LW. With respect, the discussion of instrumentaion comes up in the CVR, clearly, and neither one claims AFU. PNF, "lost speeds, ALTERNATE LAW".

"Je ne comprends rien". "I understand nothing". That is not, "my dash is AFU".

Then, "We've lost all indications." WE, not ME. It has NOT been discussed, to my knowledge. Neither pilot made the distinction to which you allude. It is for this reason I am concluding neither pilot requested hand off to the other. Later, this changes. I too am not sure what PF saw, and no one can be. The communication was restricted to adversarial critique, and lacked team work, I'll say that. But change controls?

CRM issues are critical here, but I am reluctant to grant them causative weight. I believe the a/c was UPSET, responding erratically (via instrumentation), and there is no reason to believe the PNF had a better shot. EXCEPT in retrospect.

There was a cadence in that cockpit that resists the panacea offered by those here who think they have the picture; they do not. I am at a loss to define one single cue/comment that was absolutely bankable re: recovery post A/P loss.

My jumping into an ongoing discussion with you or with other posters is to comment on incorrect and misleading statements in an area i feel familiar and competent with.
As you recognize yourself that may happen with you more often when you are making statements outside your primary area of knowledge and expierience.

franzl

On the line or when training? During training then of course the situation is different (and as an aside I'd never consider independent sidesticks to be a good idea in a PPL trainer), however on the line with SLF behind you, isn't it better to be absolutely sure (even if to be sure takes only a fraction of a second)? I can't help but think that if it were me and I'd just taken control, misread the situation and caused a crash I'd be absolutely gutted.

So would you feel better, if you are being crashed because taking too long to come to a decision?

Pilots sit in the front end to make those decisions and act upon them. They are paid to be prepared and act.

franzl

Dozy--
OK, don't call it an "algorithm bug," call it a "specification," who really cares(?), BUT, otherwise, it appears that everyone who has weighed-in on this shortcoming appears to agree! How 'bout THAT??? In speculation mode, it is possible that the designers/programmers never foresaw this scenario. Ya can't think of everything, after all (until it happens).

There's no doubt in my "mind,", albeit no proof, that the on-and-off behavior of the SW did not help the pilot's understanding of the sitch.

Now.
I'd be the last one to genuflect, although I have tremendous respect for ATPLs in general. OK, say you're right: it's the same old culprits (I wouldn't know). Consider this: again, I have no flying experience and no axe to grind, but I came blowing in here out of the blue, and immediately and independently saw the sense of the yokes argument. Again, no proof, but what those in favor have said makes eminent sense to me, and does not appear to be the mindless, drooling AB criticism that you pretend it to be. That's not nice. Some of the reasoning has been quite sophisticated and well thought-out. Seems that you can't acknowledge that.

OK, OK, public disclosure: I do live in Boeing Country, but I have plenty of problems with them, too, especially after they basically let MD take them over in a management coup. Mostly, all Boeing has done for ME is to keep me awake at night with their incessant engine testing. But I digress. [where's the dang belly-laugh icon???]

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 don't know that this was the case in this situation but it is an important factor that has to be born in mind. 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 big factor missing from the discussion is interpretation. If we take a direct signal and interpret it or misinterpret it, it takes time to correct and re-evaluate. In certain circumstances an audio signal is more reliable but as we know that also is subject to interpretation. The point is that using your instruments for example, instead of a yoke provides you with an organised initial frame of reference with graduated levels. Glancing at a yoke and trying to decide where it is when you are suffering say spatial disorientation can be remarkably misleading. What you see and what you think you see can be two different things - the banana experiment is very relevant here. A calm person will see something different to a panicking person.
Looking at your instruments will provide you with a much better indicator and what is more it will aid your interpretation because the initial frame of reference is already set - you don't have to judge to the same extent and importantly to create a frame of reference in which to judge. Evidence from the CVR indicates that the PNF was quite able to judge the situation as was the Captain (initially) but neither took the physical action necessary to override the PF.
This is also another reason why the yoke is a red herring - given the ineffective intervention by both non-flying members of the crew it is highly unlikely that their behaviour would have been any different had the aircraft been equipped with yokes. Short of direct physical intervention it seems that nothing was going to divert the PF from his actions but we must also factor in that incomprehension of the whole flight crew. I hold no brief for the side stick or the yoke but in this situation the type of input device is irrelevant.

"The type of input device is irrelevant..."

Erm, ok. What about its location?

What Instrument was the Captain seeing when he advised the PF to "Climb, Climb..." The PF responded, "But I have been climbing for some while...."

Thoughts? Any?

Subtle changes in terms of words, but major changes in terms of meaning. The exchange was actually:

It was the PNF that was saying "climb", immediately followed by a bunch of DUAL INPUT warnings. I think the Captain suddenly realised what had happened at this point.

Thanks, Dozy. So it was the two with you know, screens who could not decide what to do? PNF says CLIMB, (What was he looking at?), and the PF had already been "Climbing"?

Do you see a problem with what they both may have been seeing on the instrumentation? What was telling them to input Nose UP? Rather than a solution, Captain insists, "NO, No Climb." NOT, "DO THIS..." Instead, a command to do nothing.

They were all three privy to the only ticket home, the instruments.

How long had the a/c been so confused? YES, the a/c. The pilots and Captain are screaming that, they had NOTHING to go on of any value, OBVIOUSLY.

Three pilots in the weeds, but you say the a/c was "Doing as it was programmed...." How do you reconcile this?

A/C? "Nothing wrong, just three confused pilots". You kidding me?

Hi,

DW
DW
After that ..do you stay scotched on your first opinion (I was of the opinion that the PNF had a better handle on the aircraft's situation and as such, should have felt empowered to take control.) ?

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.

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.

Hi,

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)

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

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.

"I HAVE CONTROL" - no more - no less - no anbiguity
Forget your 'incredibly dangerous'

Only partially true - If a fight there is, both fighters could endlessly retake control.

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 ...

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:

Quote:

---

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?

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..

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.

Exactly! Some time ago someone (A33Zab, IIRC) explained that the stall warning stops because the ADR outputs AoA=0 when airspeed is <60 kCAS.

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.

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.

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

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.
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.
.

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.

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.

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.

Excellent post NARVAL! EXCELLENT

NARVAL
 

Wise words from a wise pilot.....

thank you sir!

franzl

dual input
 

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.

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.

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

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.

Please see your PM inbox.

Ok thanks HN39, I think that is the post ?
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 ... ?

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

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

]

Dozy (re: #201)
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)
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 ;)

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

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:

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.

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.

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.

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.


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.

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.

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.

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?

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


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!