthermore, the system failure, UAS, had only recently begun to be visible in the safety radar scope, so training in that subject had to displace other training to be included in the time-limited training syllabus.

To sum up, the crew of AF447, particularly the two co-pilots were not ready for the UAS emergency that they encountered. They handled that emergency about as well as you would handle a night landing aboard an aircraft carrier.

[Old Carthusian]

Machinbird
I totally agree with what you say and I hate to think what a mess I would make of a night landing. However, training or lack of it is part of the human factor equation. As you mention getting in over one's head is part of learning to fly. But we should learn from that and emerge wiser and more aware. At first it seems so easy and then suddenly it isn't but after the experience we have more respect for the environment and the aircraft. I would hope that pilots flying the big jets would be aware of how to troubleshoot and deal with the issues they face. However, some are not and the whys and wherefores are what make up the human factors. Reading the accident report on Korean Airlines Flight 6316 is instructive. One crew dealt with the instrument problem successfully, the next crew did not and crashed the aircraft. Once again there were all sorts of human factors involved such as CRM (or lack of it) and lack of communication and training. Certainly training for UAS needs to be improved and it needs to be taught as a recogniseable issue. But the fact remains that there was a procedure availaible and a checklist to follow at the time. Maybe not clear but it did exist. It wasn't used and there seems to have been no attempt to troubleshoot the issue professionally. This is cultural as well as a gap in training.

[TTex600]

Old Carthusian, one can't "know his machine" when the machine is Dr. Jekyll or Mr. Hyde.

From what we presently think we know, the pilots dealt poorly with the UAS which lead to an upset. Once upset, they were faced with control harmony different than normal. How is the crew to "know the machine" when the machine isn't consistent?

[lomapaseo]

How is the crew to "know the machine" when the machine isn't consistent?

it's consistent in that it does what the pilot commands it to do. It's the pilot who is not consistent in knowing what commands to apply

[DozyWannabe]

If the airplane consistently does what it is commanded to do, how do you explain "auto trim"? When does the pilot command trim?

To offload pressure on the primary flight surfaces, exactly the same as autotrim does. Autotrim is a way of solving the problem of not having the surfaces transmit the pressure through the primary flight controls - nothing more, nothing less.

Why does it wander around the selected speed? (for you Boeing , Embraer, Canadair, Douglas drivers - the bus will vary by ten or more knots below 10Kft when fully automated. It trims for flight path, not for speed)

I'm sure that other airframes also "wander" to some degree, and always have, because even calm air is never 100% calm - it may not have been as apparent in the steam-gauge days due to the analogue nature of the instruments.

Contrary to the spin (partisan positioning) you read here, the Airbus takes what you input, processes your input through its brain and outputs whatever it decides appropriate.

That's one way of describing it - another equally valid way is "gives you exactly what you ask for in a manner that is appropriate to the conditions". In terms of flight path stability (which is after all, what the manual combination of thrust, PFC input and trim were trying to achieve in conventional jets) it is relatively unmatched.

Imagine, if you will, the steering wheel on your automobile randomly varying tire steering angle for a given steering wheel angle. Fun, huh?

Except that is not a fair description in that it isn't "random". The whole point of the "graceful degradation" aspect of the design was that it gives you as close to Normal Law handling as possible despite the fact that some of the systems required to give you that handling are not functioning correctly. A fairer analogy would be a power steering setup that has a partial failure mode making the wheel half as heavy as it would be with power sterring out completely.

[OK465]

How is it possible to quote someone on 22nd Nov 2011, 21:40 who doesn't post the quoted statements until 23rd Nov 2011 05:31??

Now that's spooky. :eek:

(HAL is at it again)

[Old Carthusian]

TTex600
I think that Jekyll and Hyde is a bit too much to describe an A330. I'm certain that it's not that bad. Iomapaseo sums the situation up excellently. Any airliner would have ended up in the same situation as AF447 if the pilots had performed the same actions. The accident wasn't platform related but crew related.

[DozyWannabe]

@chrisN - vBulletin uses server time as it's timestamp, otherwise threads would be unreadable. My guess is that the server was restarted at some point or there's been a database hiccup somewhere.

@Lyman - The sidestick is spring-centred, the PF does not have to "reindex it to neutral".

[chrisN]

DW, your post now numbered 457 has jumped in 2 above my 459, to which yours is a reply. You clearly did not send it at 09.32 UK time, so I wonder if your computer has defaulted to a non-UK time zone? The MS default is western USA – or something – might be worth you checking (it happened to me once).

Regards – Chris

[Neptunus Rex]

Without attitude display, PF was blissfully thinking he had only the ROLL to mitigate?

Lyman; perhaps I have missed someting, so please explain how the PF was without attitude display.

[Neptunus Rex]

My post in reply to #465 has goe into 459!!! So here goes again;

Quote:
Without attitude display, PF was blissfully thinking he had only the ROLL to mitigate?
Lyman; perhaps I have missed someting, so please explain how the PF was without attitude display.

[john_tullamarine]

Several posters have commented on the system's apparently putting posts out of order.

I can't claim to have much knowledge on how the system works in the background but my understanding is that posts are ordered by DTG.

Having said that we did have a period some time ago when the system went a tad strange and was logging incorrect DTG. Perhaps we are revisiting that situation again.

Either way, if you can tolerate the problem for the short term please and I'll refer it to the experts for attention.

Indeed, this post has been logged as having been made about 8 hours before it was made and posted in that incorrect DTG order - how quaint.

[TTex600]

Some of us have arrived at a conclusion, some of us have not.

That about sums it up.

"Dead men tell no tales"

I get the feeling that some of you would defend Jack the Ripper if he happened to use your favorite brand of butcher knife.

If the airplane consistently does what it is commanded to do, how do you explain "auto trim"? When does the pilot command trim?

Why does it wander around the selected speed? (for you Boeing , Embraer, Canadair, Douglas drivers - the bus will vary by ten or more knots below 10Kft when fully automated. It trims for flight path, not for speed)

For the open minded readers, I don't condem these actions as defective or bad; they just are what they are. Contrary to the spin (partisan positioning) you read here, the Airbus takes what you input, processes your input through its brain and outputs whatever it decides appropriate. The aircraft responds to the SS one way in normal law, and another in abnormal, and another in direct. Imagine, if you will, the steering wheel on your automobile randomly varying tire steering angle for a given steering wheel angle. Fun, huh?

[chrisN]

OK, I don’t know how for certain, but post 456 suddenly became 457. I think DW’s was inserted above. If not his, another was.

I suspect it is to do with our different computers (and maybe time zones) having different “real” times of posting, and the PPRuNe server sorts them into an order it recognises.

But what do I know?

Chris N.

[Old Carthusian]

Machinbird
Your post touches the issue of CRM as well as training very nicely. A proper division of responsibilities and teamwork come into play. These don't seem to have been present in this cockpit at all. The PF acted in a way that suggests he had no idea of what was happening and the PNF failed to take any action to correct this situation or to redefine the approach to the problem beyond saying "go down". At first the situation wasn't one where an intensive response was needed - sitting there, following the procedures would probably have solved it with AS returning after maybe a couple of minutes. Several threads back PJ2 suggested this very approach.

[Lyman]

From grity, PF input NURL at 2:10:08. The stick started at neutral. The a/c did not. It was NDRR. Did PF not re-index his stick to neutral? Did he carry on with NU 1/3 back as his neutral? It looks like it, the PITCH (stick) stays reasonably consistent whilst the roll was active.

Was he trying to maintain PITCH with a 1/3 back bias? That would explain the climb with no ND to arrest it. Did he climb, thinking he was 'maintaining'?

[jcjeant]

Hi,

DW
Quote:
Originally Posted by TTex600 http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/viewpost.gif (http://www.pprune.org/tech-log/468394-af-447-thread-no-7-a-23.html#post6823102)
If the airplane consistently does what it is commanded to do, how do you explain "auto trim"? When does the pilot command trim


To offload pressure on the primary flight surfaces, exactly the same as autotrim does. Autotrim is a way of solving the problem of not having the surfaces transmit the pressure through the primary flight controls - nothing more, nothing less."When does the pilot command trim ?"
You don't answer the question .. you just explain what is trim
With autotrim the pilot not command directly the trim
The position of the trim is a result of a combination of the elevators position and other factors
He have no power over the trim movements unless he switch to manual trim

[Machinbird]

But the fact remains that there was a procedure availaible and a checklist to follow at the time. Maybe not clear but it did exist. It wasn't used and there seems to have been no attempt to troubleshoot the issue professionally. This is cultural as well as a gap in training.
My one reservation regarding the above is that knowing procedures and having checklists is not sufficient to do the job in some situations, e.g. the "night carrier landing equivalent type situation" or other similar hands on intensive task. Only recent training buildup is sufficient to allow these tasks to be accomplished..

In this case, the crew probably knew their (current) UAS procedure, but they never got that far. They were likely hung up by the PF's problems in roll over-control.

For those currently flying the 'Bus, would you action the ECAM procedures while the PF is still having difficulty with the actual flying part of his duties?

[Lyman]

Establishing PITCH is an immediate concern, it cannot wait for ECAM, or conference with PNF.

TT. Do you get my question? Neither Pilot appeared to understand how in the weeds they actually were, from the very git. I believe the PF actually thought he had a reasonable NOSE, not one that was increasing its AoA. His lack of awareness not only seemed blase, it didn't get an instant "Hey!" from PM. Without attitude display, PF was blissfully thinking he had only the ROLL to mitigate? imo.

Again, at the outset, the a/c attitude was quite different from stick position.

Is this an awareness issue on the BUS?

[TTex600]

Machinbird, If one goes "by the book", the PF orders "ECAM Actions" or "Stop ECAM Actions" as necessary. In other words, the PF should be in command of the situation. I would not expect the PM to proceed with ECAM actions outside of my command. At the very least, the PM should query the PF for guidance before beginning ECAM actions.

In reality, I suspect that some PM's might begin the actions if they perceive the PF to be overloaded and they believe the ECAM actions beneficial to resolving the issue. If I believed the PF, in my case that would be the First Officer, to be in difficulty flying the airplane, I would take over. I believe that my First Officers would likely do the same if they believed I was having the same difficulties. They would likely wait slightly longer before taking over from the Captain, but they would take over.

[TTex600]

Lyman, I get what you are saying, No I don't think this is an issue in the Bus. At least not any more so than any other EFIS/"tape for speed and altitude" aircraft. The initial upset could have happened in any airplane that uses computer generated flight instruments. If I remember correctly ( I don't live and breath this accident and don't have the time to look back at the BEA rpts), the A/P gave up and gave the airplane back to the pilots while the aircraft was still stable. I have followed your thoughts and don't have any idea if you are correct. Hopefully we will learn all the facts when the final reports are issued.

[Lyman]

Dozy. You misunderstand. PF never allowed the Stick to visit its neutral point after taking control. It was aft the entire time of grity's pictorial. My assumption is that he 'established a neutral point', in his mind only, and hence disregarded the aft stick he consistently input.

See how the PITCH trace stays aft of neutral? PF may have been 1/3 of the way back at odds with the stick. (Actually at odds with the attitiude,:=).

NR. I can't imagine that he had an attitude display. How could he have, and keep asking for more NU?

[airtren]

My post in reply to #465 has goe into 459!!! So here goes again;

Please note that posts can be deleted, in which case, I believe the post count and posts numbers past the deleted one(s) get updated.

[john_tullamarine]

Post number is not critical and can alter but post order should be appropriate to DTG. Clearly something is not working quite right at the moment.

I've passed the information back up the totem pole so we can presume that the computer folk will have a looksee at the problem for us over the next few days.

(Following on from my previous post, this one is now logged with the correct DTG and is posted in the correct order - definitely quaint).

[OK465]

From the 'Las Vegas Slot Machine Technique & Aviation & Other Technology' weekly for today:

Time Travel research & testing at a well known Nevada military site have been temporarily suspended due to unanticipated effects on the world's most renown aviation forum, PPRuNe. Expect updates on the 10 o'clock news, if it actually comes on at 10 o'clock.

:)

[infrequentflyer789]

NR. I can't imagine that he had an attitude display. How could he have, and keep asking for more NU?

What did PNF have when he referred repeatedly to "go back down" and "According to the three you’re going up so go back down" ? From the phrasing (and maybe need to go back to the original French) would it be attitude, vs or something other ?

BEA state "Reading the three instruments (the two PFD’s and the ISIS), the PNF noticed that the airplane was climbing and asked the PF several times to descend." - how the heck they know which instruments PNF was reading I'm not sure, but maybe the assumption is that there was no other possible source to infer "climbing". If so, then logical conclusion is that no source for that information was unavailable...


And yet, like you, I've always wondered if attitude info was in some way lost. Post after post on here has said no way would you pull the nose over 10deg up in cruise, so it seems the only way to explain PF actions... but then not PNF comments. The HF report is going to be very interesting I think - there is much in that domain that just seems to make no sense.

[Lyman]

infrequent flyer 789.

The a/c was NOSE DOWN at handoff. It was also climbing at 1000fpm. So, yeah, VS. Robust UPDRAFT. I don't pretend to know what each pilot saw, but it seems that one was using ATT the other VS. At least at first. Then, perhaps each one, feeling 'burned' by one or the other of the instrument readings, switched horses.

Never the twain to meet. Frankly, in the longer term, the PNF had the better guess. It is clear from the absolute gitgo that the pilots were not flying the aircraft as most experts on this thread would have. But they were not up to the standard evident here, alas.

The ship was climbing 1000fpm. What does that say about the Zipper? With the turbulence ("fortes"), I still am not convinced ICE was the culprit re: speeds.

[jcjeant]

Hi,

The ship was climbing 1000fpm. What does that say about the Zipper? With the turbulence ("fortes"), I still am not convinced ICE was the culprit re: speeds. You can maybe never know .. as it's no alarm for pitot tube problems (like clogged by ice or other substance) on the A330
So it can be a real pitot tube problem or " turbulence ("fortes") "

[mm43]

I suspect the probable outcome will be described as "super-cooled" icing.

It appears from an article in news.com.au (http://www.news.com.au/breaking-news/supercooled-water-riddle-solved/story-e6frfku0-1226204294503) published a few hours ago that the lowest temperature that pure H2O will remain as a liquid has been extended from -41/-42°C to -48°C.

This would cover the AF447 situation where the nominal OAT was -43°C and an updraft containing super-cooled droplets could have created an "ice-block" on the pitots and possibly other surfaces within a second.

The initial pitch down and roll to right at A/P disconnect may have had as its origins, the same cause.

[infrequentflyer789]

The aircraft responds to the SS one way in normal law, and another in abnormal, and another in direct. Imagine, if you will, the steering wheel on your automobile randomly varying tire steering angle for a given steering wheel angle. Fun, huh?

[Car analogies - the staple diet of internet discussion boards, how did we manage so long without one ?]:E

Not so much random as predicatable change in feel. Not disimilar to power-steering failure... which happens. Most of us will never see it and never (these days) drive without power steering or remember what it was like.

However, in this case there was no change in control law in pitch axis - which was where it all went wrong - but a change in roll law may have pre-occupied the pilot and lead to failure to manage pitch. More like failing to steer the car right while worrying about accelerator or brake failure. Those do happen, and probably more often than steering fail. Many modern cars can go into a "limp home" mode for all sorts of failures (MAF sensor, DPF...) which is exactly the same principle as the degraded control laws. Fun ? Probably not, but not considered dangerous enough that drivers are given any training (or sometimes any information) in advance of it.

In the aircraft case, at least there is the sim to train and prepare for it. Except someone apparently decided it wasn't necessary to train the AF crew...


While we're on cars, it maybe worth comparing this case with the Prius accelerator issue. Initially blamed on the design/manufacture (type) and the computer control (fbw) going wrong. Turns out that in the end it's down to an age-old human-factors issue of not figuring out that something on the floor is stuck under the pedal. Yes, an element of bad design - floor-mat - but mostly HF issue that's happened before on other types. Just that the new computer control (and maybe the foreign mfr.) is a convenient initial scapegoat - one that some will still believe in even after all the investigation and reports are done and point a different way.

Also contributing is automation dependency - changes to reduce driver workload. Where a whole nation of drivers can't co-ordinate more than one foot, or take a hand off the wheel to change gear (because it's got a phone in it) - resulting in the removal of the mechanically connected clutch & pedal. Which, on those rare occaisions where your car decides to accelerate away uncommanded, is actually a really really important safety backup. [feel free to draw different conclusions on the a/c equivalent for that one].

[HazelNuts39]

Lyman,

Look on page 42 (IR#3, en). At 02:10:05 the vertical speed was zero, the next 5 seconds it was descending 400 fpm max, and at 02:10:10 the V/S became positive, i.e. it started to climb.

Moderators: This was posted around 19:00 GMT, in reply to Lyman's #483, posted 24 Nov 2011, 18:42 GMT.

[DozyWannabe]

Yi-yi-yi-yikes!!!
It certainly appears that the mayonnaise is well-blended.

The important thing to note is that in the videos the stick is quickly "blipped" in a given direction and allowed to return to neutral. What we see in the AF447 traces are inputs that are large, sustained and held for noticably longer.

[Machinbird]

Sure looked like a lot more than 900' remaining to me based on runway markings. They may need their RAS database checked.
Metric callouts?

[Lyman]

Lately when I try a post, it fails to post and I am automatically (?) logged out. Not that I have that much to offer, but it is strange.

I prefer to think of HF as judgment and abstract process, not floormat under pedal sender. Also CRM.

I take your point re: LAW degrade ROLL, while remaining consistent in PITCH. The serious problem as I see it is retaining both in the same stick.

Try teaching yourself to reconsider the control as sensitive in one plane, and in the other, not so much. Unlike others here, I don't think PF had ham hands, or a "death grip" on the stick; I think he was focused on keeping 447 off her back. In doing so, he slid through fore/aft movements, and..........

BEA stated that after the a/c was commanded up, it was not immediately responsive. That does not mean she didn't climb. Also, AoA was well ahead of PITCH, consistent with a strong updraft. We'll have to see why the a/c commanded 5000fpm down for thirty seconds prior.

[DozyWannabe]

The a/c was NOSE DOWN at handoff. It was also climbing at 1000fpm.

Again with the making stuff up. The nose pitched to a max of 1 degree down briefly for 3-5 seconds at 02:10:00 (still in autoflight). Disconnect happened at 02:10:05, at which point the pitch attitude was approximately zero. The climb starts at 02:10:15, because the PF has manually set the pitch attitude to about ten degrees.

The aircraft does not exceed 20 degrees of roll throughout the disconnect/zoom climb part of the sequence and only starts to approach 40 degrees of roll once the stall is well established. The protection limit of Airbus FBW is 67 degrees of roll. 40 degrees of bank is definitely out of the ordinary, but the notion that the PF was fighting to stop the aircraft from going on "her back" is nonsense.

[Lyman]

Cruise: +3. Add 1 degree, FOUR degrees nose low. And CLIMBING.

The airframe is not Protected in ROLL in AL2, so your "67 Degrees" is meaningless.

[grity]

Machinbird Nice Depiction of the stick movements Grity!http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/thumbs.gif For a transport sized aircraft, this is very rapid. Mayonnaise stirring for sure when you consider the scale of what is happening with the aircraft. And look at the amplitudes of lateral stick travel!.
PF had to be all tensed up with his mitt firmly around the stick. Probably with his arm not properly supported as well.in both of this videos is the speed of stick move maybe faster
(between 1:20 and 1:30.....)

LANDING EN LIMA - SIDESTICK VIEW (JUANDA) - YouTube

Landing A330-300 JFK VOR22L - YouTube

ok both are landings with slower speed, and low altitude, and the first one is not an A330 but to stir one`s coffee is obviously not unusual....???

@ lyman exist the (very smal) possibility of a undiscovered worn or brocken rod-spring into the sidestick ???

[DozyWannabe]

Cruise: +3. Add 1 degree, FOUR degrees nose low.

No - this is what we call "moving the goalposts" in the UK.

And CLIMBING.

No - even if you go by the vertical speed trace (which starts climbing before the altimeter trace), climb is not established until 02:10:11, at which point the pitch attitude is approximately seven degrees nose up and continuing in that direction.

The airframe is not Protected in ROLL in AL2, so your "67 Degrees" is meaningless.

You misunderstand me - I was not saying the aircraft was protected, I was saying that even with the aircraft at it's max bank angle in the stall, it was 27 degrees shallower than the absolute maximum the computers will allow when the protections *are* working, hence any idea that it was about to go inverted is complete hogwash.

I know you want to believe in a heroic PF that was wrestling a bad aircraft, but it simply is not borne out by the evidence. What we have is a relatively young pilot who was badly let down by his employer and was never trained for the situation in which he found himself. Having not been trained, he made the wrong choice when he raised the nose beyond five degrees. He compounded that by making another wrong choice and trying to keep the nose up and applied TOGA. He made a further wrong choice when he tried to deploy the speedbrakes. Bad move after bad move after bad move - but he'd never been told the right move.

@grity - exist the (very smal) possibility of a undiscovered worn or brocken rod-spring into the sidestick ???

Very unlikely, or the BEA's simulated responses would not have tracked so closely. The videos you post show normal sidestick deflection during low-altitude operations, including takeoff, initial climb, approach and landing - but you shouldn't see those kind of deflections in cruise.

[Organfreak]

@grity's videos:
Yi-yi-yi-yikes!!!
It certainly appears that the mayonnaise is well-blended.
(I do not want to fly in an elaborate video game!)
Thanks for these wonderful videos.

Something new occurred to me, although highly unlikely:
I wonder if the stick had a broken transducer. Perhaps that could explain all of these seemingly unexplainable inputs. Of, course, we hear no (as so far published) verbal feedback that would indicate such. Just another unsubstantiated thought to argue about. :rolleyes:

[Machinbird]

Grity,
The two videos are a bit of apples and oranges comparison with the AF447 initial PF control motions. Let me try to explain why:

First, the aircraft are landing, so the followng applies:

FLARE MODE
The flight mode changes to flare mode at landing, when passing 100 feet.
Flare mode is a direct stick-to-elevator relationship (with some damping provided by load
factor and pitch rate feedbacks). In addition, at 50 feet, a slight pitch down elevator order
is applied, so that the pilot has to move the stick rearwards to maintain a constant path,
so as to reproduce conventional aircraft aerodynamic characteristics.

Second, since the aircraft are landing, the aircraft must be in the proper location and attitude for "ground interface". This requires increasing attentiveness on the part of PF. It is a bit of a "crescendo" effect.




Third, There is a major difference in the control techniques displayed compared with the AF447 PF technique.

In the videos, the majority of the control inputs are pulses from neutral (Until Flare mode is activated).
On AF447, the control inputs were continuous.

[OK465]

Couple of things to note about the 330 vid at JFK:

1. At 33 secs point, after A/P disconnect, "Flight Directors, OFF".

Not dealing with SS moves, but I think fair game for a Tech Log comment:

2. RAS info on final: "Approaching 22 Left." Well and good.

RAS info on the runway after NW touchdown: "One thousand, two hundred remaining."... "Nine hundred remaining." Sure looked like a lot more than 900' remaining to me based on runway markings. They may need their RAS database checked. 22L is 8400' & the double high speed taxiway they passed on the right is only half way down. :confused:

(BTW Mach' stated the above post very well)

[OK465]

Mach', your post got shifted, but I think you're right about metric, it is a customer option. :)

The incompatibility with this on a US runway is that the callouts would not numerically coincide with the distance remaining markers.

And the RA callouts are in feet.....:confused:

(This random posting is like trying to talk to my wife.)

(And actually it's RAAS not RAS)

[john_tullamarine]

Board problems.

Re the comments about DTG and post ordering, as well as difficulty posting - I raised these with the hierarchy yesterday and the answer came back that we are experiencing the problems across all forums.

Both problems are ones we have had periodically in the past and it is a matter for the boffins to tweak a bit to fix things.

The delay on this occasion falls to the US holiday. Hopefully we will see the problems disappear shortly.

This random posting is like trying to talk to my wife

All of us married chaps have to let that one through to the keeper ...

[Organfreak]

@john_tullamarine
"...boffins.."

Isn't that some sort of a fish? :)

[john_tullamarine]

Guess I have to admit to being a boring old phart dinosaur of an engineer.

[Machinbird]

He made a further wrong choice when he tried to deploy the speedbrakes. Bad move after bad move after bad move - but he'd never been told the right move.
Dozy, please tell me what was bad about deploying speedbrakes?

The mistake was not leaving them out long enough to realize that they had no effect on the aircraft. If PNF had not climbed all over him immediately for selecting the speedbrakes, they might have had a chance to realize that the aircraft had something other than "Some Crazy Speed."

PNF was so uneasy by then, the "emotional sparks" in the cockpit must have been a foot long. This interpersonal tension interfered with everyone in the cockpit's ability to reason.

[HazelNuts39]

the BEA's simulated responses would not have tracked so closelyI would expect the PF to notice the different 'feel' of a stick with broken spring. The AB simulation is based on the recorded SS position, why would it be affected by 'feel'?

[gums]

Salute!

Looks like more efforts to blame the Bus versus the pilot, or a combo.

I have gone on record as feeling some Bus design features did not "help" the crew, but also feel most blame will still rest upon the shoulders of the crew and the mentality that the jet will "protect you".

Our physical feed back from motion/position of the stick is pretty decent if flying something as I did. Larger roll and pitch rates, and the inner ear sensors and the gee sensors in your butt helped. But the big heavies don't respond all that fast, so using visual cues ( like the instruments or outside the windshield) is the primary feedback, huh?

Spring failure is a red herring, IMHO.

About the only thing I would do is add force transducers to the grip as we had in the SLUF. That sucker had the same stick grip as the original Viper. So with "control augmentation" active, the first four pounds of stick pressure commanded control surface deflection with the angular position of the stick "frozen". Used to test this on test flights. Above the four pounds of pressure, you had to move the stick in an angular fashion, just like the "old" planes. If anything, the springs on the Bus stick may be too light. Maybe increase the pressure/force required to move that sucker a lot.

Just some thoughts from an old dino.

[HazelNuts39]

the nominal OAT was -43°C and an updraft containing super-cooled droplets could have created an "ice-block" on the pitots and possibly other surfaces within a second.Quite a jump from computer-simulated molecules. Clever molecules that avoided the ice detectors?

[TTex600]

Netstruggler, I am trying to explain to the non pilots on this forum just how difficult it would be to deal with varying control harmony.

When was the last time you flew an airbus at FL350 in roll direct? Does the roll response remain constant when roll rate degrades to roll direct?

A/P off. A/T off. F/D off. Thrust climb. What speed will it maintain?

[Machinbird]

They were stalled, that's what was bad about it! They were mushing at that point, and slowing down further might have rendered the aircraft completely unrecoverable.

Dozy, they didn't know that. Since the speedbrakes were rising from the wings into the wake of the stalled wing-there was minimal incremental drag. The effect was minimal with regard to incremental AOA.

If they had really been going at some crazy speed, they would have been thrown forward in their seats and had that impression confirmed.

As it was, they felt no more deceleration sensation than if the aircraft were on the ground, parked. That lack of sensation should have been a big clue, but the crew were so keyed up by then, they did not recognize the significance of the brief 3 second activation and its lack of deceleration.

It was not an error to deploy the speed brakes when PF did so.
The error was letting PNF cow him into retracting them prematurely.FCOM
SPEEDBRAKES
No Limitation

[jcjeant]

Hi,

Zorin_75
It didn't look much like a methodic attempt at troubleshooting though... These pilots have behaved like small children
Indeed .. in presence of a toy (to awaken the sens of curiosity) with levers and buttons of all colors a child will operate them out of curiosity
If its action on a lever will give a result (eg music) it will start its work on the same lever for a while
If there is no immediate result .. it will handle quicly one after the other without interruption the levers and buttons and will be frustrated
This is exactly what makes these pilots