AF447 Thread No. 3

[BluJet]

@sensor validation
No, I was only challenging takata.
I am definitely with PJ2 and Lemurian. Only at one point

Lemurian wrote
"That means that the captain must be at his LHS for T/O and LDG. Which makes him take in 99% of the flights the middle slot."he was mistaking, but this was corrected by PJ2 already.

We dont know for sure yet whether the captain took his seat again, but also for reasons explained earlier, I very much doubt.
This leaves me with:
LHS relief FO 4400 hrs on type
RHS FO 800hrs on type
3d occupant captain 1700hrs on type

[paull]

Purely a ball park guess - if a correct attitude change had not been made by 20,000 ft it would be a done deal.

So , anyone else care to suggest a number, because it has a bearing on crew actions. Some people are saying "how come they did not catch on in over 3 mins", well perhaps they did, lets just say you are descending through 20'000 at 10'000fpm and have two options;
A- stall, pretty sure it is, but (according to BOAC's SWAG) it is too late.
B- A dive, pretty sure (now) that it isn't but it is NOW the only recoverable option so I better go with it.

Persisting with a bad choice is sometimes the only option you have no matter how slim. It may well be guys that you only get one shot at this. I think they were dealt a real bad hand.:(

[jcjeant]

Hi,

Business Week : (another "official leak")

Air France Crew May Have Faced Baffling Data in 2009 Crash - Businessweek (http://www.businessweek.com/news/2011-05-28/air-france-crew-may-have-faced-baffling-data-in-2009-crash.html)

"The data and cockpit voice recording suggest the pilots never realized that the plane had stalled, BEA Chief Investigator Alain Bouillard said in an interview.

“They hear the stall alarm but show no signs of having recognized it,” he said. “At no point is the word ‘stall’ ever mentioned.”"

[PJ2]

...is there a distinct display for the pilots when the plane is actually stalled rather than facing an imminent stall? If not, wouldn't that be a worthwhile addition to the software?
JD-EE;

Couple of points for discussion:

The "stall" isn't as demarcated a break-point as it may seem. A wing, especially complex designs such as the A330 (and most other transports) does not stall "all at once", (this is by design), nor does it necessarily stay in a stall. In fact I don't think this stall could be defined as a "deep" stall in the way that Davies meant it in his book, but that's another rabbit trail.

The PFD [Primary Flight Display...horizon, speeds, altitudes, heading, vertical speeds, autopilot modes, etc] speed scale provides very clear information on those speed regimes approaching the stall, (photo of a PFD "at alpha-max", not yet in the stall, below) and, if the speed is available, provides sufficient information for crews to keep themselves out of that regime.

http://www.smugmug.com/photos/1112472528_TbaKx-M.jpg



Many here have advocated an AoA indication be provided among the standard displays, probably on the PFD. I have flown aircraft with AoA (B727) and like the idea and believe a sufficiently detailed discussion about the desirability, technical viability, reliability and certification of such indications is needed. The problem is made quite complex by broader factors and priorities such as the industry's approach to training and standards in re the use-and-abuse of automation, flying and problem-solving skills, etc. The broader question always is, Do we design more fences and interventions? Just because we can, should we?

Some very respectable observers have said in response to the question, "yes, we design more automation". I am not in disagreement with that view.

But it is not easily, nor simply discussed and settled. What is meant by "more"; how is it to be designed, certified, implemented, trained?

Already, the industry is discussing automated responses to TCAS and EGPWS events and tail-strike automation is already a reality on long-body aircraft. Clearly, those two interventions alone are extremely complex but not at all impossible to do.

An automated response to the stall? Again, not impossible - the question absolutely requires much discussion between many interested parties. I'm sure that discussion has been underway in some venues already. For basic starters, one has to define "stall", and when the intervention takes over and when it hands control back to the pilot.

The interesting comment has been made about resisting automation may actually "cause" more automation. I think that's okay. There is no resistance to automation in any of the comments that I've made. I've always advocated training (and getting into the books) to achieve a solid comprehension of one's airplane. (The balance between adhering to SOPs, and diverting from SOPs through one's 'understanding' of the airplane is a perrennial problem...not easily solved...how much "initiative" does the industry give pilots, how much do they stay away from trying things?...big questions, very relevant today).

My strong and consistent resistance is to the idea that we, (and our managements, the regulator, the safety people), can relax because of automation. THAT, to me is the problem.

The problem is driven by money, politics, convenience (of hiring/training) and the industry's spectacularly high level of safety, (which I believe is being taken for granted by newbie managers who have no idea of history and how the industry's safety record was achieved).

To your question, I'm not an aeronautical engineer so cannot explain the two questions you're asking: 1) What are the actual dynamics of the stall in a large transport aircraft?, and 2) How, in practical terms, might "the stall" be displayed to the pilots in such a way as to provide unequivocal guidance, in very bad circumstances, (weather, system failures, etc) for manual pilot recovery.

Perhaps HN39, or gums, Graybeard, Machinbird, Chris Scott and others can discuss the questions - HN39 and I had a great discussion about AoA on the second thread and I learned a LOT about the A330 and high-altitude stalls. Presenting the information swiftly, accurately and in a way that clearly shows trends either way, are fundamental requirements.

It has to be understood and accepted that the design and certification of such a system are monumental tasks, and that the questions are being asked within the context of other possible solutions to the problems outlined and discussed on this thread. Choices would need to be made as to which solution is best. Such decisions are by no means solely informed by the "flight safety" discourse and the moral question.

[sensor_validation]

...BEA Chief Investigator Alain Bouillard said in an interview...

Where/when? We'd all like to read about everything he said!

[jcjeant]

Hi,

Where/when? We'd all like to read about everything he said! Those people have the answer to your question:
Mary Schlangenstein and Mary Jane Credeur

An automated response to the stall? More simple a automated system for avoid stall condition ?

[galaxy flyer]

EDLB

How much G would be available for the dive recovery, if they had broken th stall in ALTN LAW?

[wiggy]

Interesting post.

An automated response to the stall? Again, not impossible - the question absolutely requires much discussion between many interested parties. I'm sure that discussion has been underway in some venues already. For basic starters, one has to define "stall", and when the intervention takes over and when it hands control back to the pilot.

Indeed...I wonder how any such proposed automated solution, if it is being postulated, would handle something like a stick shake at rotation due to LE's retracting (e.g. BA 747 at JNB not that long ago) ........

[spagiola]

Originally Posted by jcjeant
...BEA Chief Investigator Alain Bouillard said in an interview... Where/when? We'd all like to read about everything he said!

jcjeant did provide a link, see his post (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-101.html#post6487274).

This is the second BEA-attributed statement today, after the one in Flight. It seems BEA may have realized that their Friday report may not have had the effect of dampening speculation that they hoped it would.

[Graybeard]

If there were a fatal flaw in any component, hdwe, sw, or training, it would not be revealed until the fix was ready. The last thing the world needs is grounding of 1,000 airplanes until a fix for a once-in-ten-year event is found, thoroughly tested and implemented.

Meanwhile, if the above were true, the pilots would have to take the heat.

[takata]

Hi Blujet,

This leaves me with:
LHS relief FO 4400 hrs on type
RHS FO 800hrs on type
3d occupant captain 1700hrs on type
As it seems that we are in agreement about where was seated the relief pilot, I would like to understand what makes you to believe that the RP was FO1 (4400 hrs)?

Edit: see PJ2 answer to Lemurian, they both agree to the opposite:
- In all certainty, the operation of this flight was performed by a senior F/O seating on the RHS with command functions and a junior F/O seating on the LHS with basic radio-com and navigation duties, along with some minor engineering duties.
Agree.

[BOAC]

Here's another hare to start running. From Der Spiegel, I believe:

"Just over a year ago, Hüttig recreated the Air France crash in a flight simulator. In the course of the exercise, Hüttig noticed a strange anomaly in the plane's reaction once it goes into a stall. The trimmable horizontal stabilizer, a flap instrumental in keeping the plane on an even keel, automatically adjusted to push the nose of the plane skyward. Hüttig, a former Airbus pilot himself, and other pilots present for the test were unable to push the nose of the airplane down and thereby escape the stall.
When the BEA released its preliminary report last Friday, Hüttig immediately zeroed in on data relating to the trimmable horizontal stabilizer. During the final minutes of flight AF 447 as it plunged toward the Atlantic, the flap moved from a 3 degree deflection to a 13 degree deflection, almost the maximum possible. "The phenomenon is startlingly similar," he told SPIEGEL.
A Quiet Reaction
Hüttig passed along his simulator findings to Airbus, the European Aviation Safety Agency (EASA) and to BEA. On Oct. 27, 2010, Hüttig received a response from EASA which said that Hüttig's theory was inconsistent with the "current state of knowledge." "We suspect that the anomaly you found originated with the simulator you used in the study rather than with the airplane model A330," the response read.
Hüttig and Jeinsen told SPIEGEL that the data recovered from the wreck of flight AF 447 would now seem to have corroborated the simulator findings. Furthermore, Airbus has quietly reacted to the safety loophole. In a communiqué to airlines, Airbus provided a new version of pilot instructions for dealing with a stall. Furthermore, in the January issue of its internal safety magazine, there is a mention of manually trimming the horizontal stabilizers.
In response to a SPIEGEL query, Airbus rejected Hüttig's theory."

Hey ho!

[lomapaseo]

Greybeard


If there were a fatal flaw in any component, hdwe, sw, or training, it would not be revealed until the fix was ready. The last thing the world needs is grounding of 1,000 airplanes until a fix for a once-in-ten-year event is found, thoroughly tested and implemented.

Meanwhile, if the above were true, the pilots would have to take the heat.




Agree:ok: ..... mostly

It's too late to make the aircraft fly itself. It can be flown safely if one knows how even with an unexpected disconnected AP. Now how should we address the problem?

me thinks the pilots should not be held responsible to solve this problem

[PJ2]

wiggy;
I wonder how any such proposed automated solution, if it is being postulated, would handle something like a stick shake at rotation due to LE's retracting (e.g. BA 747 at JNB not that long ago)
And all other combinations of such events...it is an exceedingly difficult problem with which to come to terms, and really, when we come to thinking hard about it, the "goal" is informed by "mistakes and avoiding them" in more complex, crowded systems, (transportation), and therefore is to supplant human perception and response under the heading of avoiding "human error" for the purposes of commerce. Training and experience go a long way but so do error-trapping habitual behaviours where it is assumed that at each "fork in the road" so to speak, one "will" make a mistake, and so a form of "recursive" behaviour (constant revisiting of decisions/actions - not "second-guessing" but quietly, constantly confirming/re-affirming "normal"). It works for error trapping but not for system faults and emergencies, where SOPs, training, memorization and simply knowing one's airplane are irreplaceable responses.

The discussion on automation interventions is first, philosophical, and that does not mean merely specifiying and quantifying techniques but examining cognitive processes and the assumptions underlying the philosophy of mind. This won't go over well here I know, because this is a Tech Forum, but all that can and has been done in the name of "technique" and "automation", rests upon such assumptions about perception, response and cognitive processes whether we choose to examine them or not. I think it is better to examine them and know upon which basis our choices are being made in terms of system design, but one person ain't going to change policy.

Graybeard;
...until a fix for a once-in-ten-year event is found, thoroughly tested and implemented.Absolutely spot on.

[HazelNuts39]

When looking into the aerodynamics corresponding to the 'TE plot' I posted earlier, it became apparent that the tentative trajectory demanded load factors that exceed the maximum lift capability after 2:11:10.

TEplot2 (https://docs.google.com/leaf?id=0B0CqniOzW0rjZWNjMzNmZDAtNTk3Yi00NWQzLTlkYjctZGQ0Yjk 2Nzk4ZjE5&hl=en_GB&authkey=CMjmmEw) shows the revised trajectory and speeds.

TE_Angles (https://docs.google.com/leaf?id=0B0CqniOzW0rjOWMyNmQ3ZTEtZWM5Zi00N2Q5LTg1YmYtMzY2YjM wZmRlMWU1&hl=en_GB&authkey=CKOB-7IL) shows the corresponding angles of attack and pitch.

(With all appropriate caveats)

[Clandestino]

How much G would be available for the dive recovery, if they had broken th stall in ALTN LAW?

Provided everything works as advertized, 2.5 G.

[BOAC]

Here's another hare to start running. From Der Spiegel, I believe:

"Just over a year ago, Hüttig recreated the Air France crash in a flight simulator. In the course of the exercise, Hüttig noticed a strange anomaly in the plane's reaction once it goes into a stall. The trimmable horizontal stabilizer, a flap instrumental in keeping the plane on an even keel, automatically adjusted to push the nose of the plane skyward. Hüttig, a former Airbus pilot himself, and other pilots present for the test were unable to push the nose of the airplane down and thereby escape the stall.
When the BEA released its preliminary report last Friday, Hüttig immediately zeroed in on data relating to the trimmable horizontal stabilizer. During the final minutes of flight AF 447 as it plunged toward the Atlantic, the flap moved from a 3 degree deflection to a 13 degree deflection, almost the maximum possible. "The phenomenon is startlingly similar," he told SPIEGEL.
A Quiet Reaction
Hüttig passed along his simulator findings to Airbus, the European Aviation Safety Agency (EASA) and to BEA. On Oct. 27, 2010, Hüttig received a response from EASA which said that Hüttig's theory was inconsistent with the "current state of knowledge." "We suspect that the anomaly you found originated with the simulator you used in the study rather than with the airplane model A330," the response read.
Hüttig and Jeinsen told SPIEGEL that the data recovered from the wreck of flight AF 447 would now seem to have corroborated the simulator findings. Furthermore, Airbus has quietly reacted to the safety loophole. In a communiqué to airlines, Airbus provided a new version of pilot instructions for dealing with a stall. Furthermore, in the January issue of its internal safety magazine, there is a mention of manually trimming the horizontal stabilizers.
In response to a SPIEGEL query, Airbus rejected Hüttig's theory."

Hey ho!

[grity]

HazelNuts39 .... it became apparent that the tentative trajectory demanded load factors that exceed the maximum lift capability after 2:11:10....thats the pancake at 2:11:30 with 3 deg pitch and vz=-10000fpm

[JD-EE]

jcjeant, it may be appropriate to define how you are using fault.

If the PF caused the crash it does not automatically follow that "He is at fault."

Why did he do what he did? If we isolate a training deficiency, a software deficiency, or some other deficiency then while the PF may have caused it he is not at fault for it.

several others, the PF was apparently the 38 year old co-pilot with over 4400 hours on type and a license allowing him to take over from the captain. The 32 year old co-pilot did not have a license to take over from the captain. He did have 807 hours on type. So my reading of this data from the June 2009 Interim Report suggests strongly that PF was the older co-pilot.

Of course, I'm not ready to "blame" either one of them, yet. It appears the cockpit crew may have reacted correctly per training and manuals and had an experience that contradicted that training.

I also note plaintive requests for experience flying ALT2 - I wonder how often A330/A340 aircraft fall into ALT2, how often they train for it, and, in only a semi-serious tone, is ALT2 survivable? It is apparently rare. (And, yes, some people appear to have survived it.)

[Jazz Hands]

Some people here are missing a very fundamental point regarding the BEA release.

Its job was to give up just enough information, about a story of massive interest, to satisfy the general media - who will then go off and write about other stuff.

To suggest the BEA release contained every scrap of new information, and that it couldn't possibly give out any more to specialised aerospace journalists who know what they're talking about, is ludicrous.

And suggestions that professional journalists should shut up and just regurgitate press releases, instead of having the savvy to ask for those additional bit of information - the bits which the daily-rag press isn't interested in - is the sort of nonsense which doesn't belong in a sensible discussion.

[Rockhound]

Can we settle this question of who was PF and which seat he was occupying?
According to press reports, the junior FO (800 hrs on type) was PF, having been designated as such by the captain. But where does this idea come from?
According to BEA's 27 May update, "at 0155 the Captain woke the second co-pilot and said '[...] he's going to take my place'".
The 'second co-pilot' presumably was the junior FO.
Who was 'he'? Presumably, it was the junior FO and it seems highly likely that he was going to physically take the place of the captain in the LHS. However, that does not necessarily mean that he was PF.
I would instinctively think, as they were approaching an area of turbulence, the captain would designate the more experienced, senior FO (4400 hrs on type) as PF.
Yet, one minute before they impacted the sea, "the PF said 'go ahead you have the controls'. It seems unlikely that a more experienced pilot would hand off to a less experienced one.
So I would think the junior FO was PF and the senior FO was PNF.
Of course, there's also the possibility that, after he returned to the flight deck, the captain changed places with the senior FO in the RHS...but that's hardly likely.
I suppose the question can easily be settled by the BEA.

[Isobars]

No AB exp hence the question.

What does the FD give if TOGA is selected at altitude ?

On our current bird one gets standard pitch up and wings level as default. All other lateral modes are canceled.

One then sees time to time (in the sim), if the trainees forget to select a lateral mode after TOGA selection and follows the FD, a constant deviation of course if there is some assemetric present that looks pretty similar to last track of AF.

[Rockhound]

The 32 year old co-pilot did not have a license to take over from the captain. He did have 807 hours on type

JD-EE,
Would the junior FO not allowed to have been PF? After all, he was qualified to operate the A330, just not as PIC.

[sensor_validation]

Hi,

Those people have the answer to your question:
Mary Schlangenstein and Mary Jane Credeur

And what makes you think the French BEA chief spoke to these two Americans? They did have help from 3 staff in Paris that is closer to the BEA offices - but the article also contains other unattributed 'facts' that are not confirmed by the BEA statement i.e. who was at the controls when so don't believe all you read on the net, and this conflicts with other leaks "from sources close to the investigation" that were reported in Australia!

The CNN report Air France crash pilots lost vital speed data, say investigators - CNN.com (http://edition.cnn.com/2011/WORLD/americas/05/27/air.france.447.crash/index.html?iref=mpstoryview) basically repeats the BEA report correctly, but the pilot journo Miles O'Brien reliably informs "You push down on the wheel to gain air speed"- nuff said.

[PJ2]

JD-EE;
I also note plaintive requests for experience flying ALT2 - I wonder how often A330/A340 aircraft fall into ALT2, how often they train for it, and, in only a semi-serious tone, is ALT2 survivable? It is apparently rare. (And, yes, some people appear to have survived it.)
From experience and from the paucity of responses regarding Machinbird's request for "Alternate Law" (1 or 2) experience, it is indeed a very rare event.

Alternate Law itself, like Direct Law are, (or certainly should be for A320/A330/A340 crews), non-events, especially if one is accustomed to and has practised one's craft by manually flying the machine.

Notwithstsanding 'only partially-serious', talk of "survivability" is like saying is walking down an escalator that isn't functioning "survivable", or crossing the street without traffic lights? These things do have risks associated, but one simply responds appropriately.

To pilots new on the airplane it would take a few moments to get used to the directness of the controls but it would be nothing they wouldn't be familar with from earlier, conventional controls say on the B737.

There is no mystique, no mystery about this "Alternate Law" thing...and if we think about it, no airliner would ever be certified if such reversions were difficult to control or had a propensity to diverge into unstable flight.

These are fundamental design and engineering notions and expectations. In Direct Law, (not the case here), the airplane has all flight controls with NO failures. The pitch trim is manual and in the simulator at least, one simply trims the airplane the way its always done with conventional flight control systems.

All control "feel" in the control column is, and has been for fifty years, artificial feel which is "built into" the system to approximate the feel of the need to trim...there is NO direct feedback from any flight controls on any airliner flying today that provides feedback to trim the aircraft. It's usually done with springs and whatnot.

On the A330, when flying in direct law, one must be careful with the rudder, (due no limitations) and one must trim the aircraft - to do that, one simply rolls the hand wheel fore or aft to trim out the forces, just like one did on the B727 or DC8...trim...wait...trim...wait, etc. There is rudder trim but no aileron trim.

Every simulator session I've had, has practised Alternate Law due to various system failures which we practise. Once in a while with a dual hydraulic failure or the emergency electrical config the aircraft reverts to Direct Law. Again, it is a non-issue.

In certification work by the FAA, the A320 as been flown and landed using only differential engine thrust and only manual trim...not using the stick at all. I've done that in the sim on the A320 as part of the initial check-out on the airplane...you can land the airplane on trim...its a mess but that is where I would use the term "survivable".

That can't be done on the A330/A340...too much mass, too difficult to anticipate pitch changes and the exercise becomes an out-of-sync PIO until the "firm" touchdown or other such "arrival".

[Clandestino]

Can we settle this question of who was PF and which seat he was occupying?Untill we get sidesticks displacement plots, no.

[Lonewolf_50]

PJ2:

A point on cognitive factors, raised by ECAM Actions on the other thread.

http://www.pprune.org/rumours-news/447730-af447-wreckage-found-63.html#post6487657

In short, Low Speed Stability in pitch channel Alt Law may be trying to move the stick one way (senses slow speed from FUBAR AS system) which is nose down. This can be overridden by the PF pulling ("back stick") the other way, which could have been overridden by a bit too much force initially?

My idea, perhaps dead wrong, is an initial reaction was response to that perceived stick load (nose down) with an overcorrection (see 7000 FPM zoom climb) initially corrected to 700 fpm climb ... but that doesn't answer all of the mail. Given my own experience in flying out of trim aircraft (now and again in ham fisted fashion) I can see how this might play out.

What my own instrument flying experience -- both my own episodes of making a hash of flying on instruments, and watching pilots under instruction or on a check ride do similarly -- tells me is that if that feel was a factor, an inextricably linked factor is (I am on the cognitive theme here) likely a scan breakdown away from primary scan instrument -- attitude indicator (artificial horizon) -- early in the event. All my previous posts down rabbit holes of partial panel and tumbling gyros aside (sorry about all that) it is isn't that uncommon in instrument flying, even with a working attitude reference, for cognitive mismatch to occur when tasks and stimulations add up. (Aside: playing the SOB sim instructor allows you to find any pilot's task saturation point. *Insert Evil Cackle here :E*).

Since we don't know what he was seeing, and apparently can't from the way FDR data is recorded ... how can one get to the root cause of his control inputs? :confused:

[PJ2]

LW_50...yeah, that's a big displacement to be accounted for by that response from the AFS...hm. Another research item but just heading out...I'd have to ask the question whether or not the AFS would behave that way in Alternate 2 Law. I don't think so, but will take a look when back. PJ2

[JD-EE]

HN39, your plots make sense to me with regards to AoA. If, as has been shown, the plane hit with approximately equal forward and down velocities the AoA for a dead level plane (0 degrees pitch) would be 45 degrees. So I'd think the AoA would have gone up over 50 if the plane hit with a pitch of 16 degrees up even with a head wind.

Your data makes good sense for "what". That still leaves why, which apparently has BEA puzzled, too.

[SaturnV]

Tim Vasquez has updated his meteorological analysis, dated June 1, 2011.

Air France 447 - AFR447 - A detailed meteorological analysis - Satellite and weather data (http://www.weathergraphics.com/tim/af447/)

This study was significantly updated on June 1, 2011 in memory of the 2nd anniversary of the crash. Also it was precipitated by the renewed interest in the fate of the flight with the data recorders having been recovered a few weeks ago. Interestingly it appears that almost all of the conclusions in my earlier study were correct. The purpose of this update is to introduce some new information, make corrections where necessary, edit extraneous theories that can now be disregarded, and clean up the text a bit.

[RealQuax]

@ rgbrock1: have you ever yourself experienced pitot tube icing and, if so, what happend and how did you react?

No. only some spurious A.ICE pitot and static-warnings while passing cloud layers (me thinks: heating momentarily overwhelmed). Just worked though the ECAM-procedure, but it cleared every time on its own...

[wiggy]

"at 0155 the Captain woke the second co-pilot and said '[...] he's going to take my place'".
The 'second co-pilot' presumably was the junior FO.

Not necessarily, the transcript says "le commandant de bord réveille le second copilote" which seems to me to read he woke the second, or other P2.

So reading the BEA transcript it's quite possible that the junior P2 was in the RHS from takeoff. The captain woke the other (or second) co-pilot by some means and then commented to the junior pilot in the RHS that:"he's going to take my place". i.e. the senior P2 simply replaced the captain in the Left hand seat.

[Meikleour]

Graybeard: It certainly was investigated! Aug 1995 and resulted in the fitting of pitot heads with increased heating and a software change to increase the time line before ALT2 was latched. A/P and ATHR initially lost but were restored once out of icing conditions however the lateral twitchy aileron response was very evident for the landing.

[MartinM]

wiggy wrote:

So reading the BEA transcript it's quite possible that the junior P2 was in the RHS from takeoff. The captain woke the other (or second) co-pilot by some means and then commented to the junior pilot in the RHS that:"he's going to take my place". i.e. the senior P2 simply replaced the captain in the Left hand seat.


BEA says AP2 was active. PF must have been sitting on the RHS :)

[JD-EE]

Rockhound - I read that handover as one thoroughly confused pilot deferring to the other who might have a fresh idea. (Of course, if the surface had come into view, somehow at night under a heavy storm, with the Moon set or very nearly set, your view makes more sense.)

[Clandestino]

Since we don't know what he was seeing, and apparently can't from the way FDR data is recorded ... how can one get to the root cause of his control inputs?By sitting on one's hands and refraining from extensive theorizing until such time when BEA releases DFDR plots and CVR transcript. From DFDR data we can 99.99% reliably conclude what were the indications in the cockpit. 0.01% refers to freak CRT (or LCD) failure undetected by ECAM.

[RealQuax]

@MartinM: The plane flies like a charm with the PF in the RHS on AP1: It is just a procedure to use the onsite-a/p. In my company for instance, in MNPS-airspace flying with CPDLC, procedure is to fly on AP1, irrespective of who is PF.

[JD-EE]

Clandestino: Quote:
Originally Posted by Rockhound
Can we settle this question of who was PF and which seat he was occupying?

Untill we get sidesticks displacement plots, no.

I'm starting to mumble to myself we haven't a clue where either of the two co-pilots was sitting. Was takeoff captain and 37 or captain and 32 unless 32 was not licensed to take off the plane with captain sitting in the left seat.

There is no record yet released saying PF in right seat handed off to the new person who moved into the left seat. So it appears the person at the controls as the plane upset was the person at the controls for basically all of the flight.

We do have a lot of news report "assumptions", "presumptions", and rumors. But I discount that.

[MartinM]

I just had a chat with one of my Bus driving colleagues. Let me drop in one of his ideas.

Highspeed stall at FL350

Pilot reaction would be. Pitch up to reduce turbulences over the wing. This reduces speed of course and pitches up momentarily till you begin to enter into low speed stall. If you get a too high AoA at that point, you may generate an unrecoverable deep stall.

This would somehow explain, why the PF initially pulled the stick, then did some nose down to slow down the vertical speed. And unfortunately it ended up in a deep stall.

Which immediately would have required throttle IDLE and THS to 0°

BEA report says that IDLE throttle was much later at around FL100

What do you think on this theory?

[fantom]

No, on several counts, I don't think so...

[jcjeant]

Hi,

JD_EE
jcjeant, it may be appropriate to define how you are using fault.

If the PF caused the crash it does not automatically follow that "He is at fault."

Why did he do what he did? If we isolate a training deficiency, a software deficiency, or some other deficiency then while the PF may have caused it he is not at fault for it.Methink you don't read this or forget it when answered

But I'm sure it will be not so straight ... and certainly it will be recommendations about the pilots and airline (training SOP .. etc...) and recommendations for the constructor(s) and recommendations for the regulators
Seem's to me a usual and honest scenario and it will be no different for the AF447 case.
So .. it will be also many food for the court of justice
Nobody will go out white from this accident. Do you agree ?

[3holelover]

With absolutely all the due respect I can muster... I think, Martin M, as a Microsoft ONLY "pilot" ... it's probably time you let folks who know a thing or two, do the talking. I suspect when some of the posters here realize you've misled them in your "current a/c- A330-A340", and actually only had your MS flt sim time, they might be rather disappointed.

[Clandestino]

Highspeed stall at FL350

What is highspeed stall?

Mach buffet is not stall!

As for the your colleague's theory, IAW Sturgeon's law, it's as valid as at least 90% of theories regarding AF447 put forward on the PPRuNe.

[Lonewolf_50]

Since we don't know what he was seeing, and apparently can't from the way FDR data is recorded ... how can one get to the root cause of his control inputs?

By sitting on one's hands and refraining from extensive theorizing until such time when BEA releases DFDR plots and CVR transcript. From DFDR data we can 99.99% reliably conclude what were the indications in the cockpit. 0.01% refers to freak CRT (or LCD) failure undetected by ECAM.

In a word, no.

Are we reading the same thread? We are on its third bundle of posts.

What is clear is that the BEA has on their record from the FDR the indications for the Left Seat pilot, but not for the Right Seat pilot.
The question I asked is
What was the PF seeing?

It is more likely that the CVR will give more clues.

Unless what has been posted is wrong, the FDR does not record what was on his display.

But that isn't even what I am asking, Clandestino.

You spend much time flying?
I think so.
You familiar with a scan pattern?
I think so.
You use one?
I think so.
You spend much time teaching people how to fly?
I don't know if you have, but I have.
Try your dismissive line elsewhere.

What the pilot flying was seeing is driven by his scan.
You assume that his displays matched the Left Seat displays. Fine.

Cheers.

[JD-EE]

jcjeant - I'm trying to avoid any assignment of fault at the moment. But, after oscillating around a fair amount I'm close to convinced the three cockpit crewmembers will come out clean in any rational world. It's looking like they followed their "programming" to the point of utter confusion. It's hard to blame them for not breaking out of the strictures of their training to solve the problem.

Aside from that I think there may be a system design problem and most likely there may be a training error. (This latter point has already been tacitly admitted with the revised recovery procedures.)

(wry chuckle) Reading the above some of the AirBus related leaks make a lot of sense. They don't have to do anything because it was already done. And the some of the software design issue has a training workaround. (The lack of a fully time air flow based AoA reading in the cockpit is confusing if AoA and thrust are the real recovery for transient icing issues.)

[aerobat77]

maybe- but of course like everything other its just a shot in the dark, the pilot was still believing in the protection systems and an not stallable aircraft and tried a recovery similar to a wind shear on an airbus- full upstick and toga ,maybe truly believing he is in a massive downdraft and not a stall.

why he initially climbed and tried not not keep power and pitch constant when he lost the indications will be a mysterium.

on a other hand we have to consider that discussing it is something other than finding itself in a big thunderstorm, when one system after another quits, being in live danger. maybe also he just quit mentally and his inputs were instinctive without thinking. who knows.

best regards

[CogSim]

Originally posted by SaturnV
Tim Vasquez has updated his meteorological analysis, dated June 1, 2011.

Air France 447 - AFR447 - A detailed meteorological analysis - Satellite and weather data (http://www.weathergraphics.com/tim/af447/)


Interesting take:
The flight was suspected to be within areas of showers and precipitation up until the time of impact, and the descent below FL250 into the critical -10 to -20 deg C zone probably involved some degree of clear icing on control surfaces, though it is uncertain whether this affected recovery of the aircraft, especially due to the short accumulation time that would be involved.

[Rockhound]

I'm starting to mumble to myself we haven't a clue where either of the two co-pilots was sitting.
JD-EE
Yeah, no kidding. That BEA Update is too ambiguous for anybody to come to a conclusion. The one thing we do know is that the PF on takeoff from Rio was one of the FO's. I don't see any problem with the junior FO doing the TO with the captain in the LHS.

Wiggy writes
The captain woke the other (or second) co-pilot by some means and then commented to the junior pilot in the RHS that:"he's going to take my place". i.e. the senior P2 simply replaced the captain in the Left hand seat
but that's all speculation. Who was the "other (or second) co-pilot"? We don't know whom the captain was addressing or who he meant by "he's going to take my place".

No doubt all (or most of it) will be revealed in due course. Still, it's strange - well, maybe not so strange - that the print media all proclaimed the "baby pilot" to have been PF.

[MartinM]

Sorry for going off topic

3holelover wrote:

With absolutely all the due respect I can muster... I think, Martin M, as a Microsoft ONLY "pilot" ...
If this is what you call MS FS A340, yes, then it is MS FS as you say ...
http://www.muehlemann-pix.ch/pics/DSC00228.JPG

I am sitting in RHS as the Side Stick I am used to, is always on the right and throttle on the left.

Have a good night

[PuraVidaTransport]

According to the first report from the BEA, it says that:
"The airline’s procedures(5) specify that to be a replacement duty pilot, a crew member must have the same rating as the crew member that he or she is replacing and, in addition, during the captain’s rest period, a pilot with the same license as the captain must be at the controls."
This tells me that 37yo F/O had to be at the controls because the 32yo F/O did not have the same license so was not qualified (according to AF procedures) to be PF while Captain was on rest break.
However, we can't be certain which seat he might have been flying from. Either of the two were qualified to be flying the plane with the Captain in the LC.
So, if the 37yo took off in the right chair, he would probably have still been there flying the plane at the time of the incident. If he was the Captain's relief, he was probably flying from the left chair with the 32yo in the right where he'd been since leaving Rio.

[aerobat77]

offtopic yes, and a nice full motion simulator.

[3holelover]

... and by your own admission, you have somehow managed to accumulate a grand total of 6 hours on that simulator.... :bored:....

Again, with all due respect, and with humble apologies, it hardly qualifies you for expert commentary. ...and most certainly doesn't qualify you to say you're "current on: A330/340"

I just felt those who actually took up a page of this thread debating issues with you might want to know.... with all the chatter that came, your confession was very quickly buried.

[forget]

3holelover With absolutely all the due respect I can muster... I think, Martin M, as a Microsoft ONLY "pilot" ...

3holelover. MartimM made it clear earlier on that he was directly involved with Level D A330/A340 Sims. An apology may get him back when his input could be very useful.

[paull]

I suppose some people are hoping to say, 'an inexperienced pilot made a mistake', so we can all sleep easy. Very tidy, sorry I don't buy it. Three qualified pilots were on duty and it still happened. I think we are going to see lots of learning from this, I just wish we had learnt from the previous cases where only N-1 holes lined up. Assuming you need 5 holes, at say 5% chance each then there should be around 95 cases where it nearly went wrong.

It is nice to see that this thread has calmed down a little, very few people are bragging that they would have called it right first time. Most of those who have come anywhere close to being qualified to claim "seen it, done it, worn the t-shirt", are showing great humility and might only be with us now thanks to ejector seats.

I am sure that Airbus will learn an enormous amount from this, and we will all be safer for it, a high price was paid, lets get value for money.

[Lonewolf_50]

3hole ... your exposing Martin considered:ok:, I am grateful he posted the picture.

It gives me some idea where one would NOT try and stick an AoA indicator, and a better sense of where relative to the LHS the ISIS is.

If that layout is mostly similar to A330 (is it, beyond the different number of engines controls ... ) then RHS cross-cockpit scanning the ISIS would make for a slightly awkward scan technique.

A nice little unintended outcome. :) Thanks to you both.

[lomapaseo]

3holelover


... and by your own admission, you have somehow managed to accumulate a grand total of 6 hours on that simulator.... http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/wbored.gif....

Again, with all due respect, and with humble apologies, it hardly qualifies you for expert commentary. ...and most certainly doesn't qualify you to say you're "current on: A330/340"

I just felt those who actually took up a page of this thread debating issues with you might want to know.... with all the chatter that came, your confession was very quickly buried.


let it go :=

No need to try and "out" people on a forum, simply debate the issue, some of us can interpret the rest :bored:

[3holelover]

let it go Roger that. Wilco.

[Clandestino]

Unless what has been posted is wrong, the FDR does not record what was on his display.

Good point, seems I've made one assumption too many, my apologies, sir. Can anyone confirm that "l'enregistreur de parametres" as fitted to AF 330s really doesn't record ADIRU2 (or ADIRU3) IAS output?

What the pilot flying was seeing is driven by his scan.
You assume that his displays matched the Left Seat displays. Fine.

Not quite. What display are you talking about? Speed or everything else on EFIS? If what's now just hinted gets confirmed in future reports, left and ISIS pitot unclogged at different times so there's no reason to think that right pitot was in sync with either of the two remaining. However there is no mention so far that any of the four attitude references tumbled or that ALT or VSI data got invalid at any time. Don't jump to any conclusion from that however. It will take much more than this "report" to have good idea what happened with AF447.

You spend much time teaching people how to fly?
I don't know if you have, but I have.
Very well, sir. May you long continue to do so and may you teach your students well. However, whatever, you, me or anyone else on this forum chooses to do as daytime job, it has no bearing on what happened to AF447.

What we know so far is very little. It is only natural to try to fill the gaps with some conjecture but this method hasn't historically proved itself to be accurate or useful.

[gums]

@ PJ

To your question, I'm not an aeronautical engineer so cannot explain the two questions you're asking: 1) What are the actual dynamics of the stall in a large transport aircraft?, and 2) How, in practical terms, might "the stall" be displayed to the pilots in such a way as to provide unequivocal guidance, in very bad circumstances, (weather, system failures, etc) for manual pilot recovery.- can't answer first question, so we need to have somebody who has gotten close to the edge or even exceeded it to tell us. I can't believe the 'bus aero is so great that some type of airframe vibration or buffet or slight wing rock cannot be present. Just my opinion.

From my experience with the full-time, automatic leading edge flaps in our little jet, stall was extremely benign. Traditional buffet/wing rock/etc. was greatly reduced, as the flaps were designed to help with. Also had better directional stability. Further, as with the 'bus, we were theoretically "protected" by our AoA limiter. So you never got to see an actual stall except the dreaded "deep stall", heh heh.

- Second question might be easier to answer, and 'bird's answer and that of the others should be interesting.

Display the AoA with respect to "stall" AoA in a straightforward manner. The display I see for the 'bus is confusing, and seems to show several points of interest. It also is embedded ion the speed display. The jet I flew with the most critical AoA was the VooDoo, and it had a big old AoA gauge with a needle indicating existing AoA and a brightly-colored needle showing where eagles dare to tread! That plane did not "stall", it pitched up and tumbled about all three axis. I can't believe the 'bus is so sensitive to AoA or a high speed mach buffet/control reversal/flutter that we need be concerned about a sudden and debilitating loss of control. And the AF447 data thus far seems to indicate that the plane can get into trouble in an insidious fashion that can be dealt with, but requires training and a good cross check.

But most importantly, the plane needs a flight control system logic that does not disregard AoA once the wheels are in the well. To disregard AoA if the speed sensors are FUBAR cracks me up. The doggone things were out to lunch to begin with, and may have only recovered some degree of usefulness at a much lower altitude. AoA fault recognition is not a difficult task for the computers, as AoA changes slightly with every pitch/gee change that the 'bus does every second or even millisecond, even in "Alt" laws. Hell, it's the AoA changes that the wings use to create those pitch/gee changes. GASP!

Secondly, a good HUD can show AoA even if the vanes/cones are frozen. The difference between pitch and actual flight path vector is AoA!!! ( wing chord incidence allowed for, naturally).

So while I am on my roll, a good HUD should be in every commercial airliner, even the small regional things. And I hope many saw the shuttle landing video last night, as it was the main TV video due to the night landing.

A good HUD need not be complicated, with many pieces of data presented. And it's easy to have "de-clutter" capabilities. It can provide no kidding velocity vector and attitude info as a matter of course. Speed, AoA, heading and such can be easily displayed as we saw last night with the shuttle display. Steering cues are a piece of cake. and the beat goes on...

Sorry for the rant, but I am upset with all the talk of who was in what seat, more weather data and press releases and such. The crash was the result of a sequence of events and human actions and aircraft characteristics, both aerodynamic and mechanical/computer-dictated, that resulted in a tragedy all here wish to prevent in the future.

and I'll edit later after I crawl off the wall ( remember, a fighter pilot is not drunk as long as he can hold on to a single blade of grass to keep from falling off the surface of the Earth!)

[promani]

lomapaseo
No need to try and "out" people on a forum, simply debate the issue, some of us can interpret the rest

Very mature advice. I concur.

MartinM
If you are learning to fly, then good luck to you. I hope you succeed. But do not take on the experts. Just concentrate on your flying lessons

Food for thought. Is there any connection with the FL increasing 7000f/m, then FL-10000 f/m, and Tim Vasquez's revised Met analysis?

[BluJet]

Hi takata,

sorry for the late reply
As it seems that we are in agreement about where was seated the relief pilot, I would like to understand what makes you to believe that the RP was FO1 (4400 hrs)?I think we agree but just to make sure: I think the RP was the pilot who was qualified to be in the L/H seat during the cruise part of the flight. We would need somebody of AF to clear this but as of to date I am thinking that a relief F/O takes the LH seat. A relief captain could take the RHS as well but this was not the case.
A pilot with 800 hrs does not have this LH seat qualification, so he was in the RHS and in this case, also PF.

Edit: see PJ2 answer to Lemurian, they both agree to the opposite:
Quote:
Originally Posted by PJ2
Quote:
Originally Posted by Lemurian
- In all certainty, the operation of this flight was performed by a senior F/O seating on the RHS with command functions and a junior F/O seating on the LHS with basic radio-com and navigation duties, along with some minor engineering duties.

Agree.
Sorry, I missed this part of Lemurian's post, but yes: I do not agree with that. The senior F/O needs to be in the LHseat. (I can hear future discussions already, where we will be told that a 3crew cockpit need to consist of at least two captains.)


@paull
I suppose some people are hoping to say, 'an inexperienced pilot made a mistake', so we can all sleep easy. Very tidy, sorry I don't buy it. I am not hoping to say anything. I am talking about facts. Fact is: PF had 800hrs experience on type. There were two other pilots with more experience on the flight deck. Would that help to improve the overall situation? DEFINITELY
Would it help if somebody of the more experienced pilots flew the aircraft?
I DONT KNOW
I feel more comfortable with some 10k+ hrs on 320/330 today as I was feeling with 800hrs. No grading, no qualification argument, just another fact.

Regards

[john_tullamarine]

What is highspeed stall ?

I'm sure that your question was tongue in cheek at the time.

However, for the discussion, at least two situations might be so described -

(a) a pitch up to an appropriate G-level can cause an accelerated stall. In effect, the wing sees a "heavier" aircraft due to the load factor and stalls at the higher speed. Handling characteristics may be considerably more interesting than for the normal certification stall.

(b) at very high pitch rates (as I recall from an RAeS report on the subject - in excess of something like 70 deg/sec) a quasi-stable upper surface vortex (a bit similar to the stall vortex on a delta) can see the stall angle pushed considerably higher than what we see for the normal certification stall. Generally not relevant to most fixed wing aircraft but, apparently, a problem in the rotary wing arena at times.

[gums]

Great points, JT the Moderator.

It could be that the term bandied about refers to mach effects such as I related from the Yeager discussion.

If we exceed the "critical" mach, we can see things like aileron reversal, nose tuck, flutter, etc. All these bad things due to the shock wave moving back along the stabilizer or main wing and preventing the normal control surfaces at the rear of the wing or stabilizer from acting normally.

Another way to get into trouble near the critical mach is to rapidly change your AoA. The shock wave will move along the chord of the wing and have the same results as exceeding the critical mach. This more closely resembles the "high speed stall" phenomena described by JT the Mod.

Unless you are driving a supersonic design, pulling back the power is usually sufficient, as you are already experiencing a lotta drag. If in a dive, that may not be enough and spoilers or other drag devices might also be required. As most airliners have swept wings, they are more tolerant of mach effects than the old straight wings, so I am not too worried about mach-induced control problems for the present scenario we are discussing/analyzing.

[Yankee Whisky]

I recently thought to try FSX simulator software (AB320) to see what would happen if I selected fully nose up trim and nose up elevator at cruise and reduced power to idle when reaching the top of climb. IAS starting was 250 kn. Autopilot OFF.

The AB320 climbed from 19000 @ 250 kn IAS to close to 37000 feet at around 38 degr nose up and went into a deep stall whilst starting rotating and changing bank angle. The height achieved is questionable, in my opinion even though full power was used to the top of climb..

Putting the trim fully forward (in clean configuration) produced no effect as well as nose down elevator. The aircraft remained doing scary gyrations around all axis.
Putting the gear down and flaps down produced no result with the trim at fully nose down and power at idle.

Putting the trim neutral and adding full power and nose up elevator caused the aircraft to leave the stall and dive to gain (excess) airspeed.

Again; this is (very limited) MS FSX at work and all I am trying to bring to the forefront is
whether there could have been a situation where "the book should have been thrown out the widow"? I seem to recall several instances where pilots did this and got out of desparate situations !

Although it is theorizing, what are your professional thoughts on this?

[bubbers44]

I'm familiar with mach buffet which I guess some people call high speed stall. It isn't a stall but supersonic flow over the wing when you are high and too fast. Low speed buffet at high altitude is when you get supersonic flow over the wing because of high AOA and the increased airflow over the wing. Flying the big jets explains it very well if anybody is interested. The book explains a lot that most instructors don't know. Things like why the IAS for stall increases with altitude. Never found the answer to that anywhere else.

[aerobat77]

Food for thought. Is there any connection with the FL increasing 7000f/m, then FL-10000 f/m, and Tim Vasquez's revised Met analysis?

i personally do not think there is a direct connection. for me it seems that the initial massive climb at this altitude resulted from pilot action pulling back the stick and using aircraft energy ( FL 350 and M 0.8 should result roughly in 270-280 KIAS) for this climb until the plane ran out of airspeed and stalled. the -10000 f/m are simply a more or less ballistic fall down with stalled wings.

two more things which here are discussed

1) a deep stall ( where the tail is in the shadow of the stalled wings and you have no elevator effect) should affect t-tail planes and the a 330 is another design. further it seems from the interim report that the pilot held the stick back most the time until impact so serious attempts for a recovery were not made.

2)the pitch up moment from applying TOGA. well, at FL350 the turbines are far away from developing the same thrust like at sealevel and so i doubt that pulling the levers forward from the CL notch gave here an significant additional pitch moment , especially that before this the engines were not idling but in cruise power.

best regards !

[PJ2]

bubbers44;
I'm familiar with mach buffet which I guess some people call high speed stall.
So...as per comments above and your experience, can the difference between Mach buffet, and stall buffet, be felt/determined? Your thoughts...would one know when one is in high speed or low speed buffet?

I've felt high speed once, very briefly, and it was "sharp". I haven't felt low speed, at high altitude except in the sim and I don't think the sim experience, (Level D sim) is valid beyond "normal".

[john_tullamarine]

mach buffet which I guess some people call high speed stall

No really. What gums is talking about occurs somewhat about the onset of initial buffet. Not a stall, per se, but does involve flow separation and certainly can result in an upset - similar result for the pilot, I guess.

Low speed buffet at high altitude is when you get supersonic flow over the wing

You might like to go back and re-read up on this one ? Lowspeed buffet is normal prestall buffet. Highspeed buffet is the onset of shock wave related flow problems. Mind you, at normal cruise levels, the two might not be separated by a large range on the airspeed side of things.

Things like why the IAS for stall increases with altitude. Never found the answer to that anywhere else.

One should find this in most of the basic books covering aerodynamics

[aerobat77]

well, beyond the fact that a laminar flow wing may stall with little or no buffeting i doubt anybody can answer how a mach buffeting and low speed buffeting feels in an a330 since on the one hand in normal law the airplane ( as well your company :O) does not allow such situations and on another hand every pilot tries to keep away from this. i think we can agree that stalling a widebody is a very serious situation and something other than a cessna 150. surely the pilot of af 447 had other problems than feeling into mach or low speed stall buffets.

[Graybeard]

Didn't I read on these pages that the AB get away with relaxed stability, whatever that means, rather than positive stability, due to advanced stall protections?

Brain starting to smoke - gotta' go.

[JD-EE]

Rockhound, do be aware that the BEA's job is to diagnose what went wrong and recommend any required changes in procedures or hardware to make flying even safer. They are not chartered to find blame. So remaining ambiguous avoids the blame game.Personally I think that was quite wise of them. (Compared to when I was a child air safety is outrageously unbelievably good. But, nothing is 100% even though that is a laudable goal towards which one should strive.)

[3holelover]

"in two minutes we should enter an area where it’ll move about a bit more than at the moment, you should watch out" and he added "I’ll call you back as soon as we’re out of it".

They were clearly expecting some "buffeting", so isn't it likely that any stall buffeting they felt, when combined with a "what's it doing now" a/c that seemed to be seriously misbehaving, would have been missed, or misinterpreted?

I was once the best damned VW Beetle mechanic I knew... but then I got one that was fuel injected and it had a computer, and lots of sensors.... whenever anything went wrong with that thing I almost always thought it was the computer fouling things up... and it rarely was.... I was almost useless with that machine.

...point being, I think it's entirely possible that the PF was under the illusion that, since his airspeed was u/s, and other things didn't seem to add up -- how come when I pull back on the stick I don't feel my body being shoved into the seat? -- the PF said "I don’t have any more indications", and the PNF said "we have no valid indications"..... the "what's it doing now" airplane must be badly fouled...

Given the 30 seconds of aft, left stick he'd held at one point, it would certainly seem he must have been acutely aware of some kind of an apparent disconnect between his actions and the ship's response.

[Machinbird]

This is a possible explanation of the AF447 pitch up from FL350 to FL380. This is theory or speculation at this point. I believe the pitch up was inadvertent, was caused by difficulty in managing roll angle which task overloaded the PF to the extent his scan broke down.

Before you exclaim "Poppycock" or BS or whatever, let me set the probable reasons and scenario.:}

First, lateral control in the bus would normally be done with the fingertips and with small motions of short duration. The normal roll rate depends on deflection from stick centered for both Normal law and Alt 1 Law. Normal law would command a rate of 15 degrees/ sec with full deflection and Alt 1 is "similar to normal law" except you lose spiral stability.

When you get to Alternate 2 law, things are quite different in the lateral axis. Control surface deflection is directly proportional to control deflection-period. No turn coordination with the rudder. No roll limits, you can roll without the bus fighting you. If the aircraft is in balanced flight at this point, no big deal. Probably just a little bit more twitchy than you are used to. Maximum roll rate is now 20 to 25 degrees per second depending on speed and configuration.

The problem comes when you are not in balanced flight. Suppose the rudder changes its trim point in the switch to Yaw alternate law (this may be a function of rigging of the control system.) The effect of this is that your lateral zero roll position now changes to a point not in the center of the lateral travel, and you have to exert force to hold it there.

How much force?
For the A320 from a 2004 post by 'Max Angle'
Quote:
The figures copied from an Airbus publication and converted from horrid Euro units to pounds are:

Breakout force: 1.1 pounds

Pitch: Fore and aft. +/- 16 degrees 22.5 pounds

Roll: Outboard 20 degrees 5.6 pounds.

Roll: Inboard 20 degrees 7.8 pounds.

Note that the force is different for inboard and outboard roll. Airbus found during development that your arm is stronger moving inboard than outboard and fine tuned the forces to make left and right roll feel the same. Try moving the stick left and right holding it from above next time you are at work, you can clearly feel the force difference. I have to imagine that the A330 stick is almost identical. They do want an easy transition from one aircraft to the other after all.

What does this mean to lateral control? It suddenly becomes very difficult. Yes 7.8 pounds isn't that much force, you can hold that with one finger-for a while.

But you are flying an aircraft yourself now on the lateral channel. You are fighting transitions across the breakout force point and experiencing reversing stick forces. It is sort of like a cruel instructor trying to make your life very difficult by riding the controls and applying spurious inputs. It is impossible to fly the aircraft smoothly with this type of control interference. The best you can do is get a firm grip on the stick and balance your own muscles against each other so that the interfering forces are small in comparison to your own applied forces.

Problem. How do you keep from making inadvertent pitch inputs in this situation. Answer, you probably can't until you can release your grip on the stick back to more conventional levels.

"Oh that is easy", say you. Just move the rudder trim in the right direction and the plane will straighten up and fly right.
Problem. The PF has a serious roll control problem and a host of other distractions. He doesn't have the free brain cells to realize that his wing problem is correctable by the rudder, a different control surface. That takes a moment of calm insight which was not available. Remember, he's an Airbus guy. He flies with his feet on the floor to keep from accidentally kicking the tail around. His aircraft normally keeps everything in trim for him. He has never experience anything like this, particularly not at night, with a major pin ball show going on in front of him, at 2 in the morning.

Look at the BEA initial data report.
The initial roll was to the right. (There is your heavy wing.) And the PF made a left nose up control input. I wouldn't be surprised if his thumb was pointed up along the stick He probably was curling his wrist to control the wings. Mama Airbus is keeping the nose more or less where it belongs for now so I'm going to concentrate on getting these wings under control for now. If this thing rolls over, we are going to be doing a split S! Can't let that happen.

I wouldn't be at all surprised that we find that the majority of his control inputs were to the left and that he was accidentally pulling the nose up at the same time.
I'll bet that they find dents in the floor beneath the R seat rudder pedals, in a location indicating that his feet were still on the floor at impact.

Remember-whichever guy was PF, he was in the right seat and was therefore flying with his right hand The limited data made available seems to show that the rudder trim was never set. Whenever there is a description of the aircraft's roll behavior, it is oscillating.
Of course, once you get into a stall range, wing rock is a common result.

OK, I still have some work to do. Have a chew on this. There is more later if necessary.

Suggested area for discussion is, "What was the PNF doing all this while?"

[beachbunny]

Things like why the IAS for stall increases with altitude. Never found the answer to that anywhere else. ????

Come on guys, back to basics.

Thats because the airspeed does increase. Less density means less lift, so more speed is required to produce the same amount of lift.

[Capn Bloggs]

Thats because the airspeed does increase. Less density means less lift, so more speed is required to produce the same amount of lift.

That'd be the TAS that increases, BB.

[mm43]

Machinbird
He doesn't have the free brain cells to realize that his wing problem is correctable by the rudder, a different control surface.Good post. I've got an impression that there will have been a very disturbed airflow over the rudder, and with the AoA and the existing RTLU limitations, the +/-7.9° available may not be effective. We certainly don't know if the rudder was used, but if it was, the BEA must have seen nothing significant in its use, not to mention it.

[gums]

@Gray

We went thru this ( relaxed static stability and c.g. and....), and even posted charts and graphs and testimonials. I had to back off of some thoughts once some of the 'bus manuals were placed here for consideration. The 'bus is not nearly so "twitchy" as the jet I flew due to the c.g., and the company's goal of reducing drag due to down force by the rear stabs in cruise flight seems O.K. as long as you are FBW versus conventional flight control systems. I only brought up a discussion of the concept due to my own experience with "relaxed static stability" and the potential to reach a flight condition that is difficult to deal with.

There are several things about the 'bus flight control law implementation I do not like, but the basic concepts of the jet seem fair.

and for the 'bird observations:

- It is true that we tend to put in aft or forward stick when rolling right or left. Seems that some FBW systems with the small "side stick" are even canted to account for this. OTOH, I don't see this as a big deal for this accident.

- As 'bird has noted, rudder trim is available, but I can't find a note in the manual about the system "trimming" the rudder for zero yaw in the stable flight condition - no aileron input or pitch input, just flying st and level. With the laws that the jet uses, about the only thing I can see the rudder pedals for is nosewheel steering or countering roll when in a stall or close to a stall. This is due to basic swept wing aero.

- There is no roll trim on the beast, best I can determine reading all the manuals. This is unlike the FBW jet I flew, where roll command was identical in concept to the 'bus, but we carried ordnance and could have asymmetric loads that were a significant part of our gross weight. Our roll rate command was a bit more in magnitude, think max was about 280 deg per second at 16 or 17 pounds of pressure. Our trim max command was less than 280 deg/sec, hence, when my LEF folded up I had to hold constant pressure for about 15 minutes until getting back on the ground. Also had to trim rudder a bit.

- The pitch trim mechanization on the 'bus is gonna be a player in the final findings, and I'll place my bet now.

Why is that, Gums?

It's because you can't manually trim for a desired gee or attitude or AoA , even using the THS manual wheel. If you constantly hold even a slight bit of back pressure, the THS moves to help maintain your existing gee command and the elevators do the "fine" work. Need a 'bus driver to try this out in flight - jez kidding! Let go of the stick in Normal or Alt and the sucker re-trims the THS for a 1 gee baseline ( corrected for pitch attitude and bank angle, both to specified limits).

So my feeling is the constant back stick moved the THS to almost max, then got stuck there in Abnormal mode or was maintained there in Alt mode due to constant back stick gee command. No AoA limiter as we had in the Viper. In that sucker we hit 9 gees at 15 deg AoA and then if we continued to demand max pitch the gee command would be reduced to 1 gee at 25 deg AoA, even if we pulled 100 pounds on the stick. Our AoA limiter worked very well except at a combination of extremely high pitch attitudes and very slow speeds and little or no roll rate.

Gear down we added an increased AoA bias to the basic gee command, plus we increased pitch rate feedback. The result was a fair simulation of "normal" jet approach characteristics, in that we could trim for an airspeed/AoA versus a pure gee.

Finally, the THS can't help but be the primary driver at the edges of the envelope, and the elevators act like "trim tabs". It acts like the "all-moving" stabilizers you see on all the jet fighters.

[Machinbird]

- It is true that we tend to put in aft or forward stick when rolling right or left. Seems that some FBW systems with the small "side stick" are even canted to account for this. OTOH, I don't see this as a big deal for this accident.Hey Gums,
When your Leading Edge Flap (LEF) on your Viper folded up and you were flying with nearly full lateral stick, did that give you control problems other than banging into the control stop on one side?

I don't imagine you ever needed to go through the center of the lateral stick travel then. Would that have made life more interesting with the force reversals on the stick? (Never mind, your Viper stick didn't move, did it?)

Supposing your aircraft wasn't computer stabilized in roll any more and was oscillating quite a bit in roll. How much pucker factor would that have added?

Just trying to put Viper experience in a comparable context.:ugh:

[HazelNuts39]

So...as per comments above and your experience, can the difference between Mach buffet, and stall buffet, be felt/determined? Your thoughts...would one know when one is in high speed or low speed buffet? As explained in the previous thread, I don't think there is significant difference between high speed or low speed Mach buffet. Perhaps the frequency changes gradually with Mach number, and that may be noticeable if there is a large spread between the high and the low limit. But since an airline pilot never gets there, would he be able to recognize the difference?

[BOAC]

Suggested area for discussion is, "What was the PNF doing all this while?" - we both agree here - it really is less significant who was in which seat, since both pilots were line-qualified. What IS significant, as I have said a few times (it really is crucial and we are not being told!) is what PNF said during this amazing and frightening zoom climb. Until we know that we cannot progress, I feel.

How many of us would sit 'quietly' in this scenario? Was it a mutually agreed manoeuvre? If not, were 'challenges' issued? If it was agreed, why? There, surely, will lie the clues as to what PF was 'seeing'? Any 'leaks'?

To pick up on those questioning the absence of a 'Stall' warning at low IAS - I'm pretty sure that had this been not blocked, there would be a fair chance that they might have recovered and not sensed the need to 'reverse the last input' when it sounded again during recovery. It appears that because the designers were convinced this situation could not develop due to the 'protections' that they didn't bother?

[Right Way Up]

With regard to who sits in which seat it has been mentioned that the senior f/o must sit in the Lhs. In my previous company this was not the case. The acting pilot in command had to be in their trained seat. A rated pilot could sit in any seat in the cruise as long they or the other pilot was an APIC. We also were qualified for acting pilot in command if we had an ATPL and had completed our first recurrent check. Now I do not know what AFs rules are but the setup they used is not unusual and would suggest that the less experienced pilot was in the RHS and was in command.

With regard to the stall warning this troubles me that an integral part of dealing with unreliable airspeed is not actually always available. Surely this needs to have ground air logic as part of it's operating envelope.

[rudderrudderrat]

Hi Right Way Up,

With regard to the stall warning this troubles me that an integral part of dealing with unreliable airspeed is not actually always available. Surely this needs to have ground air logic as part of it's operating envelope.

I agree.

Also one wouldn't confuse the stall warning vibrations felt through the control column of a conventional aircraft with anything else. Under stressful conditions, crew can miss interpret audio clues easily (like the synthetic voice intermittently saying "stall stall" or "speed speed").

[RealQuax]

...just some observations out of 'daily life':

@ mach-buffeting: Experiencing Mach buffeting is common in normal operations: even within the normal speed envelope some transient speed-overshoots happen and buffeting is felt, although I didn't voluntarily fly into overspeed and don't know if it becomes much more prominent if doing so. I even think buffeting is (very slightly) noticeable once your speed goes beyond 0.84, which is well within the envelope....

@ stall-warning: Part of the last recurrent training was an unreliable speed-exercise (actually embedded in a 'flight into volcanic ash'-scenario including dual engine-failure, electrical emergency etc:) dunno how realistic the scenario/the simulation is: what really, really bothered both of us was the stall-warning which was not possible to be cancelled, although we definitely haven't been in a stall (thinking about it, it might be a deficiency of the simulator, since if it was AOA-induced, it could not have been valid, as there was no speed on the speed-scale, it should have been rendered invalid by the system): what I wanted to say is, that the permanent yelling of 'STALL, STALL' was so distracting that it almost made us agressive... not good if you have to think 'out of the box' and take decisions in ambigous environments...

@ PNF observing PF-stick-inputs: You do have to focus your view to PF's sidestick if you want to determine what he is doing. Given a scenario (Airbus SOP!) where the PF cares about flightpath and R/T and PNF cares about systems according to ECAM or QRH (and in this situation the main workload lies with the PNF!) there is not much monitoring-capacity left....
It's those situations where I miss the flight engineer most: A guy with intimate insight regarding the systems and some distance to the actual 'haptic' flying: BTW: both prominent examples about rescued airliners where pilots had to 'invent' flying to different rules than trained (Sioux City DC-10 and Baghdad A300) had a flight engineer, but that be only an outdated rant...
In so far, the situational overview of the captain once in the cockpit observing the both F/O's from behind might even be helpful solving such a situation...

[henra]

It is unlikely that a recovery could have been made without manually trimming the THS. At high alpha the elevator is not very powerful compared with the stabilizer. That this was not done suggests that the crew were not aware of the -13 degree THS setting. Doesn't it seem unlikely that if they were aware of it, and had identified the stall, they would have been deterred from using it by their simulator training? They were about to die. Or did I overlook something in the report?

Even if it gets tiring:
Could you point me to any indication the Crew identified that they were in a stall and that it was the THS trim that defeated their vigorous Nose Down command on the elevator ???

Furthermore:
Could you point me to a source that the THS wouldn't have returned to a more neutral / Nose down setting after continuous Nose Down would have dropped the Nose below 30° AoA ?

Until 10kFt I do not see any indication that the Flight condtion was properly identified by the Crew and any corresponding Text Book Recovery attemptes were made / sustained. That makes philosophying technical limitations to recovery obsolete, IMHO.
Below 10kFt recovering from a 40° AoA would have been impossible anyway.

Regarding the usefulness of an AoA indication:
It is definitely not clear if that would have made a change. It would have bbeen an additional opportunity though. But only if it is covered in the training as well. Otherwise it will be meaningless.
Indication of the Angle of the THS: I doubt it would have helped. I cannot see a Crew already overwhelmed by Information/warnings/alerts/chimes starting to look for even more data and rather 'irrelevant' ones from their perspective for that matter.

[FE Hoppy]

As explained in the previous thread, I don't think there is significant difference between high speed or low speed Mach buffet. Perhaps the frequency changes gradually with Mach number, and that may be noticeable if there is a large spread between the high and the low limit. But since an airline pilot never gets there, would he be able to recognize the difference?

Having experienced both as FE on test/acceptance flights on the Nimrod and L1011 I can say from my experience the buffet itself wasn't much different and had we not been aware of which regime we were entering I'm sure we wouldn't have been able to tell from the buffet alone.

I imagine that AF447, by the time it was at 380 with TOGA and 16° alpha was getting a bit of both!

[HazelNuts39]

what really, really bothered both of us was the stall-warning which was not possible to be cancelled, although we definitely haven't been in a stall (thinking about it, it might be a deficiency of the simulator, since if it was AOA-induced, it could not have been valid, as there was no speed on the speed-scale, it should have been rendered invalid by the system): what I wanted to say is, that the permanent yelling of 'STALL, STALL' was so distracting that it almost made us agressive... I'm amazed. What prevented you from doing the appropriate thing and drop the nose half a degree or so?

A propos stall warning. In Interim Report #2 BEA explains that stall warning starts when the AoA exceeds approx. 10 degrees at M=0.3, and at approx. 4 degrees at M=0.8. The update now provides a third datapoint of 6 degrees at M=0,633 (extrapolated backwards from 185 kt 15 seconds later). These points relate to alphamax as shown in this graph (https://docs.google.com/leaf?id=0B0CqniOzW0rjOWY3YmIyYjEtOWFhNi00YTEzLWJiNTItOGYyOTU wZTU4MDQz&hl=en_GB&authkey=CILGt_QN).

[deSitter]

BOAC above presented a report from Der Spiegel that a certain Prof. Huettig had re-created the incident in the simulator - the THS went up and stayed there - curtains. This seems to me to be the smoking gun in this crash.

Air France*Catastrophe: Victims' Families Propose Grounding All*A330s - SPIEGEL ONLINE - News - International (http://www.spiegel.de/international/world/0,1518,766148,00.html)

[Yankee Whisky]

QUOTE: deSitter
BOAC above presented a report from Der Spiegel that a certain Prof. Huettig had re-created the incident in the simulator - the THS went up and stayed there - curtains. This seems to me to be the smoking gun in this crash.

Air France*Catastrophe: Victims' Families Propose Grounding All*A330s - SPIEGEL ONLINE - News - International (http://www.spiegel.de/international/world/0,1518,766148,00.html)

-drl

In a previous posting I mentioned the AirCanada DC8 run away stabilizer trim causing an impossible force required by the pilots to pull effective up elevator even with their feet against the panel! This accident ended up with a big hole in the ground near the town of St Therese in Quebec, Canada.
Why should the AB 330 be any different and why would AB disqualify the
good professor Huettig's findings? There are just too many questionable things going on and we cannot rule out the industrial lobby's forces trying to influence the findings. :ugh:

[wes_wall]

Might as well give up the lack of info comments - quite obvious no more info will be forthcoming for a while - unless we get lucky and have a credible leak published.

I concur with Machinbird's possible scenario re the cause of the zoom climb. Full understandable and likely.

[Graybeard]

Does anybody understand the rationale for two sets of control laws between Normal and Direct? It seems to make systems management take precedence over aviating.

[robertbartsch]

Didn't the BEA permit AB to make a statement that they believe nothing needs to be modified in the A330 after the black box data was reviewed?

If that is true, BEA must believe it was a pilot only problem; right?

[Lonewolf_50]

Clandestino: your gracious response much appreciated. It occurs to me that if you've been a captain, you've been teaching pilots how to fly for quite some time. :cool: Apologies if my tone was anything other than cordial.
Can anyone confirm that "l'enregistreur de parametres" as fitted to AF 330s really doesn't record ADIRU2 (or ADIRU3) IAS output?

What display are you talking about?

Good question, I should clarify.
What I was referring to (what was in my mind as I posted that) was basic flying instruments: attitude indicator (pitch and roll aka AI), airspeed/Mach, altitude, vertical speed, slip and turn (which is incorporated into the AI if I read that diagram correctly), FPV.
-His Nav display may or may not have occupied his attention.
-Engine instruments in the center display position (to his left) probably dropped out early into the event. (ISIS seems a bit far across the cockpit for his scan unless he is sure AI is not reliable).
-Other warning displays on more than one display. How did they integrate into or disrupt his scan? Unknown. (Back to the "What was PNF doing?" consideration ... )
... left and ISIS pitot unclogged at different times so there's no reason to think that right pitot was in sync with either of the two remaining.
Agreed, which is why it would be interesting to know if what he saw was what ISIS and PNF saw, in re basic flight indications I note above. (EFIS, OK, better collective descriptor than my crude depiction) matched.
However there is no mention so far that any of the four attitude references tumbled or that ALT or VSI data got invalid at any time.

Roger, unknown, and important to keep bringing up, given the number of times we have seen (including some of my own "what if the gyro tumbled?" digressions in the last threads) statements that AI was not reliable. Not valid based on what has been released so far. Don't jump to any conclusion from that however. It will take much more than this "report" to have good idea what happened with AF447.

Indeed.

Again, thanks for the response. :)

[gonebutnotforgotten]

From HN39: A propos stall warning. In Interim Report #2 BEA explains that stall warning starts when the AoA exceeds approx. 10 degrees at M=0.3, and at approx. 4 degrees at M=0.8. The update now provides a third datapoint of 6 degrees at M=0,633 (extrapolated backwards from 185 kt 15 seconds later). These points relate to alphamax as shown in this graph.



That shows neatly how Stall Warning incidence is a function of Mach Number, so when the ADRs went belly up, what happened to the M input to the stall warning system, and what did the latter think the corresponding warning incidence (AOA) should be? Does it use the last valid IAS/M value as the rudder limiter system does?

Secondly the BEA states that right at the start of the sequence :From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row.

Does anyone know why the warning sounded at this stage? It's not obvious. Could it have been an indication of moderate or worse turbulence, because, after all, this was before the dramatic and inexplicable zoom climb, and before the sustained nose up side stick inputs that caused the THS to reach 13 deg airplane nose up? The aircraft should have been in a normal cruise condition at this earlier stage. Among lots of things the BEA hasn't chosen to reveal yet, is the general level of turbulence experienced before and during the upset. For that matter they haven't said whether there were any stall warnings before it all went wrong.

Note that in the Air Caraibes blocked pitot event they also reported a 10 second stall warning about 30 secs after the AP disconnect and start of the general brouhaha. The crew decided this was false, in accordance with advice in the <<ADR CHECK PROC>>, though the ACA report notes that elsewhere the crew are told to ignore that advice and respect the stall warnings. Confused? Those issues don't seem to have been resolved, at least not in readily available documents or posts here.

[bearfoil]

@Graybeard

"Does anybody understand the rationale for two sets of control laws between Normal and Direct? It seems to make systems management take precedence over aviating."

GB

That basic question lit the original thread on fire for pages, and from the git go.

Firstly, I believe there are three control domains twixt N and D, if one counts Abnormal (ironic?). Just as Piloting is changing its format to reliance on automation, what gets left behind is what has become most important, Know the Airplane.

There is no challenge to the gestating supremacy of Auto Flight in allowing, (Training) airmen and women to know the personality of their a/c backwards and forwards. What is the insult to parochial aero programming inherent in aviating skills? Such Hubris. "It did exactly what it was supposed to".

I beg to differ, for if any of the doubts expressed here are proven, what remains is "I'll do this, and if it 'doesn't work', it's on you". Always the defensive, and dismissive attitude. Arrogance has always been deadly in aviation.

The lack of a fossil AH on the panel was a shorter discussion, as many were astonished to find that so 'common' an occurrence as 'Unreliable Airspeed' could (did) leave both pilots without attitude, or 'assiette' data, (display).

@gbnf

"From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row."

This is reliant on the undivulged time line, for BEA state only "From....."
Anyways, after the 2:10:05 id. "Twice in a row" means to me, two short alarms, and my guess is that these were related to AoA rate transients, not a Stall per se. "chirp, chirp."

The Plane rolling right meant that a/p had been trimming out a chronic and trending condition, both Right wing heavy, and NOSE HEAVY. The THS was at 3 degrees when a/p dropped, what was the nature of the dropping Nose? Was it dropping continually, and continued to drop after a/p drop? Yes, because the THS was running behind its trim command from FMC, by definition. Nose and right wing dropping, a condition identified by both the a/p and the handed-to PF. This is suggestive not of Turbulence, but controls damage, weight issues (cg), Fuel scatter, etc. or ICE. Even an inop or over limited Rudder. Perhaps?

[Lonewolf_50]

gonebutnotforgotten:
That shows neatly how Stall Warning incidence is a function of Mach Number, so when the ADRs went belly up, what happened to the M input to the stall warning system, and what did the latter think the corresponding warning incidence (AOA) should be? Does it use the last valid IAS/M value as the rudder limiter system does?
I looked at HN39's graph.

What you say in re stall as "a function of Mach number" seems to me "correlates to Mach number," since the stall approach, condition of stall, and warnings, (unless I misunderstand the system) are triggered by a signal from the AoA sensing system.

AoA sensing subsystem is independent of the Airspeed/Mach sensing sub system. The computer receives signals from both and uses various logic to reconcile them, which seems to be your further point, and a potential point of failure or ambiguity. (The clipping of AoA info below 60 kts has been discussed, pro and con, at some length in the Rumors Forum thread ...)

If I misunderstood your point, apologies.

bearfoil:
The lack of a fossil AH on the panel was a shorter discussion, as many were astonished to find that so 'common' an occurrence as 'Unreliable Airspeed' could (did) leave both pilots without attitude, or 'assiette' data, (display).
bear, what do you mean by a fossil Artificial Horizon? The ISIS back up display has a back up AH. As yet, no evidence that the AH's embodied in the glass cockpit displays (for basic flying instruments I note above to Clandestino) were other than functioning per spec.

I are confused at your point there. :confused:

[bearfoil]

LW

I'm writing with some very old notes, I may traipse back a couple years, the notes are not mine, apologies. My understanding is the pilots were without any reliable instrumentation re: AoA. If one is committed to, and experiencing stable cruise flight, attitude is critical when things go bump? Pitch is in there?

a33zab

Abnormal? I count three Law hurdles between Normal and Direct. Also the a/c can go direct/Direct with pilot input, yes? Touch the wheel, bypass A1,A2, and Ab. No one will get fired without offers of employment elsewhere, I think.

[circuitbreaker13]

I don't fully understand the discussion over the HST because (I will put it as a question) would it not have followed to a nose down posn if the PF would have gave nose down on the stick and therefore have overcome this situation?

[bearfoil]

I think Flight Law at the time of Stall/descent was not auto trim, and would have required manual input on the two wheels bracketing the Throttle pedestal?

(See MartinM's great pic)

[sensor_validation]

I know its been discussed before - and was one theory proposed by BBC/Nova - but would the speed change from M0.82 to M0.80 have been complete before the UAS? If pitot drains simultaneously block first the IAS over-reads, then if total pressure ram port blocked speed is locked in - UAS may only be detected when drain holes asymmetrically unfreeze. If this happens while in transition true air speed could have undershot target - and A/P pitch up to hold altitude? So out of trim when A/P A/T disconnect requiring immediiate manual correction?

[bearfoil]

The Plane rolling right meant that a/p had been trimming out a chronic and trending condition, both Right wing heavy, and NOSE HEAVY. The THS was at 3 degrees when a/p dropped, what was the nature of the dropping Nose? Was it dropping continually, and continued to drop after a/p drop? Yes, because the THS was running behind its trim command from FMC, by definition. Nose and right wing dropping, a condition identified by both the a/p and the handed-to PF. This is suggestive not of Turbulence, but controls damage, weight issues (cg), Fuel scatter, etc. or ICE. Even an inop or over limited Rudder. Perhaps?

[lomapaseo]

BOAC above presented a report from Der Spiegel that a certain Prof. Huettig had re-created the incident in the simulator - the THS went up and stayed there - curtains. This seems to me to be the smoking gun in this crash.



I take these kind of breaking news reports with a grain of salt.

I have played arround with some manufacurer's simulators trying to recreate scenarios and some interesting things happened. After some anaysis of the surprise it was mostly the limitation or programmng of the simulator that was causing the reaction. So ... I'm not ready to accept the reported facts in the Der Spiegel report as useful until the BEA completes their analysis.

Page after page of this discussion convinces me that somewhere one of you is going to be lucky and guess at some smoking gun contributor but until the total picture is put in perspective by the BEA I'm not about to scream for a corrective definied action.

Meanwhile carry on with helping us understand how the thing is supposed to work

[rudderrudderrat]

Hi bearfoil

The Plane rolling right meant that a/p had been trimming out a chronic and trending condition,

Alternate Law.
"LATERAL CONTROL

When the aircraft flying in pitch alternate law, lateral control follows the roll direct law associated with yaw alternate or mechanical."

So a bit of Left Rudder would have levelled the wings.

[Lonewolf_50]

LW

I'm writing with some very old notes, I may traipse back a couple years, the notes are not mine, apologies. My understanding is the pilots were without any reliable instrumentation re: AoA. If one is committed to, and experiencing stable cruise flight, attitude is critical when things go bump? Pitch is in there?
Bear, I am questioning what seems to be your substituting attitude instrumentation (artificial horizon) for AoA instrumentation (Angle of Attack indication). Apologies if you already understand what follows.

If I fly with my nose at (for example) 2 degrees below the horizon, and vary the airspeed, AoA will vary. If I keep my airspeed and attitudes within the normal operational range, my AoA stays comfortably away from critical, and I don't stall.

To say the pilots did not have attitude indication (artificial horizon) is not correct. Three displays of the aircraft's attitude are in the cockpit. One is in front of each pilot, and one back up in the ISIS instrument cluster.

That most airliners apparently don't have separate AoA gages does not stop pilots flying day to day airline routes from having an attitude reference: attitude (artificial horizon) is the primary reference instrument in instrument flying.

While AoA is related to attitude ... and AoB ... and airspeed ... and power ... and g load ... and air density ... etecetera), it is not correct to derive from that an AoA gage being the equivalent of an artificial horizon, which is an aircraft attitude (pitch and roll) instrument.

[A33Zab]

Bearfoil:


Abnormal? I count three Law hurdles between Normal and Direct


Abnormal law is a sub-law available in alternate 1 or 2 when e.g. alpha exceeds +30 or -10 or any other predetermined limitation exceedance.

Abnormal law:
- in roll: the yaw alternate law.
- in pitch: an adapted Nz law, without autotrim.
After A/C recovery, and until landing, the available laws become:
- in roll: the yaw alternate law.
- in pitch: the Nz law, with recoverd autotrim.

Touch the trimwheel -AND- and after A/C recovery it will stay in abnormal law with auto pitch trim.

See previous post: http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-48.html#post6486875

Manual Pitch trim movement will not initiate a law-change and has always priority!

[t54]

"From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row."

...and because of this the PF followed standard (low altitude) stall procedure, setting power to full and raising the nose somewhat?

There is no timeline quoted her. The Stall warning might have been the first indication that the PF had that something was amiss.

[bearfoil]

Lonewolf50

Yes, I get. In Unreliable a/s, the a/c is in Alternate Law, out of autopilot and autothrottle. So some (ill-defined?) combination of Manual and residual control is necessary. To maintain cruise, (that's the idea?), until A/S is recaptured and auto pilot can be reselected, the idea is Pitch and Power. At the beginning of the thread, my assumption is, well, Pitch and Power, then. Some combination of NU and %N1, yes? Table, PNF, memory, Bob's yer oncle?

I may have missed a key piece of info in the plethora of posting around maintaining aero flight. I may need to re-assess; Did our boys have access to means of pulling the fat back from the fire, and screwed the Poodle?

Within the realm of cruise in a commercial airliner, and a knife fight with duelling Vipers or Phantoms, AoA? Am I wrong in taking for granted that in Commercial flight at the "edge", Pitch and N1 are insufficient to keep the flight safe?

If Pitch and Power are the fallback, de jure, someone needs to teach the Airbus pilot to fly AoA? Okay, Fine?

bear

t54

"From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row."

This is reliant on the undivulged time line, for BEA state only "From....."
Anyways, after the 2:10:05 id. "Twice in a row" means to me, two short alarms, and my guess is that these were related to AoA rate transients, not a Stall per se. "chirp, chirp." In any case, the Stall warning happened at the same time (between a/p drop, and PF's left,NU input). This is in legal jargon, exculpatory.

"...and because of this the PF followed standard (low altitude) stall procedure, setting power to full and raising the nose somewhat?"

Not "raising the nose" in recovery from approach to Stall, but "Maintaining Altitude", two very different things. Since the Nose was dropping at handover, PF's flying was by the book, no matter the Training Syllabus.

Airbus instituted its "MODIFICATION OF STALL RECOVERY" AFTER 447 went in.

LW

"Put another way, if your aircraft stalls at 6, or 8, or 10 or 12 units/degrees AoA, and you are at 30, you are well behind the aircraft. A design assumption seems to be "if you get this far into stall, the computer may be a problem contributing to the situation, get it out of there so you can get this bird out of a stall!" "

So some means of "get" and control movement needs some tweaking, eh?

I may be letting some AB philosophy in, finally. "That does not absolve the airframe builder of responsibility here. Selling someone some hardware and not training it exhaustively is a chasm of Arrogance."

This will no doubt be at least one of Plaintiff's claims (theories).

[Lonewolf_50]

Abnormal law:
- in roll: the yaw alternate law.
- in pitch: an adapted Nz law, without autotrim.
After A/C recovery, and until landing, the available laws become:
- in roll: the yaw alternate law.
- in pitch: the Nz law, with recoverd autotrim.
This bolded part is where a stalled aircraft could require trim wheel input to help move the THS to a position where it helps recover from the stall, since if that law kicks in your sidestick/elevators may not get the THS moving. (Based on the control authority points made previously regarding elevators and THS)

If one does not practice stalling that far
(some would call that bleeding practice, since the idea of stall recovery is typically "unstall as soon as you can, don't wait for it to get worse")
one might not recall that change -- using a secondary flight control, a trim wheel -- when one is playing catch up to the aircraft.

Put another way, if your aircraft stalls at 6, or 8, or 10 or 12 units/degrees AoA, and you are at 30, you are well behind the aircraft. A design assumption seems to be "if you get this far into stall, the computer may be a problem contributing to the situation, get it out of there so you can get this bird out of a stall!"

The more I think of how that law is set up, the more it makes sense.

If you are an unusual attitude, you don't want the computer interfering with your attempts to fly out of it. This law means that the aircraft not only allows you to fly (pitch, anyway) manually without computer interference, but requires you to fly manually without computer assistance.

But if you don't train to do it ... will you remember to fly it that way when you need it? :confused:

[OK465]

what really, really bothered both of us was the stall-warning which was not possible to be cancelled

what I wanted to say is, that the permanent yelling of 'STALL, STALL' was so distracting that it almost made us agressive... not good if you have to think 'out of the box' and take decisions in ambigous environments...


Academic point only (assuming you're talking A330):

If you could not cancel the stall warning with the EMER CANC button in your sim, you may want to get your simulator checked/fixed. Unless it varies by model, I believe only gear related warnings & ground prox stuff can’t be cancelled with EMER CANC. However even these continuous audio warnings can be temporarily cancelled by holding down EMER CANC. They will resume when it is released.

It’s interesting that no one has commented on the fact that the initial stall warning termination (though assumed due to unreliable data) also coincided with the Captain’s arrival and attempt to provide verbal info. If I were up front I might instinctively hit the EMER CANC so I could fully hear what he was saying. (Maybe someone has brought this up and I missed it here in the 3 volumes of “War & Peace”.)

[BOAC]

The problem with the AB system appears to be that no-one actually understands it so heaven help pilots caught in a software maze! Each AB 'expert' comes here and we get different shades of the event. Even Flight Global appears confused:

The abnormal attitude law is a subset of alternate law on the aircraft andis triggered when the angle of attack exceeds 30° or when certain other inertial parameters - pitch and roll - become greater than threshold levels.
Alternate law allowed AF447's horizontal stabiliser to trim automatically 13° nose-up as the aircraft initially climbed above its assigned cruising altitude of 35,000ft.
The stabiliser remained in this nose-up trim position for the remainder of the flight, meaning that the aircraft would have had a tendency to pitch up under high engine thrust.
Crucially the abnormal attitude law - if adopted - would have inhibited the auto-trim function, requiring the crew to re-trim the aircraft manually.
After stalling, the A330's angle of attack stayed above 35°. But while this exceeded the threshold for the abnormal attitude law, the flight control computers had already rejected all three air data reference units and all air data parameters owing to discrepancy in the airspeed measurements.
Abnormal law could only have been triggered by an inertial upset, such as a 50° pitch-up or bank angle of more than 125°. "That never occurred," says French accident investigation agency Bureau d'Enquetes et d'Analyses."

Can anyone give me a clear, unambiguous explanation of why 'Abnorml Law' did not engage and how the two underlined bold bits go together??

[bearfoil]

For one thing, as a "subset", ABNORMAL LAW IS technically "ALTERNATE LAW", and until one sees the actual data, perhaps BEA is parsing the Camel? So let's be broad minded, give the benefit of the doubt to BEA and entertain that the a/c went DIRECTLY into Abnormal Law.

For discussion only, the slim pickens are well short of any definitive answers, by design, I would say. Not even bear is pushing a theory at this point.

"Calling for conclusions not based on facts in evidence". .....Perry Mason 101.


"Any change in available controls, operation, limits, or results shall constitute a LAW change." Don't change the rules and call it something it ain't.

[t54]

bearfoil
"Not "raising the nose" in recovery from approach to Stall, but "Maintaining Altitude", two very different things."

Point taken.

I read somewhere that the initial two stall warnings were a valid response to the invalid 60kt pitot reading. Maybe the stall warning comes first in the relevant part of the computer program , before the validation of the data upon which the stall warning is based.?
Anyway, could the assumption by the PF that the initial short stall warnings were valid explain the climb?

[PuraVidaTransport]

In the Flight Global article, they are making the distinction that the aircraft never went into the abnormal attitude law because the flight computer had rejected the information coming in from the ADRs before those parameters were met. The aircraft was already in alternate law from the loss of airspeed. The last underlined part is saying that the flight computers would have to see 'acceptable' data from the ADRs to trigger this law like the examples given.

[Lonewolf_50]

For BOAC: we both seem to have seen something amiss in two different threads, and that article, from a different entering point.
I share your question. Does it or doesn't it (in re AoA at 30?) :confused:

For Bear:

The idea of teaching Air France pilots to fly AoA would require an AoA gage in the cockpit (not likely any time soon) and probably isn't as important a training issue for Air France as:

"How do we confirm basic fly pitch and power handling, and basic instrument flying skills, are up to the standards we expect and assume?"

The answer to that ain't trivial. What if the average AF pilot is a perfectly good, or even above average, instrument pilot. What if the line pilots are found to be good to very good through a sampling that shows skills and knowledge up to standards.

Then what do you do? What if that particular person/event match up was anomalous? Would you tamper with a system (back to Deming's caution against that) when most of your data show it operating well?

This is where the pilots in Air France doubtless have a crucial role, and ought to be listened to carefully, in any attempt to change something.

For OK:

It’s interesting that no one has commented on the fact that the initial stall warning termination (though assumed due to unreliable data) also coincided with the Captain’s arrival and attempt to provide verbal info. If I were up front I might instinctively hit the EMER CANC so I could fully hear what he was saying. (Maybe someone has brought this up and I missed it here in the 3 volumes of “War & Peace”.)
Sounds like a PNF action.

[Welsh Wingman]

I have been reading PPrune posts for many years (always appreciate from afar what PJ2 has to say) before finally feeling compelled to register and throw in my thruppence worth (for what it is worth, having long since retired from B747 classics, from my retirement cottage...).

This reminds me somewhat of the Erebus/TE901 crash back in 79, where an air crash investigator (used to small aircraft investigations) put all the blame on the DC-10 flight crew. It took Justice Mahon to look at the systemic failings at Air NZ, and point out that programming the plane and the pilots of a low flying sightseeing plane near to high ground to fly to different locations in Antarctica was unlikely to result in a happy ending (particularly last minute amendments to the flight plan co-ordinates without notifying the flight crew). There is seldom a single failure leading to a plane crash, but rather an entire chain of unfortunate events that could have been, but were not, interrupted at any stage....

BEA have got to be very careful about what they release, including from the CVR/FDR, and will dare not release anything at this stage that they are not absolutely certain they can verify. To put it mildly, they don't want the lawyers of Air France and/or Airbus pulling anything they say/imply apart and we will have to be patient. I have confidence that BEA will get there, but they have huge domestic commercial sensitivities (albeit the last thing that they want is an international observer, e.g. from the AAIB, disavowing their final report) to factor in (rightly or wrongly) to avoid needlessly damaging on the road there and we must accept that.

The one thing that we can be certain about is that the BEA are, as we write to each other, going through all areas and particularly the interface between machine and pilots, and this will take time. There will be agonising/soul searching over Airbus design/philosophy issues and Airbus/Air France pilot SOPs - high altitude A/P and autothrust disengagement and the flight envelope/crew response implications, the lack of redundancy with the loss of air speed data (and why the Thales pitot tubes were not changed sooner, given this obvious redundancy issue and criticality to safe A/P operations), the PF's stick movements (backwards in particular) and the PNF's (& Captain's from FLT 350 down) ability to see these movements, that climb up to FLT 380 and the THS going to 13 for the duration of the alternate law flight, weather radar training and the possible weather deviation limitations for this plane on this particular route (unless the flight crew want to land in Bordeaux and endear themselves to flight ops...), why the pilots did not appear to recognise the high altitude stall at all (including no AoA indication or BUSS installation on this aircraft) when they had FLT 380 to get out of it (troubling to an old salt like me trained by the Fleet Air Arm in the early-60s to lower nose/increase power!) and the ability of flight crews to immediately correctly identify the problem and correctly respond if possible/permitted by the remaining systems (in the face of such an urgent problem, used to so much automation and never touching the manual trim wheel).

This all being said, keep up the good work and keep your thoughts/ideas coming. I bet somebody from the BEA will be taking a look at some of the more informed comments. Just be patient with the BEA. There will be a lot more, on the CVR in particular. For what it's worth, I don't expect and can't see (save for any "smoking gun" in relation to unexpected system performance outside of normal law) any party (Airbus/Air France/the flight crew) being totally "exonerated" on this one.......

[bearfoil]

I am weary of folks accepting counterintuitive and plain wrong assumptions, including me.

If the a/s was 60 knots, and the a/p was in, we need to talk. If the Stall warning was on, and the a/c was not in ABNORMAL LAW, likewise. Monsieur takata swears that a/p drop was UAS driven, in spite of a time line provided by BEA.

Screw ACARS, all right? Old habits, etc. If the a/p was in, and the PF had a Stalling a/c in his mitts, he had a correct response.

Cruise flight is not easy to parse into BITS, it is a dynamic Dance, and these guys had an "Unfolding" (Unwinding) Flight Path. May we start there? Back to read only.

[BOAC]

the initial two stall warnings were a valid response to the invalid 60kt pitot reading. - there you go - we are first told Stall warnings are AoA driven now we 'read' they are IAS driven.

Those first two certainly puzzle me, whatever triggers them..

[jcjeant]

Hi,

Sorry if I'm dumb .. but .. someone can make a technical comment (explanation) about the text in bold .. ?

From the 27 May BEA report:

Around fifteen seconds later, the speed displayed on the ISIS increased sharply towards 185 kt;
it was then consistent with the other recorded speed. The PF continued to make nose-up
inputs. The airplane’s altitude reached its maximum of about 38,000 ft, its pitch attitude and angle of attack being 16 degrees.

Thank's in advance.

[rudderrudderrat]

Hi jcjeant,

The only way I can imagine that is if they "bunted over the top" so the wing loading was much less than 1g.

[Lonewolf_50]

t54, I am confused again.
I read somewhere that the initial two stall warnings were a valid response to the invalid 60kt pitot reading.
Maybe the stall warning comes first in the relevant part of the computer program , before the validation of the data upon which the stall warning is based?

Stall warnings, and stall α, are shown in HazelNuts39's graph (https://docs.google.com/leaf?id=0B0CqniOzW0rjOWY3YmIyYjEtOWFhNi00YTEzLWJiNTItOGYyOTU wZTU4MDQz&hl=en_GB&authkey=CILGt_QN)
They are based on AoA, the magnitude of which is influenced by airspeed/mach number.

I don't understand how you reach the idea of a stall warning based on an invalid (or even a valid) airspeed reading, since stall warnings are (should be?) based upon AoA which is not the same as airspeed. It is a different parameter, influenced by airspeed, attitude, gross weight, angle of bank, G, air density ... etc

From earlier posts: what the 60 knots threshold seems to have triggered is a disabling of a stall warning, which is itself enabled by an AoA reading as shown in HazelNuts39's graph.

Does that make sense?
Anyway, could the assumption by the PF that the initial short stall warnings were valid explain the climb?
Do you mean due to an increase in power as a response to stall warning?

Not an Airbus driver, but my assumption on stall response is decrease AoA via attitude change, and increasing power with the intent of increasing speed and thus decreasing, for the same attitude, AoA further away from stall margin. (EDIT: if you don't recognize or know you are stalled, or believe you are not stalled, you might not make that response).

For bear:
Am I wrong in taking for granted that in Commercial flight at the "edge", Pitch and N1 are insufficient to keep the flight safe?
Based on PPRuNe posts regarding this crash, posts made by actual airline pilots who fly heavies at those altitudes, posts since about 02 June 2009, the answer to your question is that pitch and power are indeed, and should be, sufficient to maintain flight.

The estimates back then frequently led to "didn't know to fly pitch and power? If they didn't why didn't they?"

Info to date released by BEA seems to confirm that setting pitch and power for that altitude and desired performance isn't what happened ... but the why remains elusive at present.
If Pitch and Power are the fallback, de jure, someone needs to teach the Airbus pilot to fly AoA? Okay, Fine?
Not really. If pitch and power are the standard fall back, (and it appears that numerous pilots and airlines have procedures that are precisely just that for UAS conditions, and these work,) then "flying AoA" is a subsequent skill set suitable for other flying applications.

Referring to AoA as a crosscheck if Airspeed becomes unreliable has been suggested (to confirm "what is my wing doing?") as a suitable improvement to the pilot's tool kit. (A lesson learned, if you wish).

[DozyWannabe]

BOAC above presented a report from Der Spiegel that a certain Prof. Huettig had re-created the incident in the simulator - the THS went up and stayed there - curtains. This seems to me to be the smoking gun in this crash.

The simulator is not the aircraft - given that it seems that they were in a situation that had not even been encountered in test flying, so no data with which to program the simulator. There are no details as to the specific actions Prof. Huettig performed, or how they correlate to the actual actions as they were performed in the flight deck.

I find it quite ironic that you of all people, who considers software so unreliable and so many of the people who create software to be... What was it? I believe the word was "dolts" (no offence taken, sir...) would be willing to put his whole weight behind a "smoking gun" derived from a computer simulation that was based on incomplete data.

Does anybody understand the rationale for two sets of control laws between Normal and Direct? It seems to make systems management take precedence over aviating.

It's simple really - past the dry engineering language it boils down to the fact that Alt1 has protections, Alt 2 (effectively) does not. If I were a pilot, I would be very wary of relying on any of the remaining protections in Alt Law to back me up, doubly so in a situation when there's an obvious data capture issue (or in aviation terms, unreliable instrument readings).

As yet, no evidence that the AH's embodied in the glass cockpit displays (for basic flying instruments I note above to Clandestino) were other than functioning per spec.

Correct.

I'm writing with some very old notes, I may traipse back a couple years, the notes are not mine, apologies. My understanding is the pilots were without any reliable instrumentation re: AoA. If one is committed to, and experiencing stable cruise flight, attitude is critical when things go bump? Pitch is in there?

AoA information and functioning AH/AI/ADI (whichever you want to call it) are not one and the same thing, bear. On modern aircraft (talking about anything post 757/767), attitude information is provided from a redundant pair of electronic gyro boxes known as an AHRS. Attitude information does not rely on either AoA vanes or Pitot/Static sensors.

I refer you again to the Birgenair accident where the aircraft (a 757) was effectively in the same situation, though it was a case of the captain's blocked pitot tube being hooked up to the FMS (autopilot), thus inadvertently creating a single point of failure rather than all pitots being blocked. In fact by programming the FCU to detect multiple pitot failure and kick the autopilot out upon detection, Airbus actually created a safer design. The Birgenair 757's FMS actually tried to fly the aircraft on the bad information, pitching the aircraft up to an extreme AoA, and it was only that extreme AoA that caused the FMS to switch out. If I recall correctly (and please, anyone, correct me if I'm wrong) Boeing later retrofitted the 757 and 767 fleet to enable selection of pitot/static data to the FMS, so that a failure on one side would not be catastrophic.

In that case, the all the ADIs (powered by AHRS) were functioning perfectly, and the relief F/O repeatedly called out "ADI!" on the way down, pointing out that the aircraft was in an extreme nose-high attitude (the other F/O, who had a working ASI repeatedly called out that they were stalling) - all the way down to the ocean. The pilot in that case, as I've said before - no low-hour newbie, but an experienced ex-Air Force jockey appeared to be so overwhelmed that he failed to check the ADI in front of him that was telling him he was nose-high, even as his F/Os were emphatically telling him what to look at.

The Plane rolling right meant that a/p had been trimming out a chronic and trending condition, both Right wing heavy, and NOSE HEAVY. ... Perhaps?

Bear, you've got to be careful how you phrase this stuff. A newcomer to this thread would think that what you're presenting is a known fact rather than a theory posited by a single poster that is based on no evidence whatsoever.

BOAC, If the context wasn't so serious, I'd be willing to wager with you that what comes out of this will prove all this talk of software and laws to be something of a red herring. We've seen two 757s go down due to pitot/static failure and their controls were not software-driven.

That said, if what some posters are saying about inadequate training in use of the manual trim wheel is true, then it's a major problem, but it's not a software problem. Ultimately, even if you're in Normal Law and you don't like what the trim is doing you can grab that wheel and set it manually.

I know that the increased presence of computers in the flight deck is an emotive issue for pilots, but I can assure you that from the perspective of this software engineer, and, I'd be willing to wager even more - every software engineer who worked on the FBW aircraft that are flying today - we are on your side. We are trying to make your job easier. The systems we built were specified and designed from requirements put forward in the main by pilots. We are not intending to replace you. If your employers are saying that the technology effectively reduces you to systems monitors - and that hand-flying is discouraged - then they are abusing what we gave them, and as PJ2 says, you *must* fight them on it for the sake of every person who boards your aircraft. That was not the intent, and I hope never will be in my lifetime.

[t54]

BOAC
I got that "stall warning triggered by low air-speed indication from -
Initial Air France Flight 447 Black Box Info Raises More Questions Than Answers: Pilot | NYCAviation (http://nycaviation.com/2011/05/initial-air-france-flight-447-black-box-info-raises-more-questions-than-answers-pilot/)

I was a bit surprised because I had thought stall was purely a function of AOA, and no doubt air density as well. But I can see that air speed might come into it to, but I would have to have the mechanism of that explained to me

[MurphyWasRight]

LW50:
Referring to AoA as a crosscheck if Airspeed becomes unreliable has been suggested (to confirm "what is my wing doing?") as a suitable improvement to the pilot's tool kit. (A lesson learned, if you wish).


Before adding AoA crosscheck to the "pilots tool kit" it needs to be added to a display somewhere a pilot can access it.

Unless I misread something UAS blanks out the one "proxy" AoA display available to the pilots.

[Lonewolf_50]

Dozy:
In that case, all the ADIs (powered by AHRS) were functioning perfectly, and the relief F/O repeatedly called out "ADI!" on the way down, pointing out that the aircraft was in an extreme nose-high attitude (the other F/O, who had a working ASI repeatedly called out that they were stalling) - all the way down to the ocean.

The pilot in that case, as I've said before - no low-hour newbie, but an experienced ex-Air Force jockey appeared to be so overwhelmed that he failed to check the ADI in front of him that was telling him he was nose-high, even as his F/O's were emphatically telling him what to look at.
The human factors element of this mishap seems an apt parallel to what AF 447's PF might have been experiencing.

@Murphy:

Yes, of course, sorry I left that out. As I noted earlier, choosing what piece of "real estate" in the display area would house an AoA gage requires careful consideration, and some ergonomic and "scan efficiency" study before a decision is taken.

[CogSim]

Originally posted by tk54
I read somewhere that the initial two stall warnings were a valid response to the invalid 60kt pitot reading.
Maybe the stall warning comes first in the relevant part of the computer program , before the validation of the data upon which the stall warning is based?

Originally posted by Lonewolf_50

Stall warnings, and stall α, are shown in HazelNuts39's graph
They are based on AoA, the magnitude of which is influenced by airspeed/mach number.

I don't understand how you reach the idea of a stall warning based on an invalid (or even a valid) airspeed reading, since stall warnings are (should be?) based upon AoA which is not the same as airspeed. It is a different parameter, influenced by airspeed, attitude, gross weight, angle of bank, G, air density ... etc

From earlier posts: what the 60 knots threshold seems to have triggered is a disabling of a stall warning, which is itself enabled by an AoA reading as shown in HazelNuts39's graph.

From the report:

Note: 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. When they are below 30 kt, the speed values themselves are considered invalid.

The question is has the system rejected a/s (60 kt) by this point? If so, why is it still being honored by AoA logic?

"When they are below 30 kt, the speed values themselves are considered invalid."

Considered invalid by which sub-system? AoA logic? BEA doesn't say.

[oldchina]

"possible weather deviation limitations for this plane on this particular route (unless the flight crew want to land in Bordeaux and endear themselves to flight ops...)"

Weather deviations should cost peanuts in fuel quantity (ask your math teacher) so can we put this one to bed please...

[DozyWannabe]

The human factors element of this mishap seems an apt parallel to what AF 447's PF might have been experiencing.

LW_50 :

Many thanks. I've been saying this since the tail-end of the previous thread, when interest picked up over the BEA's "note", but very few people seem to have noticed. In addition, I was also clued in to the BEA's report on the Moscow A310 incident, which referred back to data that says that without proper training, 80% of pilots instinctively pull back on the yoke or stick when confronted with an unexpected stall warning.

[One Outsider]

I am weary of folks accepting counterintuitive and plain wrong assumptions, including me.

If the a/s was 60 knots, and the a/p was in, we need to talk. If the Stall warning was on, and the a/c was not in ABNORMAL LAW, likewise. Monsieur takata swears that a/p drop was UAS driven, in spite of a time line provided by BEA.

Screw ACARS, all right? Old habits, etc. If the a/p was in, and the PF had a Stalling a/c in his mitts, he had a correct response.

Cruise flight is not easy to parse into BITS, it is a dynamic Dance, and these guys had an "Unfolding" (Unwinding) Flight Path. May we start there? Back to read only.

What a load of twaddle!

This persistent habit of inventing stuff out of the blue, and presenting it as it is somehow fact, while ignoring or distorting what is known fact, to allude or insinuate that the aircraft suffers from some unspecified flaw and that the BEA is in cahoots with the establishment to somehow pin it on the crew is really getting old.

Give it a rest, for everybody's sake.

[bearfoil]

Doze

"Bear, you've got to be careful how you phrase this stuff. A newcomer to this thread would think that what you're presenting is a known fact rather than a theory posited by a single poster that is based on no evidence whatsoever."

There is no evidence as yet. Evidence is entered under penalty of perjury, and as "held and factual".

Here, we have ACARS, some few motes of "data", and miles of "O'Briennese" (no offense, mate). If a/p dropped, any flight vectors that had been under control, would have reverted to untrimmed, or been patent under a/p commands. Thus, "Trending". Not obvious? Fine.

Any one who is misled by reading any of this, needs a therapy. Informed opinion, at best. You give at least this old pilot too much credit.

happy day, Sir.
bear

ec, one outsider........


"This persistent habit of inventing stuff out of the blue, and presenting it as it is somehow fact, while ignoring or distorting what is known fact*, to allude or insinuate that the aircraft suffers from some unspecified flaw and that the BEA is in cahoots with the establishment to somehow pin it on the crew is really getting old."

*"known fact"........Sorry?

[t54]

jcgeant
"Sorry if I'm dumb .. but .. someone can make a technical comment (explanation)
about the text in bold .. ?

From the 27 May BEA report:
Quote: Around fifteen seconds later, the speed displayed on the ISIS increased sharply towards 185 kt;
it was then consistent with the other recorded speed. The PF continued to make nose-up inputs. The airplane’s altitude reached its maximum of about 38,000 ft, its pitch attitude and angle of attack being 16 degrees."

That is puzzling. If the wing chord angle is zero it makes sense - the plane was moving horizontally through still air. I can't see how it can ever happen if the chord angle is not zero with a horizontally moving plane (which is implied by "reached maximum altitude").

[DozyWannabe]

Bear, don't be obtuse. I meant evidence in general terms (as in a fact or collection of facts), not legal.

[EDIT : I note that you're flying your true colours more obviously on the sister thread in R&N:

Suggest a

"LAWS of TOULOUSE" become a sticky.

:ugh: ( Laws of "too loose"? )

]

[grity]

t54 its pitch attitude and angle of attack being 16 degreesits geometrie: in still air if the flightpath = chord angle (mayby + 3 deg....) than pitch attitude= AoA

[RealQuax]

@Hazelnuts39: I'm amazed. What prevented you from doing the appropriate thing and drop the nose half a degree or so?

I assume, you know the A330 and its related non-normal procedures: It says in QRH 2.21 "Respect Stall warning and disregard "Risk of undue stall warning" status message". In so far, you would be right. However, if you follow the whole procedure, crosscheck your Attitude/power-setting according to the table provided in 2.23, crosscheck with the GPS-derived speed and get the stall-warning nevertheless (BTW: with changing pitch angles) you consider the stall-warning invalid. Even the TRE explained that the simulator does not behave according to the manuals.

All I wanted to hint to is that sometimes the (aural) warnings created by the aircraft are adding up to the pressure you already have and should be able to be cancelled (e.g. by use of the emergency cancel-button, which did not work in this case...)

[24victor]

Doze.

Quote:

I know that the increased presence of computers in the flight deck is an emotive issue for pilots, but I can assure you that from the perspective of this software engineer, and, I'd be willing to wager even more - every software engineer who worked on the FBW aircraft that are flying today - we are on your side.

Amen. And thank you...

[engine-eer]

One problem that I see here with the Airbus approach to degraded mode operation is that the aircraft can be put into a flight mode that is not natural. In normal law the aircraft flies to a point in space where the pilot tells it to. In Direct Law the airplane is the same as a conventional aircraft, but in Alternate law the aircraft doesn’t have enough information to control the aircraft in a stable manner and it relies on the pilot for pitch stability. That is, when flying in normal mode the aircraft is controlled to point in the sky, and the autopilot system controls flight path by adjusting power and trim to match the control inputs of the pilot and the speed selected.

That’s all fine and good until something goes wrong with the inputs. When the control system goes into Alternate Law things get much more difficult. What I understand happens in that instance is that the pilot becomes the one who is controlling the aircraft in pitch and, the system is not stable in pitch. With a conventional trim system you set the trim angle and if you release stick pressure the aircraft will return to the speed required to match that pitch trim setting. This is the definition of a fundamentally speed stable system, remove the inputs and the aircraft goes back to a trimmed airspeed. With such a system, if the pilot made an incorrect input or responded to turbulence, all you have to do is relax stick force and the aircraft returns to a stable condition. With the Airbus the pilot must maintain pitch control with reference to the HSI and the trim will move around. Some of the Airbus pilots here say that isn’t excessively difficult, but it is surely a much higher workload to constantly keep the required pitch in the HSI while you are trying to fly through turbulence.

The Airbus system, in Alternate Law, will adjust the THS to “chase” the pilot inputs by changing the trim position. This is fundamentally unstable and consequently, unless you make absolutely no forward and aft inputs, the aircraft will climb or descend and the speed will increase and decrease. If the inputs are large enough and long enough, the trim will change and the aircraft will remain in a climbing or descending mode until the pilot applies input. It seems to me that Alternate Law without airspeed is really kind of a bastard system in that the control really doesn’t have enough information to fly the aircraft, so the pilot has to step in and provide stability.

In my opinion, the proper control system response to loss of airspeed information would be for the autotrim to be disabled at the same time as the autothrottle and set to the same condition as it was just before the autopilot dropped out. So I guess that in the case of loss of speed sensors I am thinking the system would be much better off in direct law.

Then the aircraft will be remain at a known pitch condition and therefore be speed stable. You don’t know what the speed is, but it was fine where it was and it isn’t going to change. The pilot then only has to control altitude with the throttle and keep the wings level and he is in a much safer place. If the pilot decides he wants more or less speed he can adjust the trim wheel to get it.

Somebody please correct me if I am wrong.

[DozyWannabe]

@ engin-eer:

The autotrim in Alt2 will only set the THS to "chasing" inputs if that input is held past the limits of elevator authority, otherwise it simply stays in the last position set when the FMC/autopilot kicked out. Letting the stick go in that situation will result in what you describe - i.e. the aircraft trimming itself back to it's stable position.

The only reason the autotrim moves to match pilot input is to give maximum control authority to a pilot in a significant upset without having to have his or her hands on both the sidestick and the trim-wheel. It follows that to have autotrim responding to sidestick inputs requires an emphatic stick movement held for some time.

[t54]

Quote:
t54 its pitch attitude and angle of attack being 16 degrees
its geometrie: in still air if the flightpath = chord angle (mayby + 3 deg....) than pitch attitude= AoA Yeah, I got that; but the flight path is horizontal at the top of the path.
You could only get pitch = AoA in horizontal flight if there is an upward wind.
Maybe there was and that's what helped to get the plane up there in the first place.

[Welsh Wingman]

Cross purposes, I think.

"
Welsh Wingman
"possible weather deviation limitations for this plane on this particular route (unless the flight crew want to land in Bordeaux and endear themselves to flight ops...)"

Weather deviations should cost peanuts in fuel quantity (ask your math teacher) so can we put this one to bed please... "

I didn't mean the particular de minimis deviation cost in this instance, but rather in the wider systemic issues that I was discussing. I was under the impression that this plane was close to MTOW at GIG and this route is close to its maximum range (never flown an A330-200 or any other Airbus before retiring in 1992, so not claiming any expertise), so merely hypothesising whether the BEA are hypothesising about the wisdom/relevance (if any) of even sending pilots into the ITCZ in the knowledge that a "major" weather diversion could mean a refuelling stop short of destination. I recall an old SAA friend telling me a few years back that some SAA pilots were frustrated at having to fly the A340-600 on the Joburg/New York route, when a longer range A340-500 would be perfect for the route if SAA had properly invested in the right equipment for the route.

Feel free to shoot this down, now that I have made clear. Not arguing that this is likely to be one of the major factors in the hull loss, but wouldn't yet discount it altogether from the overall mix in the context of not always giving equatorial CBs the healthy respect they deserve (unless I am wrong about my understanding of the range of the A330-200, which I accept that I might well be).

Not wanting to send anyone off on a wild goose chase.

I was thinking more about my old history teacher rather than my math teacher - divide-up the understanding of historical events into long-term causes (aviation industry focus?), short-term causes (aircraft manufacturer and/or aircraft operator focus?) and triggers (aircraft operator SOPs and flight deck focus?)....

[jcjeant]

Hi,

jcgeant
"Sorry if I'm dumb .. but .. someone can make a technical comment (explanation)
about the text in bold .. ?

From the 27 May BEA report:
Quote: Around fifteen seconds later, the speed displayed on the ISIS increased sharply towards 185 kt;
it was then consistent with the other recorded speed. The PF continued to make nose-up inputs. The airplane’s altitude reached its maximum of about 38,000 ft, its pitch attitude and angle of attack being 16 degrees."

That is puzzling. If the wing chord angle is zero it makes sense - the plane was moving horizontally through still air. I can't see how it can ever happen if the chord angle is not zero with a horizontally moving plane (which is implied by "reached maximum altitude"). Well I asked a explanation from pilots as I was puzzled by "Level 380" ... because this other A330 case (AF445) same sector .......

An Air France Airbus A330-200, registration F-GZCK performing flight AF-445 from Rio de Janeiro Galeao,RJ (Brazil) to Paris Charles de Gaulle (France), was enroute at FL380 overhead the Atlantic on airway UN741 just before waypoint DEKON about 680nm northeast of Fortaleza,CE (Brazil) and 750nm southwest of Praia (Portugal, Cape Verde), when the crew called Mayday on the international emergency frequency indicating, they encountered severe turbulence and were descending to a lower altitude. The airplane was seen enroute at FL280 overhead France and landed safely at Paris Charles de Gaulle 6:40 hours after the emergency call.

The Mayday call was relayed by the crew of a TAM Airbus A330-200 registration PT-MVG performing flight JJ-8055 from Paris CDG to Rio de Janeiro,RJ (Brazil) at around 03:50Z (Nov 30th). They were descending .. or they were stalling ?
Note that all recorded datas of this flight were never examined by any regulator or the BEA (AF was not able to produce those datas)

[rudderrudderrat]

@ engine-eer, I agree. In direct law I'd have a conventional Boeing with natural speed stability - perfect.

@ dozywannabe. Alt Law in pitch = "In flight, the alternate law pitch mode follows a load-factor demand law much as the normal law pitch mode does, but it has less built-in protection".
It doesn't sound much like direct law to me.

[Lonewolf_50]

Dozy:
I understand the advantages of autotrim, but I have reservations about the reason autotrim matches pilot input as explained here.
The only reason the autotrim moves to match pilot input is to give maximum control authority to a pilot in a significant upset without having to have his or her hands on both the sidestick and the trim-wheel.

Pilots have two hands. There are two pilots on the flight deck. Four hands. Autotrim available in an upset seem to me a very handy tool, particularly as the pilot (as I understand it) can override it via side stick commands.

Would it make sense that if one is in a Law or condition that calls for manual trim, that procedures would call for the PNF to be on the throttles as required/requested by the PF? That leaves PF with one hand on side stick and one hand on trim wheel.

I am in a CRM zone here.

That strikes me as how to avoid worrying about a two handed pilot having a three handed job, which you seem to allude to above.

Does the approach to this known possible condition vary between companies, or is there a generally agreed standard on how to deal with this in Direct law, upset or no?

[engine-eer]

The autotrim in Alt2 will only set the THS to "chasing" inputs if that input is held past the limits of elevator authority, otherwise it simply stays in the last position set when the FMC/autopilot kicked out. Letting the stick go in that situation will result in what you describe - i.e. the aircraft trimming itself back to it's stable position.

The only reason the autotrim moves to match pilot input is to give maximum control authority to a pilot in a significant upset without having to have his or her hands on both the sidestick and the trim-wheel. It follows that to have autotrim responding to sidestick inputs requires an emphatic stick movement held for some time.

Ok, I get it, he told the airplane to climb and it did. In this particular case Direct law would have been better than Alternate law since it wouldn't have trimmed him nose up, but if he hadn't held aft stick to the moon he wouldn't have been changing the trim either...

Somebody once said "it's hard to make anything foolproof because fools are so ingenious"......

[DozyWannabe]

@rudderrudderrat

I didn't say it was. You need to check the difference between Alt 1 and Alt 2. In this case they had Alt 2 + airspeed instrument failure, which pretty much nullifies stall protection. In any Alternate Law mode, the protections can be overridden if the stick input is firm enough and held for long enough. In short - in anything other than Normal Law, do not hold the stick back expecting the protections to have your back.

@engine-eer

Hi - cheers, but that's not what I'm saying. I don't know what he did (outside of the points in time mentioned in the BEA "note"), and neither does anyone else on this thread that I know of. I'm deliberately keeping any speculation to myself as much as I am able, because then I'd be no more useful to the thread than people who are saying that it must have been the pilots, the computer or even the weather. All I am saying is that the systems behave in such-and-such a manner if they are operating properly (i.e. as specified and designed).

[Mr Optimistic]

I am a bit puzzled about the concern about AoA indication. I presume maintaining what you guys call 'pitch and power' would probably have saved the day. If the climb was intentional then that's a step in the dark and the inability to adjust thrust to keep air speed up was the issue (not easy without airspeed reports). If the climb wasn't intentional but went unnoticed, seems unlikely that additional information on AoA would have been recognised. In the stall, if it wasn't recognised as a stal,l then what chance an AoA readout would have been noticed/acted upon. If it was recognised as a stall the -40 degree or so readout would have been irrelevant.

On another point, if the systems had some remaining degree of automation, given a pilot input of nose down, would it be so difficult for the system to recognise the intent, recognise the THS setting, and help him out by unfixing and adjusting it ? Seems a bit perverse to freeze the setting and not revisit it in the face of sustained pilot command.

[Garrison]

The total velocity unfortunately mostly downward was enough to fly and create lift, if they only where able to get the nose down in the flight pass direction.

Either the information provided by the BEA is inaccurate, or I have forgotten my trig, or there is a persistent misunderstanding on this thread about the attitude and flight path. The BEA report says pitch is 16 degrees nose up, 35-40 degrees angle of attack, and 10,000 fpm down. To get the flight path angle, you subtract the angle of attack from the positive pitch angle, giving around -20 to -25 degrees. The true airspeed is 10,000 fpm, or around 100 knots, divided by the sine of the angle, which gives around 250 knots. The airplane was in a stalled, mushing descent, not a vertical plunge or falling-leaf type of maneuver. At least this is what the BEA numbers require.

It appears to me -- with zero experience of flying this type of aircraft -- that recovery would not have required a great deal of height, once the wing was unstalled by trimming the THS and getting the pitch angle into the vicinity of the flight path angle, ie 20 degrees or so below the horizon.

[SaturnV]

jcgeant, see:
http://www.pprune.org/rumours-news/397440-air-france-severe-turbulence-mayday-call.html

see particularly mm43's posts in that thread

[Lonewolf_50]

If the climb wasn't intentional but went unnoticed, seems unlikely that additional information on AoA would have been recognised. In the stall, if it wasn't recognised as a stal,l then what chance an AoA readout would have been noticed/acted upon. If it was recognised as a stall the -40 degree or so readout would have been irrelevant.
Mr Optimistic, I respectfully disagree. Once you've used, or gotten used to, AoA as a gage, or been trained how to use it, it becomes another instrument you can go to for information ... like your engine instruments. Since the information it holds, stall or not stall, is somewhat important to flying ... "AoA high, lower the nose" isn't too hard of an association for a pilot to make. Hearing a stall warning tone is not the same as seeing your AoA. (For that matter, rudder shakers or stick shakers are another place where a sense other than hearing is used to cue a pilot that he is stalled or nearly stalled ... )
Either the information provided by the BEA is inaccurate or there is a persistent misunderstanding on this thread about the attitude and flight path.

The BEA report says pitch is 16 degrees nose up, 35-40 degrees angle of attack, and 10,000 fpm down.

To get the flight path angle, you subtract the angle of attack from the positive pitch angle, giving around -20 to -25 degrees.

This is the flight path angle, and it is far from vertical.

The true airspeed is 10,000 fpm, or around 100 knots, divided by the sine of the angle, which gives around 250 knots.

The airplane was in a stalled, mushing descent, not a vertical plunge or falling-leaf type of maneuver. At least this is what the BEA numbers require.
Presuming AoA is measured in degrees, not units, I follow what you are saying. The velocity seems to have been enough to return to flying if the nose could have been aligned with the flight path angle (presuming enough elevator/THS authority is available to get the nose pitching down).

Is that part of the point you are making?

[Garrison]

Yup. (+ six additional characters)

[Smilin_Ed]

Indication of the Angle of the THS: I doubt it would have helped.

Do I understand correctly that there is no THS position indicator?

If not, we have a situation where the "system" trimmed the aircraft into a stall, something we learned early on not to do, and yet the pilots had no indication of that.

[Lonewolf_50]

Sir, it seems that there is a THS indicator (visual), if one looks down at the trim wheels next to the throttle quadrants. My diagram (old) does not have enough fidelity to tell me how the wheels are marked.

http://avionique.free.fr/IMG/jpg/Cockpit_A330.jpg

That picture (if it is a faithful rendering of an A330 cockpit) shows me what looks to be an index, and large white blob (??) and what may be a scale in green.

Also recall in numerous threads comments about AB pilots needing to set the trim wheel to a particular value for takeoff (probably varies with gross weight??) So they'd need to be able to read the trim wheel's position to confirm their nose trim is at the value they calculated and require for takeoff.

[Mr Optimistic]

lonewolf: thanks. I am not a pilot so I am in no position to argue ! But if pitch, power and altitude rate were apparent and not taken due accord of.....?

[Golf-Sierra]

The maximum angle of attack (i.e. where the plane stalls) must depend on a number of factors - pressure altitude, airspeed, load factor, aircraft weight, config. Lots of points of failure for a measurement system.

I'm not sure if actually displaying a raw AoA it to the pilot would be so useful - otherwise every C152 would have such an instrument. How would the pilot know what is the current alpha-max?

The Airbus FCOM states that in case of a simultaneous OVERSPEED and STALL WARNING the stall is to be actioned - failsafe: if a pitot fault gives us an excessive speed the alpha-max will decrease, so if we follow the stall warning we basically end up flying a lower AoA then would otherwise be possible. But the 'under-speed' scenario does not seem to be addressed too well.

Now the types I am more familiar with - the C152 and DA20 - have a stall warning system which is basically an orifice on the wing connected by means of a tube to a little buzzer - it detects when the air pressure on the wing suggests an oncoming stall. This system is far superior to what the A330 has in one respect - it is completely independent of the airspeed system.

Now - why can't the Airbus/Boeing engineers devise such a system for the big jets? I do not suggests orifices, tubes and buzzers - rather - pressure transducers (or perhaps strain gauges?), a data transmission network and a clever computer to work out what is actually happening with the wing. A system which tells us if the wing is generating lift or not, how much lift, which part of the wing is stalled.

[Golf-Sierra]

The manual pitch trim is mechanically connected to the THS. That THS is pretty big.

Just out of curiosity - approx. how many revolutions of the manual pitch trim would it take to bring the THS from the max nose-up angle (12 degrees) to an angle where elevator authority is sufficient to command pitch down (8 degrees I recall). What about 0 degrees?

What force is required to move the pitch trim wheel? It says: "Mechanical connection", but is there some kind of power assist?

If the THS jammed, would the wheel also jam? Can icing cause the THS to jam?

What is the relation between manual trim and autotrim? If I manually trim does the autotrim disengage? When does it re-engage? What if autotrim is commanding nose up and I trim nose down - who has the last word?

[henra]

I think Flight Law at the time of Stall/descent was not auto trim, and would have required manual input on the two wheels bracketing the Throttle pedestal?

(See MartinM's great pic)

At the point of stall Flight law Auto- Trim was active for all that we know.
The only point where it might have reverted to manual was when Alpha = 30° was exceeded at around 2:11:35.
If the BEA 'leak' is correct Auto Trim was even active throughout the whole descent.

[Lonewolf_50]

Golf Sierra

The Navy aircraft I referred to earlier get around that with units ... not sure if that is applicable for transport aircraft.

Good points, also the understanding that AoA and stall AoA are not fixed values, but vary as you point out.

I am not sure I understand this.
The Airbus FCOM states that in case of a simultaneous OVERSPEED and STALL WARNING the stall is to be actioned - failsafe: if a pitot fault gives us an excessive speed the alpha-max will decrease, so if we follow the stall warning we basically end up flying a lower AoA then would otherwise be possible. But the 'under-speed' scenario does not seem to be addressed too well.

By "otherwise possible" do you mean "allowed by the protections" or physically possible? Is alpha max a computed value, or is it the raw AoA measured by the AoA probe?

My point is, if you have a false airspeed indication, the AoA probe/detector doesn't give a rat's behind. It is measuring something other than dynamic pressure, and if I may say, it is measuring something simpler: angle of airflow relative to the aircraft. (Or should I say airfoil?) Of course, if the AoA probe gets stuck/frozen rendered moot someway, then ... well, that's another dog's breakfast served to the flight deck crew. (Gee, it goes back to pitch and power again. :cool: )

EDIT: yes, there are two different hydraulic boost systems that help the mechanical linkage move the THS.

This picture (http://www.google.com/imgres?imgurl=http://msquair.files.wordpress.com/2010/03/aoa-rs-probes-a330.png&imgrefurl=https://msquair.wordpress.com/2010/03/21/integrated-vulnerability-and-qf-72/&usg=__WPS20GqQFNKDjqLoDvrMJ3IjJLo=&h=836&w=1098&sz=293&hl=en&start=48&zoom=1&tbnid=JSrQJh1nWrGz2M:&tbnh=165&tbnw=177&ei=WQroTYDxHMKugQfD6Y3LCg&prev=/search%3Fq%3Dangle%2Bof%2Battack%2Bprobes%2Bon%2Bairbus%2B33 0%26um%3D1%26hl%3Den%26biw%3D1008%26bih%3D694%26tbm%3Disch&um=1&itbs=1&iact=hc&vpx=340&vpy=367&dur=6094&hovh=196&hovw=257&tx=103&ty=86&page=5&ndsp=12&ved=1t:429,r:5,s:48&biw=1008&bih=694)purports to show A330 AoA probes, which look a lot like AoA probes I've seen on other aircraft. They do not measure what the pitot probes measure. What appears to happen inside the computer in the A330 is that airspeed input is compared to AoA probe reading is compared to other data and, once the calculations are done at the speed of electricity, visual cues are presented on the strips (vertical) next to the pilots attitude indicator on his flying display.

(VLS/V alpah prot V alpha Max)

[Machaca]

Golf-Sierra -- you may find this a good place to start:

http://www.smartcockpit.com/data/pdfs/plane/airbus/A330/systems/A330-Flight_Controls.pdf

[t54]

CogSim
I don't understand how you reach the idea of a stall warning based on an invalid (or even a valid) airspeed reading, since stall warnings are (should be?) based upon AoAStall is due to too an AoA which is outside the boundaries, but stall warnings are in addition due to your AoA being in danger of going outside the boundaries.
If your horizontal velocity is very low you have little lift (even if not stalled) and your downward component of velocity will increase so much that the AoA will go into the stall region.

[glad rag]

There was a reference [url] from JT to an earlier thread post from PJ2 detailing the 330 trim wheels on the pedestal the integrated read out of THS trim angle along with the follow up information available on the centre display, can't remember the actual display name 100% so will not say.
all the best

[Lonewolf_50]

t54, that was me, not cog sim, on that AoA tidbit.

FWIW, I see no reason to divorce stall warning from your AoA, but if you are working in raw angles versus units, I can see the issue becoming more complicated as the critical AoA is related to so many other factors. Thanks.

One way or another, be it at or beyond stall value, or "close to stall value, do something mate!" a suitable warning ought to be made.

If your horizontal velocity is very low you have little lift (even if not stalled) and your downward component of velocity will increase so much that the AoA will go into the stall region.
Uh, not quite, I am not sure I understand you there. You can go slow (low horizontal velocity) and level if you are not stalled, and go merrily without falling, or stalling.

That said, once you begin to descend, the second part of your sentence begins to make sense.

If what you are saying is that you are already falling, and have a low horizontal vector, then sure, the vector sums (depending upon rate of descent) change your AoA, and not necessarily for the better.

What has this to do with AoA indication or warning? AoA probe will measure how the air is flowing. (Direction)

[DozyWannabe]

Stall is due to too an AoA which is outside the boundaries, but stall warnings are in addition due to your AoA being in danger of going outside the boundaries.
If your horizontal velocity is very low you have little lift (even if not stalled) and your downward component of velocity will increase so much that the AoA will go into the stall region.

True.

I think we all have to be very careful to differentiate between the terms "Stall Warning", "Stall Protection" and "Stall".

The first can work to an extent without airspeed data but the second absolutely cannot. So if you get into the first or third in Alternate Law with no speed indication you are going to have to think very hard and work very methodically as quickly as you can.

[MurphyWasRight]

Mr Optimistic:

I am a bit puzzled about the concern about AoA indication.


While true that pitch and power would likely have worked something else -did- go wrong and the pilots ended up in a confusing situation.

At that poin a raw AoA indicator would have likely helped them to sort out
the counterintuitive return of stall warning as they were applying nose down.

In fact the stall warning in this case was a tragically misleading on/off AoA indicator that had 3 states:

Normal : silent
close to stall or stalled : STALL STALL STALL
severe stall : silent

Severe stall results in <60kt sensed speed and inhibition of warning.

This is not related to pitot ice/failure, it is a combination of true speed plus AoA effects on pitot as others have pointed out.

Had the raw data been avaiable they likely would have seen the AoA improving as the warning returned and pressed on with the correct recovery.

[engine-eer]

It appears to me -- with zero experience of flying this type of aircraft -- that recovery would not have required a great deal of height, once the wing was unstalled by trimming the THS and getting the pitch angle into the vicinity of the flight path angle, ie 20 degrees or so below the horizon.

Well, yes you could resume flying and generating lift, but you would be diving at a pretty severe angle and you have to generate enough G to turn the aircraft from that nose down path to horizontal. You have over 100 mph of vertical velocity and it's going to take some positive G to get rid of that. You aren't going to level out right away.

[Garrison]

Vertical velocity is 170 ft/sec, and a 2G pullout would subtract 32 fps from that every second. Let's say 6 seconds, during which you would lose quite a bit less than 1,000 feet. Doesn't sound as if pulling out of a 25-degree glide at 250 knots would take that much room. At low altitude it should be possible to pull 2G without risk of a secondary stall. The point is, despite its high vertical velocity the airplane is not descending that steeply.

[gums]

Sorry Garrison, but you must add the pitch attitude to the AoA to get the descent angle.

At impact, we know the BEA figures for 107 knots horizontal and vertical. Another contributor came up with same numbers I did, which was a basic 45 degree flight path with a 16 deg pitch attitude at impact. So AoA would have been around 61 degrees. When I use 107 knots vertical, I get about 10,800 feet per minute vertical vector, which seems to agree with BEA's numbers.

The last recorded values were a pitch attitude of 16.2 degrees nose-up, a roll angle of 5.3 degrees left and a vertical speed of -10,912 ft/min.
I point out the close agreement with my back-of-the-envelope calculations concerning vertical velocity

I can't find a BEA data point of 16 degrees pitch attitude and 35 - 40 degrees AoA in their report.


more on "trust your AoA" later for those debating its value when airspeed is FUBAR.

[t54]

Lonewolf_50

T54
If your horizontal velocity is very low you have little lift (even if not stalled) and your downward component of velocity will increase so much that the AoA will go into the stall region.

Uh, not quite, I am not sure I understand you there. You can go slow (low horizontal velocity) and level if you are not stalled, and go merrily without falling, or stalling.

That said, once you begin to descend, the second part of your sentence begins to make sense.

I'm just looking for the cause of the two stall warnings right at the start, using the hypothesis that a stall warning is triggered not only by AoA but also when the (indicated) air speed falls into a region where a stall in level flight is imminent.

The further conjecture is that the PF acted on these (spurious) warnings according to the manual, and in doing so, perhaps in conjunction with an unfortunate updraft, got himself into a real stall.

So the invalid stall warnings helped get them into a real stall - and the lack of stall warnings (plus the resumption of warnings at times on correct pilot input) when they were in the real stall minimised the chance of them ever getting out of it.

Just a thought.

[Alison747]

Excuse me for interjecting in a technical discussion as mere SLF (even if it is one who sits on an A340 across the pond rather often):

I am conscious of the various discussions about presence or absence of an AoA indication, and have read this entire thread from day 1 (sad?).
My personal background started in mathematics, moving into engineering, including the much maligned real-time software.

Anyway - a couple of comment on "vector maths", which most pilots should be familiar with from route planning?

If we assume that "pitch and power" were to be maintained, we would have an aircraft with pitch which was likely to be based on inertial reference. At this time, I believe this has not been questioned. A previous post then said that "pitch = airspeed, power = altitude". This makes sense, although I confess I have not had time to search back for the quote (credit to the author, never the less).

Then to the next stage - if you have pitch with reasonable reliability, the AoA is likely to be close to the vector sum of the forward and vertical velocities (not accounting for upward or downward air movement)

Hence - if you have reasonable, or at least some, indication of pitch and a large downward vertical velocity then do you not have a fair indication of a possible stall? The alternative is a very strong updraught - but how long is that likely to last?

Just a thought, I wonder if it is relevant?

[Garrison]

Sorry Garrison, but you must add the pitch attitude to the AoA to get the descent angle.


Not on this planet. You have to add the pitch angle to the negative of the flight path angle to get the angle of attack (assuming that the flight path angle is negative for a descent).

With regard to the descent angle, the BEA report I am reading (27 May) says 15 to 16.2 degrees deck angle. At 35,000 feet, on the way back down, the angle of attack exceeds 40 degrees but during the 3+30 descent the angle of attack "remained greater than 35 degrees". Now, I suppose you could argue that "greater than 35" means 65, but the use of "exceeds" and "remained greater" strongly suggests that the AoA remained in that neighborhood -- that is, "greater than 35" means 36 or 37, not some much larger number.

I concede that the 107-knot groundspeed at impact is inconsistent with my calculation of 250 ktas, unless there is an improbably huge surface wind; but it is also inconsistent with the reported pitch angle and angle of attack. Maybe something changed in the final seconds; I don't have a good theory handy.

[bearfoil]

I haven't flown one in many years, but the Stall Horn on the 150 series I believe is nothing BUT an AoA indicator, albeit "aural". Zeroed to exclude angle of Incidence, (the from factory difference in chord line and fuselage longitudinal line) the horn starts to mouth off when air "leaves" the orifice. This I know for I used to test it by inhaling on the hole, and depending on effort, I could almost play it like a flute. Blowing into it accomplishes nothing. When the ANGLE of the airstream starts to impinge on the orifice at a suitable positive AoA, the annoying alert starts to pucker one's own orifice, more so as the AoA approaches the Stall Break.

Dozy. I am in earnest about evidence, something I define as facts, as do you.

Likewise, at Court, facts come with a guarantee, something lacking here.

You are not incorrect in your explanation of the Laws, I believe in you completely. Thus far, the bulk of trouble some have here is not in disallowing the Program, or its influences, but in the arena of suitability in crisis. This unsuitability is in discussion, and I warrant it has a basis in fact. something you seem unable to entertain.


I repeat. IF, upon selling a suite of hardware, one does not exhaustively train its usage to the client, one has sold a bill of goods.

one outsider. Please accept my offered apology for twaddle. I agree, though I think your Twaddle Launcher is pointed at the wrong target, just sayin'.

Garrison Absent any need for Pitch or AoA at impact, the Horizontal and Vertical velocities sum for a FLIGHT Path of 45 degrees descent Yes? One wishes for a mental picture of "almost" airborne, but BEA pitch at 16 and AoA at 35 + is discouraging.

ADD. I get an airspeed of about 135-145 knots (at impact) if BEA'S numbers for rate are accurate.

[A33Zab]

PVT

In the Flight Global article, they are making the distinction that the aircraft never went into the abnormal attitude law because the flight computer had rejected the information coming in from the ADRs before those parameters were met. The aircraft was already in alternate law from the loss of airspeed. The last underlined part is saying that the flight computers would have to see 'acceptable' data from the ADRs to trigger this law like the examples given.


If AOA is available for FDR it should be available for other systems too (benefits of ARINC429),
I've read in system schematics that there is a separate AOA backup signal bus to FCPC's.
On second thoughshould have been activated by AOA >30 @ 2h 11 min 40 ts that may be only on –BUSS- equipped A/C.
I'll come back to you if I got that in hand.

Besides that, if you combine the 3 BEA reports together, the Abnormal Attitude Law before NAV ADR DISAGREE warning msg @2h 12. (Received 2h 12 51)

@Bear:

Don't change the rules and call it something it ain't.

Just trying to clear some operational 'misunderstanding' of FBW and laws from an E&M point of view. If not appreciated just say so.

http://i474.photobucket.com/albums/rr101/Zab999/ManPitchWheel.jpg


@Dozy:

Agree with you.

[Smilin_Ed]

As I have posted a couple of times before, AoA is highly useful at approach speeds (and in a stall situation) but not for maintaining a desired flight condition while in cruise. When encountering an Unreliable Airspeed condition, flying a specified AoA would not be very effective in cruise. At approach speeds, AoA varies relatively large amounts for relatively small changes in airspeed. At cruise speeds, the variation of AoA is relatively small for relatively large airspeed changes.

The U.S. Navy uses AoA for landing on aircraft carriers because it provides a precision reference for executing a precise approach. AoA indicators have not typically been used in transport category aircraft because that degree of precision is not required, but flying AoA does allow the pilot to fly the correct approach airspeed, regardless of weight and without reference to tables. The P-3, as initially introduced into the fleet, was equipped with AoA indicators but they were routinely ignored because "AoA is for jets". I don't know if those AoA indicators are ever used today.

IMHO, AoA is the single most useful instrument you can have to prevent a stall.

[Garrison]

at impact, the Horizontal and Vertical velocities sum for a FLIGHT Path of 45 degrees descentYes?

Yes, and with 16 degrees nose up that gives an AoA of 61 degrees as asserted by gums. But the BEA numbers for most of the descent -- pitch 15, AoA 35-40 -- imply a much shallower descent. The airplane was almost uncannily stable during much of the descent -- steady AoA, no spin, and 40-degree wing rock correctable with ailerons is pretty nice behavior with AoA > 35 -- but that may have changed. It is not clear to me whether thrust went above idle again after 2:12:02; at low altitude thrust could affect angle of attack.

[bearfoil]

Garrison

Bear says:

Quote:
at impact, the Horizontal and Vertical velocities sum for a FLIGHT Path of 45 degrees descentYes?

Garrison says:

Yes, and with 16 degrees nose up that gives an AoA of 61 degrees as asserted by gums. But the BEA numbers for most of the descent -- pitch 15, AoA 35-40 -- imply a much shallower descent. The airplane was almost uncannily stable during much of the descent -- steady AoA, no spin, and 40-degree wing rock correctable with ailerons is pretty nice behavior with AoA > 35 -- but that may have changed. It is not clear to me whether thrust went above idle again after 2:12:02; at low altitude thrust could affect angle of attack.

Sorry, how is 55 degrees a much shallower descent than 61?

I am using BEA derived data re: velocities, basically H/V square. That gives a very simple Pythagorean solution of 45 degrees for hypotenuse, and velocities (integral) that compute to a summed velocity of 140 knots or thereabouts. I don't disagree with your assumption that these figures were or could be different at altitude, but so far no data with which to invest in an opinion?

[mm43]

For those who need some help in envisaging what a high Angle of Attack looks like and how it will affect the pitot data, the following graphic should help.

http://oi51.tinypic.com/201mky.jpg

It should also be noted that during the final stall, the AoA was never less than 35 degrees, and this was probably only achieved with N1 100%, with the AoA increasing once engines were at idle.

[bearfoil]

"It should also be noted that during the final stall, the AoA was never less than 35 degrees, and this was probably only achieved with N1 100%, with the AoA increasing once engines were at idle."

Que?

[Garrison]

Can anyone clarify for me the operation of the AoA system? The real angle of attack must be obtained from a lookup table that translates the vane position into actual alpha. How far does the lookup table go? The interim report says that (my translation) "The angle of attack, when it is valid [or reliable], remains above 35 degrees." (Emphasis mine.) What limits the validity of the reading? Is the AoA recorded by the FDR and reported by the BEA valid/reliable for purposes of visualizing the attitude and flight path of the airplane?

[mm43]

Que?

If the horizontal component increased due to additional power and the RoD remained essentially the same, the AoA will have decreased. Do you want me to stretch the graphic to prove it?

[Garrison]

bearfoil...
Sorry, how is 55 degrees a much shallower descent than 61?


I feel like Alice in Wonderland, except I'm a guy.

It's not 55, it's 25. Please please please draw a picture of an airplane, side view, nothing fancy, with its nose tilted upward 15 degrees. Then take a protractor and draw a line at a 40-degree angle downward from the airplane's longitudinal axis (which stands in, for purposes of discussion, for the mean aerodynamic chord). That is the flight path angle -- definition of angle of attack. It's 25 degrees.

Granted, the BEA numbers could be wrong -- garbage in, garbage out.

Maybe I should draw the picture. I'm not very good, but I'll try.

[bearfoil]

I think mm43's picture is cool, have you seen it? The long line is the Flight Path, from data via BEA. That qualifies as (Angle of) descent for me. Pitch and AoA are important how? Ride?

bear

mm43, hey two against one, no fair. With N1 100 %, doesn't the Pitch increase? and since increasing Pitch separates the AoA , it increases also? Lowering Thrust therefore closes the two (or...... This is a ballistic projectile. A brick with fins.

[Garrison]

How do you post a picture? I drew one, it's a JPG, but I don't know how to insert it into a message. The "Insert image" icon asks for a URL.

[bearfoil]

MAC? maybe it's in Direct Law. You are entertaining a ballistic projectile, yes?

airfoilmod@sbcglobal. net. attachment?

I'm looking at 15 seconds before, and fifteen seconds after a/p disconnect. Here is where it happened.

[gums]

Sorry, all, I misplaced two of the vectors in my explanation. So I'll stick with my story, and only place I find a no-kidding AoA and pitch attitude and both velocity vectors was the one I quoted from the BEA report.

This is what I was trying to depict.

http://i120.photobucket.com/albums/o196/gatlingums/aoa.jpg

As shown here on my chalkboard, the AoA is the sum of the pitch attitude and the velocity vector ( assume airflow is opposite the velocity vector in the air).

Bear is correct about total velocity, 'cause if both horizontal and vertical velocities were identical, the total vector would be about 1.414 times either of them ( square root of two).

Need a real geometry wizard to make the call. Winner ( and referee) gets a free slug of Jeremiah Weed at my fishing cabin in Colorado in a few weeks.

I throw my hat in with the AoA mafia.

I don't understand why it isn't used more often, as it reflects the basic characteristics of the wing and its lift capability. In other words, weight of the jet is inherent, as the AoA must be greater to get the extra lift for the same speed. High lift devices, flaps, etc can change the stall AoA value, but that's an easy thing to depict on a display.

I call 'bird to the stand re: AoA indexer and gauges for the Navy jets.

Hate to hijack the thread from the "who was in what seat" discussion, but thot we could use a break.

[bearfoil]

That pitcher, that one.........

Pitch and AoA are important how? Ride? What is the AoA in flat Plate?

[Tailspin Turtle]

Or for simple folk... http://img.photobucket.com/albums/v354/ththomason/A330Diagram.jpg Note that the ground speed for the given pitch angle, angle of attack, and 10,000 fpm rate of descent is about twice the BEA number...

[Garrison]

Whew! Thanks a million. But what do you mean about 10,000 fpm being twice the BEA number? It is the BEA number.

[gums]

Yeah, Tailspin, just show for the impact velocities BEA has published.

I also got the same numbers using an AoA of 40+/- and pitch of 16 and vertical of 10,000 feet per minute

For Garrison: He says the groundspeed, not the vertical velocity. He is also using some numbers from early in the description of the descent. I am using the ones at impact, which are very specific in the report.

[bearfoil]

That pitcher, that one.........

Pitch and AoA are important how? Ride? What is the AoA in flat Plate?

I am still stuck on Flight Path, ok? Ballistic flightpath. Not "line of Flight" when there is none.

Ballistic. Some few seconds after 2:10:04, Aero was out the door, and Rocketry wandered in. Ballistic.

Rocketman? Where fore art Thou?

[Garrison]

Yeah, Tailspin, just show for the impact velocities BEA has published.

Well, that's the point. The numbers BEA gives for the steady-state descent are incompatible with the groundspeed at impact. Either something changed at low altitude, or the numbers are not reliable.

[bearfoil]

I think, as above, what went out the glass ("changed at altitude") was aeronautics, at ~ FL360.

One cannot fly a brick, no matter the architecture. And Stall is a point in time, once broken, Stall is left behind. It is Flight, Stall, or NOT Flight. At no time can two of the above be happening concurrently. One at a time. "Breaking the Stall" is misleading, what one does, is become airborne again. "Take off".

How's that for pedantic. Garrison, you are a writer, does that work for you?

Barkeep, two aspirin and an ROC cokola, boy howdy.

[mm43]

The numbers BEA gives for the steady-state descent are incompatible with the groundspeed at impact. Either something changed at low altitude, or the numbers are not reliable.The graphic I put up on the previous page is using the BEA's data at impact. You are not telling me they read that data out incorrectly?

[bearfoil]

mm43

and my velocity was low by 11knots. Apologies, and good night.

[Machinbird]

Smilin_Ed (Another USN guy)
IMHO, AoA is the single most useful instrument you can have to prevent a stall. And also the single most useful instrument in recovering from a stall. Otherwise, at low speed, how do you know how much to push the nose down? Suppose you are actually inverted? Which way do you pull (push) then?

I didn't always look at my AOA while flying my Navy jet, but if I was maneuvering, it was definitely in my scan. If you ever get AOA in your airliner, try real hard to use it. You don't need it in cruise of course, but when you start to dirty up, you can observe the beneficial effects of slats and flaps very clearly, and with a little practice, you can tell when you need some flap to fly slower.

How to best mechanize AOA presentation has some contention, but it is probably time to develop a standard for airliners. It would be silly to have to train to recognize different types of presentations for each aircraft you fly.
A little bit of software and some free space on your PFD should be all most jet aircraft will need.

The AOA gauge directly answers the question, "How close am I to stalling the aircraft. " You can accurately fly an aircraft below stall speed in a ballistic trajectory and not stall the aircraft if you mind your AOA. (Of course, you do need some control authority-this doesn't work with tail slides.:})

I'm also thinking the first two "beeps" of stall warning on AF447 were quite possibly caused by the g incurred in the initial pull up! It will be interesting to see the pitch rates developed.

[JD-EE]

deSitter, two comments about that link about demanding all A330s be grounded:
1) It's Speigel, which news service does not have a sterling reputation for their handling of this crisis, so far.
2) The A330 has a safety record that any earlier airliners more than a few years older than the A330 can only dream about. Shutting it down on a 1 in a million accident is past foolish. It's damn foolish.

I'm tempted to add a third item - it's Spiegel.

[Garrison]

I wish there were some aero guys contributing to this thread. It's interesting, and revealing, that a bunch of Airbus pilots hunched over their keyboards in the safety of their homes can argue so long and hard about the meaning of the various "laws"; imagine trying to figure it out in a cockpit headed toward the ocean. But the laws that really count in the end are the laws of nature and physics, and I think a lot of the commentary here has been lacking in understanding of the aerodynamics of a stalled airplane. It's much more complicated than just "brick". It appears that the wing is providing sufficient downwash, in spite of being "stalled," to keep a download on the horizontal stabilizer. If it were not, the airplane would pitch down naturally, because it is a conventionally configured airplane, it's not in a spin, its CG is not excessively far aft, and that's what they do. So the stabilizer is actually working. Furthermore, the wing, although largely stalled -- but note that the ailerons continue to be effective -- is still producing a lot of lift -- probably a CL of 1.0 at least -- but just with a ton of drag to go along with it. It's the drag that's making the airplane sink -- not lack of lift.

I'm just an amateur at this, but I've talked with a few experts and they all agree that it's highly unlikely that the airplane was in a stable "deep" stall. Much more probable that it was being held nose-high by its own wing and stabilizer.

[Machinbird]

Bearfoil
One cannot fly a brick, no matter the architecture. ....Bear, I used to fly a brick-like object aboard ship routinely. The secret was maintaining control.:}:}:} Well, that and lots of thrust too.

[Garrison]

mm43
The graphic I put up on the previous page is using the BEA's data at impact. You are not telling me they read that data out incorrectly?

No no, your graphic is great (don't quite agree about pitot behavior, but that's a small matter when they're frozen anyway) but if you compare it with Turtle's you see that the two sets of numbers are incompatible. So either some of the numbers are wrong to start with, or the flight conditions changed as the airplane neared the surface.

[Tailspin Turtle]

My bad. The BEA report doesn't give an angle of attack at impact. Solving for it: http://img.photobucket.com/albums/v354/ththomason/A330DiagramGroundSpeed.jpg

[bearfoil]

Hello, bingo.

[mm43]

bingo!Two graphics showing exactly the same data, just in different ways.;)

[Garrison]

mm43
Two graphics showing exactly the same data, just in different ways.

You mean your graphic and his second one. Agreed. I'm talking about the differences between his first one and his second one, which are quite significant.

[Tailspin Turtle]

You mean your graphic and his second one. Agreed. I'm talking about the differences between his first one and his second one, which are quite significant.

Consider my first graphic to be the general case on the way down and the second to depict the flight condition at impact with the difference being the angle of attack. Of course, the actual angle of attack at impact will be dependent on surface wind speed and direction, but it was clearly much more than 40 degrees for the stated rate of descent and ground speed at impact and might even have been more than 61 degrees.

[Graybeard]

The modern jetliner gets its vertical speed from the IRU, Inertial Reference Unit. The IRU measures in 3 axes, as that's how the plane travels. It is apparent that all the velocity was in the Z axis, so the plane was dropping at 10,912 fpm, or 107 knots. There must have been near zero horizontal velocity when the plane hit.

AOA vane has physical stops. It has to be 35-40 degrees, so greater than 40 degrees AOA can only be calculated from the IRU, which data has apparently not been released, and the BEA are quoting AOA only from the vanes. I'm betting real AOA at the end was 100-120 degrees.

[mm43]

If you go back to Tailspin Turtle's last graphic, it is easy to see that the airflow around the empennage and over the THS will create a turbulent mush over the rudder, making the rudder IMO useless.

[JD-EE]

gums, I figure your geometry is correct. And I suspect the AoA vane was at one of its stop positions. Given the phrasing it hits a stop not far beyond 35 degrees.

[JD-EE]

Garrison, if you're going to round the number it was 11,000'/min.

[mm43]

Graybeard
... so the plane was dropping at 10,912 fpm, or 107 knots. There must have been near zero horizontal velocity when the plane hit.
The BEA gave two components:-
... vertical speed of -10,912 ft/min, a ground speed of 107 ktsSo, I don't understand how you have determined the near zero horizontal velocity.

[JD-EE]

Bearfoil
Quote:
One cannot fly a brick, no matter the architecture. ....
Bear, I used to fly a brick-like object aboard ship routinely. The secret was maintaining control.http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/badteeth.gifhttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/badteeth.gifhttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/badteeth.gif Well, that and lots of thrust too.

(cough)(cough) With enough power you can fly a brick or perhaps more prosaically a lawnmower. Search for the flying lawnmower video on YouTube. It's hilarious. And it flies pretty well, too.

[Capn Bloggs]

There must have been near zero horizontal velocity when the plane hit.

I'm not so sure. Unless it was a fluke, the ship hit the water with 5° of bank, which indicates to me that the crew had roll control ie semi-effective ailerons. Had it been going straight down, no useable flow over the ailerons would have existed and it probably would have been falling like a leaf or tumbling.

100kt down and 107 G/S means it was "flying" at 140KIAS, albeit at 60° AoA.

[Machinbird]

MM43
If you go back to Tailspin Turtle's last graphic, it is easy to see that the airflow around the empennage and over the THS will create a turbulent mush over the rudder, making the rudder IMO useless.It might not be quite that bad. Put 13 degrees of THS leading edge down on that THS and it doesn't block the rudder quite so badly. Also, even past the stall angle of attack, the inboard sections of a swept wing (or THS) are not as badly stalled as the sections further outboard. The VS & rudder being near the centerline should keep them in more energetic flow than it might initially seem.

Thinking about relative effectiveness of the wing and THS, the THS will operate closer to its intended operating point than the wing and thus its C/L should be less affected than the wing's. I.E. With a trimmed up THS (Leading edge down), the THS should become more effective in overpowering the wing pitching moment.
I don't do Aero , so any real Aero's on the thread can comment without hurting my feelings. If correct, that might explain why the stalled aircraft does not want to pitch down. That and the tendency of the center of lift to move forward on a stalled swept wing.

[PickyPerkins]

History
One of the more interesting (to me) on-line documents relating to the history of recommendations concerning the use (or non-use) of trim during recovery from upsets in transport aircraft is a talk given by Captain William Wainwright, Chief test pilot of Airbus.

The full text is available from at least two sources (one being the NTSB).
http://www.ntsb.gov/Events/2001/AA587/exhibits/240005.pdf
http://www.skybrary.aero/bookshelf/books/435.pdf

Here are some extracts. The omission of text in these extracts is indicated by “………”.

--------- Start of quote extracts -----------
AIRPLANE UPSET RECOVERY TRAINING AID,
By Captain William Wainwright, Airbus Industrie.

INTRODUCTION
The idea for a joint industry working group to produce an Airplane Upset Recovery Training Aid was first proposed by ATA in June 1996. ........ The end result of 2 years work is a training package including a video and a CD-ROM, giving an airplane upset recovery training aid. This package is on free issue to all of you, to use or not to use as you wish. ………..The content of the package is not my subject today, but there are a few issues of general interest which I gained from my experience as a member of the working group which I would like to talk about.

2. THE BEGINNING
…… Right from the beginning there was a conflict between the technical advice given by the manufacturers' training pilots and that expressed by those of the principal airlines already practicing upset training. They naturally considered themselves to be the experts on this subject, based on the many .hours of training that they had already conducted on a large number of pilots in their simulators. At the beginning of 1997, the Flight Test Departments were asked to come in to support their training pilots. From then on, the chief test pilots of the 3 major manufacturers became members of the working group; XXX of Boeing, YYY of McDonnell-Douglas (now Boeing - Douglas Products), and myself. But the conflict over the different opinions on aircraft handling and recovery techniques continued for a long time until we finally achieved agreement at the last meeting in January 1998. The reasons for these differences of opinion are the subject of my talk today.

3. THE DIFFERENCES
The differences of opinion were mainly concentrated in the following areas:
(a) Procedures versus general advice.
(b) Ease of training versus failure cases.
(c) Stalling.
(d) Use of rudder.
(e) Use of simulators.

It is worth saying that there was never any difference of opinion between the three test pilots on the group. Although we come from different backgrounds and have worked in different organizations with different work cultures, we always agreed on our technical advice.

4. PROCEDURES VERSUS GENERAL ADVICE
The airlines wanted simplified procedures which were common to all aircraft in their fleets and which were easy to teach and easily reproducible. This is understandable because you are all interested in having a standard product at the end of your training programmes. And this is what they already had with the Airplane Upset Recovery Training that they were already doing. For the training managers from American Airlines, Delta, and United, the only thing necessary was to give an overall industry approval to their existing programmes; they already worked, because the many pilots that had undergone training all came out of it with the same standardized reactions to the standard upsets. For them, this was the necessary proof that their training programme worked.

Where we differed was in our conviction that there was no such thing as a standard upset and our reluctance to endorse simplified procedures for recovery from an upset. We wanted a general knowledge based approach, as opposed to a rule based one. For this, after proposing some initial actions, we talk about “additional techniqlies which may be tried”. This obviously is more difficult to teach. ...........

5. EASE OF TRAINING VERSUS FAILURE CASES
The training that was already being done considered upsets as being due to momentary inattention with a fully serviceable aircraft that was in trim when it was upset. We would like to consider other cases that involve failures of control systems or human errors leaving the aircraft with insufficient control authority for easy recovery.

This of course complicates the situation, because recovering an aircraft which is in trim, possessing full control authority and normal control forces, is not the same as rocovering an aircraft with limited control available or with unusual control forces. Thus, for us, an aircraft that is out-of-trim, for whatever reason, human or mechanical failure, should be re-trimmed. Whereas the airline instructors were against the use of trim because of concerns over the possibility of a pilot overtrimming and of trim runaways which are particularly likely on some older aircraft types which are still in their fleets. We spent a lot of time discussing the use of elevator trim, and we never reached agreement. All the major US airlines were adamant on their policy to recover first using “primary controls” which excluded any reference to trimming. Again, a compromise was necessary. What we have done is to talk about using trim if a sustained column force is required to obtain the desired response whilst mentioning that care must be used to avoid using too much trim. And, the use of trim is not mentioned in the simplified lists of actions to be taken.

6. STALLING
Another aspect that was 'being ignored in the existing training was the stall. By this I mean the difference between being fully stalled and the approach to the stall. In training, you do an approach to the stall with a recovery from stick shaker, which is often done by applying full thrust and maintaining existing pitch attitude in order to recover with minimum loss of height. Height cannot be maintained if an aircraft is actually stalled and should be of secondary importance. .......

There is a world of difference between being just before, or even just at, the stall, and going dynamically well into it. The training being given in the airlines at the time to recover from excessive nose-up pitch attitudes emphasised rolling rapidly towards 90" of bank. This is fun to do, and it was not surprising to find that most of the instructors doing the training were ex-fighter pilots who had spent a lot of time performing such manoeuvres in another life. The training was being done in the same way, with an aircraft starting in trim with a lot of energy and recovering while it still had some. However, the technique being taught only works if the aircraft is not stalled. ……..
If the airplane is stalled, it is imperative to first recover from the stalled condition before initiating the upset recovery technique. Do not confuse an approach to stall and a full stall. An approach to stall is controlled flight. An airplane that is stalled is out of control and must be recovered.
A stall is characterised by any, or a combination of the following:
--- Buffeting, which could be heavy at times.
--- A lack of pitch authority.
--- A lack of roll control.
--- Inability to arrest descent rate.
To recover from a stall, the angle of attack must be reduced below the stalling angle. Apply nose down pitch control and maintain it until stall recovery. Under certain conditions with under-wing mounted engines, it may be necessary to reduce thrust to prevent !he angle of attack from continuing to increase. Remember, in an upset situation. If the airplane is stalled, It is first necessary to recover from the stall before initiating upset recovery techniques. This is something that we are well aware of in testing, but it was either being totally ignored, or misunderstood. I consider the inclusion of this note to be one of our most important contributions.

8. USE OF SIMULATORS
We manufacturers were very concerned over the types of manoeuvres being flown in simulators and the conclusions that were being drawn from them. Simulators, like any computer system, are only as good as the data that goes into them. That means the data package that is given to the simulator manufacturer. And we test pilots do not deliberately lose control of our aircraft just to get data for the simulator. …………..

The complete data package includes a part that is drawn from actual flight tests, a part that uses wind tunnel data, and the rest which is pure extrapolation. If should be obvious that conclusions about aircraft behaviour can only be drawn from the parts of the flight envelope that are based on hard data. This in fact means being not far from the centre of the flight envelope; the part that is used in normal service. It does not cover the edges of the envelope. I should also add that most of the data actually collected in flight is from quasi-static manoeuvres. Thus, dynamic manoeuvring is not very well represented. …………

In other words, you have reasonable cover up to quite high sideslips and quite high AOAs, but not at the same time. Furthermore, the matching between aircraft stalling tests and the simulator concentrates mainly on the longitudinal axis. This means that the simulator model is able to correctly reproduce the stalling speeds and the pitching behaviour, but fidelity is not ensured for rolling efficiency (based on a sirrpfified model of wind tunnel data) or for possible asymmetric stalling of Ihe wings. ......

In fact, this is a perfectly adequate coverage to conduct all normal training needs. But it is insufficient to evaluate recovery techniques from loss of control incidents. Whereas, the training managers were all in the habit of demonstrating the handling characteristics beyond the stall; often telling their trainees that the rudder is far more effective than aileron and induces less drag and has no vices In short, they were developing handling techniques from simulators that were outside their guaranteed domain. Simulators can be used for upset training, but the training should be confined to the normal flight envelope; For example, training should stop at the stall warning. They are "virtual" aircraft and they should not be used to develop techniques at the edges of the flight envelope. This is work for test pilots and flight test engineers using their knowledge gained from flight testing the "real" aircraft.
--------- End of quote extracts -----------

[rubberband2]

(cough)(cough) With enough power you can fly a brick or perhaps more prosaically a lawnmower. Search for the flying lawnmower video on YouTube. It's hilarious. And it flies pretty well, too by ....... JD-EE

Here is the magic of lots of power and a good prop slipstream to help the flying controls to work aerodynamic wonders and lighten our day!

YouTube - &#x202a;Flying Lawnmower&#x202c;&rlm;

[Litebulbs]

The BEA gave two components:-
So, I don't understand how you have determined the near zero horizontal velocity.

10,912 fpm is, give or take 107kts, which would be some coincidence. Residual ground speed anyone?

[susu42]

Simple trigonometry: if the speed vector is at a 45 degrees angle then vertical speed is equal to horizontal speed.

[infrequentflyer789]

Didn't the BEA permit AB to make a statement that they believe nothing needs to be modified in the A330 after the black box data was reviewed?


No, the AB statement was that no modifications (other than previously advised) were required yet - ie. the further investigation of the data may result in modification requirements


If that is true, BEA must believe it was a pilot only problem; right?

It isn't true, but that doesn't disprove that statement. I would hope however that until any other (than pitot) possible aircraft failures are eliminated, the conclusion remains open - and that will take a lot of work analysing the data.

[sensor_validation]

...100kt down and 107 G/S means it was "flying" at 140KIAS, albeit at 60° AoA.

What about windspeed?

Pedantic maybe, but 140KTAS or 140KCAS. If the pitots only observe the normal component they may only report an "unbelievable" 70KIAS. With wind and sidelip it is easy to see the IAS from any/all unfrozen sensors moving across the 30-60kt range and responsible for initiating/blanking alarms.

Pitot tubes are designed to have little effect over +/-20 degree range, higher than this is possible with 'shroud' extensions

[HazelNuts39]

I'm also thinking the first two "beeps" of stall warning on AF447 were quite possibly caused by the g incurred in the initial pull up! It will be interesting to see the pitch rates developed. The stall warning AoA at M=0.8 gives you about 1.4 g. But then the BEA Update says 11 second later at 2:10:16 "The airplane's pitch attitude increased progressively beyond 10 degrees and the plane started to climb".

[rudderrudderrat]

At 2.10.05 when the autopilot dropped out, due unreliable air speeds (showing about 60 kts), if the system had gone straight into Direct Law the aircraft would presumably have remained "speed stable" provided the elevator was not moved.

Would Direct Law be easier to handle with unreliable air speeds than Alternate Law?

[BOAC]

if the system had gone straight into Direct Law the aircraft would presumably have remained "speed stable" provided the elevator was not moved. - an assumption only, based on no idea what the a/c was actually doing at the time!Would Direct Law be easier to handle with unreliable air speeds than Alternate Law? - come on now, you claim to be a 320 pilot. Surely you know that that would run counter to all AB philosophy of 'protecting' the machine? The software know best, you, the pilot, do not need to know.:ugh:

[rudderrudderrat]

Hi BOAC,

Normal Law is brilliant. It wraps the aircraft in cotton wool.

Direct Law is just like a Boeing and I could cope with that.

Alternate Law is something in between.

During unreliable air speed whilst the crew held the wings level using constant left roll input, but with a mistaken light back pressure, it trimmed the aircraft fully nose up in response - without them realising. That's bad.

[BOAC]

I quite agree but am pointing out that the philosophy change, in ceasing to 'protect' the aircraft from piloting, at AB, would be too dramatic

[sensor_validation]

gums, I figure your geometry is correct. And I suspect the AoA vane was at one of its stop positions. Given the phrasing it hits a stop not far beyond 35 degrees.


I can't find for sure what AoA probe was actually fitted to the AF447, but a likely candidate is a Thales C16291AA which has a catalog range of +/- 60 degrees - but this "Local Angle of Attack" gets corrected before use, so the limit is likely in the corrections/compensations.

Note this AoA probe has recently been subject to an AD to correct a manufacturing issue - excess oil which could impede motion at low temperatures. I don't know exactly what triggered this AD, the Perpignan A320 had Goodrich 0861ED probes, two of which probably froze at altitude due to water ingress during cleaning.

[Litebulbs]

Simple trigonometry: if the speed vector is at a 45 degrees angle then vertical speed is equal to horizontal speed.

I doubt that an object weighing hundreds of tonnes, moving at great speed under its own power and 10km in the air and designed to be in that environment, would end up in a simple trig equation, where vertical equaled horizontal. But it is one possibility I suppose.

[FE Hoppy]

RudderRudderRat:
During unreliable air speed whilst the crew held the wings level using constant left roll input, but with a mistaken light back pressure, it trimmed the aircraft fully nose up in response - without them realising. That's bad.

BEA:
The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs.

and
The PF made an input on the sidestick to the left and nose-up stops, which lasted about 30 seconds.

not sure where "light back pressure" comes from?

[Dublinboy]

good morning ,have to say a big thank you to all you that have made this site a must read every day its been fasinating to say the least . I wont make any contributions as im only a ppl holder and no nothing about the complexity of the the large commercial jets other than admire the people who fly them world wide every day ,my hats off to you all !
now i would like to ask a qustion that is probally been answerd already but either i missed it or didnt pick up on it.
if after a seemisly normal departure climbout and well into their cruise part of the flight with the only concern was the weather they seen on their rader the slight tuberlence they where experiening at the moments before inpact .can anyone explain why at cruise speed what ever the value is ? they redused to mach.8 to enter the moderate tuberlante airflow ,which i can understand ,but shortly after they get a unreliable airspeed indication a/p dissigages ,pilot takes over manually and stall warning goes of.. would you really believe you could be in a stall situation if you where doing cruise speed? i understand at that fl and speeds the margins for stall are really ssmall but could you believe all your airspeed just bled off like that,major up draft maybe .anyway thanks

[rudderrudderrat]

Hi FE Hoppy,

not sure where "light back pressure" comes from?

"At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law ...
The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs. The vertical speed, which had reached 7,000 ft/min, dropped to 700 ft/min and the roll varied between 12 degrees right and 10 degrees left."

He must have made some unnoticed back pressure input to climb.

[Graybeard]

What part of the wing is creating lift, and forward velocity at >40 degrees AOA? The roots probably stall below 20 Degrees, and the wing is fully stalled at a few degrees more, the tips stalling last in normal wing design. You should get a good pitch down moment while the root is stalled, and still have roll authority. Beyond that, the machine is no longer planing through the air.

Was the 107 Kts reported by the BEA really Groundspeed, i.e., horizontal velocity, or was it merely 107 Kts velocity in any direction?

Was there any evidence in the wreckage showing any forward speed at all? I believe the radome was broken, but not smashed.

Anyway, it's challenge for the synapses.

[HazelNuts39]

would you really believe you could be in a stall situation if you where doing cruise speed?The plane first traded 60% of its speed for height in going from FL350 to FL380. Then it stalled.

[Litebulbs]

The plane first traded 60% of its speed for height in going from FL350 to FL380.

Regards,
HN39

Did it? How do we know, if we are looking at invalid speed indications?

[FlexibleResponse]

History
History
One of the more interesting (to me) on-line documents relating to the history of recommendations concerning the use (or non-use) of trim during recovery from upsets in transport aircraft is a talk given by Captain William Wainwright, Chief test pilot of Airbus.

The full text is available from at least two sources (one being the NTSB).
http://www.ntsb.gov/Events/2001/AA58...its/240005.pdf
http://www.skybrary.aero/bookshelf/books/435.pdf

Here are some extracts. The omission of text in these extracts is indicated by “………”.

--------- Start of quote extracts -----------
AIRPLANE UPSET RECOVERY TRAINING AID,
By Captain William Wainwright, Airbus Industrie.

INTRODUCTION
The idea for a joint industry working group to produce an Airplane Upset Recovery Training Aid was first proposed by ATA in June 1996. ........ The end result of 2 years work is a training package including a video and a CD-ROM, giving an airplane upset recovery training aid. This package is on free issue to all of you, to use or not to use as you wish. ………..The content of the package is not my subject today, but there are a few issues of general interest which I gained from my experience as a member of the working group which I would like to talk about.

2. THE BEGINNING
…… Right from the beginning there was a conflict between the technical advice given by the manufacturers' training pilots and that expressed by those of the principal airlines already practicing upset training. They naturally considered themselves to be the experts on this subject, based on the many .hours of training that they had already conducted on a large number of pilots in their simulators. At the beginning of 1997, the Flight Test Departments were asked to come in to support their training pilots. From then on, the chief test pilots of the 3 major manufacturers became members of the working group; XXX of Boeing, YYY of McDonnell-Douglas (now Boeing - Douglas Products), and myself. But the conflict over the different opinions on aircraft handling and recovery techniques continued for a long time until we finally achieved agreement at the last meeting in January 1998. The reasons for these differences of opinion are the subject of my talk today.

3. THE DIFFERENCES
The differences of opinion were mainly concentrated in the following areas:
(a) Procedures versus general advice.
(b) Ease of training versus failure cases.
(c) Stalling.
(d) Use of rudder.
(e) Use of simulators.

It is worth saying that there was never any difference of opinion between the three test pilots on the group. Although we come from different backgrounds and have worked in different organizations with different work cultures, we always agreed on our technical advice.

4. PROCEDURES VERSUS GENERAL ADVICE
The airlines wanted simplified procedures which were common to all aircraft in their fleets and which were easy to teach and easily reproducible. This is understandable because you are all interested in having a standard product at the end of your training programmes. And this is what they already had with the Airplane Upset Recovery Training that they were already doing. For the training managers from American Airlines, Delta, and United, the only thing necessary was to give an overall industry approval to their existing programmes; they already worked, because the many pilots that had undergone training all came out of it with the same standardized reactions to the standard upsets. For them, this was the necessary proof that their training programme worked.

Where we differed was in our conviction that there was no such thing as a standard upset and our reluctance to endorse simplified procedures for recovery from an upset. We wanted a general knowledge based approach, as opposed to a rule based one. For this, after proposing some initial actions, we talk about “additional techniqlies which may be tried”. This obviously is more difficult to teach. ...........

5. EASE OF TRAINING VERSUS FAILURE CASES
The training that was already being done considered upsets as being due to momentary inattention with a fully serviceable aircraft that was in trim when it was upset. We would like to consider other cases that involve failures of control systems or human errors leaving the aircraft with insufficient control authority for easy recovery.

This of course complicates the situation, because recovering an aircraft which is in trim, possessing full control authority and normal control forces, is not the same as rocovering an aircraft with limited control available or with unusual control forces. Thus, for us, an aircraft that is out-of-trim, for whatever reason, human or mechanical failure, should be re-trimmed. Whereas the airline instructors were against the use of trim because of concerns over the possibility of a pilot overtrimming and of trim runaways which are particularly likely on some older aircraft types which are still in their fleets. We spent a lot of time discussing the use of elevator trim, and we never reached agreement. All the major US airlines were adamant on their policy to recover first using “primary controls” which excluded any reference to trimming. Again, a compromise was necessary. What we have done is to talk about using trim if a sustained column force is required to obtain the desired response whilst mentioning that care must be used to avoid using too much trim. And, the use of trim is not mentioned in the simplified lists of actions to be taken.

6. STALLING
Another aspect that was 'being ignored in the existing training was the stall. By this I mean the difference between being fully stalled and the approach to the stall. In training, you do an approach to the stall with a recovery from stick shaker, which is often done by applying full thrust and maintaining existing pitch attitude in order to recover with minimum loss of height. Height cannot be maintained if an aircraft is actually stalled and should be of secondary importance. .......

There is a world of difference between being just before, or even just at, the stall, and going dynamically well into it. The training being given in the airlines at the time to recover from excessive nose-up pitch attitudes emphasised rolling rapidly towards 90" of bank. This is fun to do, and it was not surprising to find that most of the instructors doing the training were ex-fighter pilots who had spent a lot of time performing such manoeuvres in another life. The training was being done in the same way, with an aircraft starting in trim with a lot of energy and recovering while it still had some. However, the technique being taught only works if the aircraft is not stalled. ……..
If the airplane is stalled, it is imperative to first recover from the stalled condition before initiating the upset recovery technique. Do not confuse an approach to stall and a full stall. An approach to stall is controlled flight. An airplane that is stalled is out of control and must be recovered.
A stall is characterised by any, or a combination of the following:
--- Buffeting, which could be heavy at times.
--- A lack of pitch authority.
--- A lack of roll control.
--- Inability to arrest descent rate.
To recover from a stall, the angle of attack must be reduced below the stalling angle. Apply nose down pitch control and maintain it until stall recovery. Under certain conditions with under-wing mounted engines, it may be necessary to reduce thrust to prevent !he angle of attack from continuing to increase. Remember, in an upset situation. If the airplane is stalled, It is first necessary to recover from the stall before initiating upset recovery techniques. This is something that we are well aware of in testing, but it was either being totally ignored, or misunderstood. I consider the inclusion of this note to be one of our most important contributions.

8. USE OF SIMULATORS
We manufacturers were very concerned over the types of manoeuvres being flown in simulators and the conclusions that were being drawn from them. Simulators, like any computer system, are only as good as the data that goes into them. That means the data package that is given to the simulator manufacturer. And we test pilots do not deliberately lose control of our aircraft just to get data for the simulator. …………..

The complete data package includes a part that is drawn from actual flight tests, a part that uses wind tunnel data, and the rest which is pure extrapolation. If should be obvious that conclusions about aircraft behaviour can only be drawn from the parts of the flight envelope that are based on hard data. This in fact means being not far from the centre of the flight envelope; the part that is used in normal service. It does not cover the edges of the envelope. I should also add that most of the data actually collected in flight is from quasi-static manoeuvres. Thus, dynamic manoeuvring is not very well represented. …………

In other words, you have reasonable cover up to quite high sideslips and quite high AOAs, but not at the same time. Furthermore, the matching between aircraft stalling tests and the simulator concentrates mainly on the longitudinal axis. This means that the simulator model is able to correctly reproduce the stalling speeds and the pitching behaviour, but fidelity is not ensured for rolling efficiency (based on a sirrpfified model of wind tunnel data) or for possible asymmetric stalling of Ihe wings. ......

In fact, this is a perfectly adequate coverage to conduct all normal training needs. But it is insufficient to evaluate recovery techniques from loss of control incidents. Whereas, the training managers were all in the habit of demonstrating the handling characteristics beyond the stall; often telling their trainees that the rudder is far more effective than aileron and induces less drag and has no vices In short, they were developing handling techniques from simulators that were outside their guaranteed domain. Simulators can be used for upset training, but the training should be confined to the normal flight envelope; For example, training should stop at the stall warning. They are "virtual" aircraft and they should not be used to develop techniques at the edges of the flight envelope. This is work for test pilots and flight test engineers using their knowledge gained from flight testing the "real" aircraft.
--------- End of quote extracts -----------

Picky Perkins,

Brilliant quote from Bill Wainwright! This is right on the money with regards this accident.

It deserves to be re-quoted in full, so be it...

[FE Hoppy]

Hi Rudder Rudder Rat (I remember it well!)

"At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law ...
The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs. The vertical speed, which had reached 7,000 ft/min, dropped to 700 ft/min and the roll varied between 12 degrees right and 10 degrees left."

He must have made some unnoticed back pressure input to climb.

I can't help thinking that to pitch up from cruise attitude to "beyond 10°" without increasing thrust would take more than a "light" back pressure.

[FE Hoppy]

Litebulbs:
Did it? How do we know, if we are looking at invalid speed indications?

We know where he started, we know his mass, we know that there is no increase in thrust reported and we know where he ended. So unless there was a large input of energy from an external source we can deduce how much energy was used in getting from 350 to 380.

[DozyWannabe]

Surely you know that that would run counter to all AB philosophy of 'protecting' the machine? The software know best, you, the pilot, do not need to know.:ugh:

BOAC, did you take a grumpy pill this morning?

A couple of honest questions. Firstly, did you read what I wrote yesterday re: the systems design? It's there to assist the pilot to do his or her job, not to "protect" the aircraft from bad piloting as such. Secondly, as I asked on the other thread, if Airbus thought that pilots didn't "need to know", then why would they publish an article saying that they think manual flying skills at airlines have been allowed to deteriorate too far?

The Alternate modes are there because the design brief called for them. I could try to dig up more info on that, but does it really matter?

[Litebulbs]

Litebulbs:


We know where he started, we know his mass, we know that there is no increase in thrust reported and we know where he ended. So unless there was a large input of energy from an external source we can deduce how much energy was used in getting from 350 to 380.

Absolutely agree. What happening outside the airframe could give that sort of energy and would appear by stick position, to be countered by the aircraft?

At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law ...
The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs. The vertical speed, which had reached 7,000 ft/min, dropped to 700 ft/min and the roll varied between 12 degrees right and 10 degrees left.

[HazelNuts39]

Right from the beginning there was a conflict between the technical advice given by the manufacturers' training pilots and that expressed by those of the principal airlines already practicing upset training.I wonder if the AoA indicator could be in the same tension field?

[FE Hoppy]

Litebulbs:
Absolutely agree. What happening outside the airframe could give that sort of energy and would appear by stick position, to be countered by the aircraft?


I think your quote was a little selective. This puts a different slant on it:
From 2 h 10 min 05, the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row. The recorded parameters show a sharp fall from about 275 kt to 60 kt in the speed displayed on the left primary flight display (PFD), then a few moments later in the speed displayed on the integrated standby instrument system (ISIS).
At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law [...]".
The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs. The vertical speed, which had reached 7,000 ft/min, dropped to 700 ft/min and the roll varied between 12 degrees right and 10 degrees left. The speed displayed on the left side increased sharply to 215 kt (Mach 0.68). The airplane was then at an altitude of about 37,500 ft and the recorded angle of attack was around 4 degrees.

The climb comes after the first nose up input and rate reduces after the nose down input.

I'm not excluding external forces but we have everything required for the climb without them.

[HazelNuts39]

I'm not excluding external forces but we have everything required for the climb without them.Agreed, except that 'external forces' would have changed the total energy and can be excluded on that basis.

[ihg]

Here's another hare to start running. From Der Spiegel, I believe:

"Just over a year ago, Hüttig recreated the Air France crash in a flight simulator. In the course of the exercise, Hüttig noticed a strange anomaly in the plane's reaction once it goes into a stall. The trimmable horizontal stabilizer, a flap instrumental in keeping the plane on an even keel, automatically adjusted to push the nose of the plane skyward. Hüttig, a former Airbus pilot himself, and other pilots present for the test were unable to push the nose of the airplane down and thereby escape the stall.
When the BEA released its preliminary report last Friday, Hüttig immediately zeroed in on data relating to the trimmable horizontal stabilizer. During the final minutes of flight AF 447 as it plunged toward the Atlantic, the flap moved from a 3 degree deflection to a 13 degree deflection, almost the maximum possible. "The phenomenon is startlingly similar," he told SPIEGEL......
BOAC, independent if there is some real basis behind Hüttig's "findings" or not,
this guy and his collegue professor and lawyer Elmar Giemulla have an agenda.

And this agenda is MONEY.

Hüttig works in support of Giemulla, who represents the interests and claims of the relatives of the German victims of the accident.
Already in May 2010, Giemulla publicly announced that he files a lawsuit against... guess who? not Airbus, not Air France, but the French government (to be turned in in July 2010, no idea if it ever actually happened). Reasoning: The French government is shareholder of AF and Airbus and this has failed its responsibility to properly control the actions and processes of the respective companies.

Well, in the best tradition of American lawyer, allways sue those who really have the money and who can be made pay most likely, no matter whose fault it really was.

Already in November 2009, Guiemulla claimed, AF would bear the main responsibility for the crash. Well who needs to find FDR on the bottom of the ocean and perform a thorough accident investigation? BEA should simply ask the lawyer, they know it all.
Also already in Nov 2009, Giemulla stated that he expects to achieve a 6digit number of compensation for each victim (i.e. >1 million Euro).

Well, whatever these guy tout as "findings", I would recomment to handle with extreme care. They have an unambiguous interest in who has to to blamed.

[alf5071h]

Dublinboy, et al, re #1221. Look back at #883 (para 3) as to a possible reason why the aircraft climbed, thus disturbing level flight and stable trim conditions:- http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-23.html#post6485314

[Lonewolf_50]

HN39, the energy tradeoff (~60%) takes us back to instrument scan.

How would PF NOT know he's climbing? How would PNF not see the climb and not comment. (CVR data/info would be handy here ... ) Are there two sets of eyes locked on airspeed indications with other parameters dropping one by one from scan? What CVR recordings match up to the fwd stick/reduction in climb rate? There is much missing here in terms of task management leading up to what appears to have become a task overload.

Here is something I know happened in the 80's. Helicopter crew in Persian Gulf, night, a few hundred feet over water, both pilots concentrate on the tactical display because something of interest had arisen. (Note, the PF and PNF roles had been lost. Two sets of eyes were on a display that is not the flight instruments, zero sets of eyes were on flying instruments).

For one reason or another, alt hold was either not on, or deselected. The helicopter descended toward the water. The RAWS tone (radar altitude warning) went off, and PF added power. Helicopter skipped off the water, kept flying, and was returned to its ship. That event was a few fractions of a second away from aircraft and crew in the water. The incident became boilerplate CRM and task management fodder for some years after that.

Which tasks and which stimuli attracted the most attention of the AF 447 crew? This is a significant unknown.

[CogSim]

I doubt that an object weighing hundreds of tonnes, moving at great speed under its own power and 10km in the air and designed to be in that environment, would end up in a simple trig equation, where vertical equaled horizontal. But it is one possibility I suppose.

This a/c seems to have somehow remained stalled from FL380 to at least FL100 which in itself is quite a feat. But, if I were to put my money on it, I'd say the Pi/4 angle at impact for a machine with the wings and power of A330 makes it an extraordinary coincidence, if it was still flying in the conventional sense. With the very limited data we have, the descent profile is suspiciously close to ballistic with some lateral control.

[Welsh Wingman]

Does anyone know where I can find on the web a copy of the NTSB report on NW6231 way back in the 1970s? Much obliged.

[Litebulbs]

Are you basing the loss of speed on what was indicated, because isn't that indicated speed under question, due to icing of the pitots?

[RegDep]

http://libraryonline.erau.edu/online-full-text/ntsb/aircraft-accident-reports/AAR75-13.pdf for Welsh Wingman

[BOAC]

BOAC, did you take a grumpy pill this morning? - no bigger a pill than usual A couple of honest questions. Firstly, did you read what I wrote yesterday re: the systems design? It's there to assist the pilot to do his or her job, not to "protect" the aircraft from bad piloting as such. There I disagree - it IS there to protect from 'bad piloting as such' and it does it very well in normal circumstances - things like excessive pitch, too high an AoA, too much 'g' etc etc.
Secondly, as I asked on the other thread, if Airbus thought that pilots didn't "need to know", then why would they publish an article saying that they think manual flying skills at airlines have been allowed to deteriorate too far? - you need to remember that normal 'manual flying' in an Airbus is still 'protected' by the system. Thus they do NOT need to know the limits of safe flying, even manually, as the aircraft controls those.
The Alternate modes are there because the design brief called for them. I could try to dig up more info on that, but does it really matter? - no. That was EXACTLY my point!

[FE Hoppy]

Welsh Wingman:
Flugunfall 01 DEC 1974 einer Boeing 727-251 N274US - Stony Point, NY (http://aviation-safety.net/database/record.php?id=19741201-1&lang=de)

Litebulbs:
Not sure what you're asking? The indicated airspeed whether accurate or not isn't the issue in determining the energy state of the aircraft. We know what the airspeed was before the incident. We know that the crew are not reported to have added thrust and that the AT was disconnected. You can't climb for free so the energy came from speed. They stopped climbing when they were at the ceiling for their thrust setting at the alpha they were commanding. Note that when TOGA was selected they were able to climb a further 500ft. In this case they added energy to the equation.

[Tailspin Turtle]

What part of the wing is creating lift, and forward velocity at >40 degrees AOA? The roots probably stall below 20 Degrees, and the wing is fully stalled at a few degrees more, the tips stalling last in normal wing design. You should get a good pitch down moment while the root is stalled, and still have roll authority. Beyond that, the machine is no longer planing through the air.

Note that skydivers, before they open their parachutes, have a glide ratio at a very high angle of attack, just not a very good one. With a fabric "wing," the glide ratio improves. Click HERE for an example.

Similarly, the wing is still providing "lift" beyond the stalling angle of attack, just less and less of what it was before, and more and more drag. The airplane should pitch down at stall because the center of gravity is ahead of the center of lift but in this case, the center of gravity may not have been been very far ahead of the center of lift and you've obviously got engine thrust, an almost fully nose-up trimmed horizontal stabilizer (which is probably sized to keep the cg range as wide as possible), and nose-up elevator creating enough nose-up pitching moment to offset any nose-down moment. I am surprised that there was still enough roll control authority at that angle of attack to keep the wings more or less level.

[FE Hoppy]

Tailspin Turtle wrote:
The airplane should pitch down at stall because the center of gravity is ahead of the center of lift

Not really?

CoG could be some way behind the "centre of lift". In this case the CoG was at 29% MAC. The "centre of lift" would generally be at 25%.

[Lonewolf_50]

AOA vane has physical stops. It has to be 35-40 degrees, so greater than 40 degrees AOA can only be calculated from the IRU, which data has apparently not been released, and the BEA are quoting AOA only from the vanes. I'm betting real AOA at the end was 100-120 degrees.

Graybeard, to get the AoA value you suggest, would not the aircraft have to be moving backwards?

See the diagram here.

Angle of Attack Indicator (http://www.navyair.com/Angle%20of%20Attack%20Indicator.htm)

If you move (orange) line (marked number three) down, you increase the the angle. To get to the value you assert, the orange line, resultant relative wind, would have to be coming from behind the aircraft's nose, behind and below the leading edge of the wing. That would need for the plane to be dropping not just straight down, but straight down and roughly moving in the direction (with nose up 16 degrees) that the tail was pointing. If it were doing that (and I doubt it was) the ailerons would not provide lift. The flight path described (see takata's picture some pages back) by the data BEA provides, indicates a long, wide, right turn (almost a teardrop) from apex of climb to impact with the water. Nowhere does the BEA report indicate the rapid change of heading associated with a spin.

So if it didn't spin, but was stalled, and was in a rate of turn that described the track over the ground from that reconstructed picture, the aircraft was moving in the direction that the nose, not the tail, was pointing. More to the point, your estimate would require the aircraft (whose ground speed was reported as 107 knots) experience a massive microburst of airflow to hold that AoA (relative wind from behind) and 107 knots forward.

Your AoA estimate there does not fit what has been reported.

Can you sketch out why you come up with that estimate, or were you tossing that against the wall to see if it would stick?

[Litebulbs]

I am confused, that's all. At 2:10:05 and M0.8 there was a L Up input with a warning and a massive drop off in IAS. At 2:10:16 a climb started, increased to 7000fpm then reduced to 700fpm with an increase in ALT of 2500ft by 2:10:50 at M0.68.

So in 34 seconds at 7000fpm you could achieve a 4000ft increase in ALT. But surely you have to start the climb and then reduce it to 700fpm too, all within 34 seconds, whilst still having a forward speed of M0.68 and all from all from energy contained within the airframe.

[grity]

they think manual flying skills at airlines have been allowed to deteriorate too far....after creating the "zoom-boom scenario" up to FL400+ to bring down the kinetic energie of 205 t with 240 m/s to an flightlevel zero without a highspeedchrash.... within 4-5 min... within less than 10 miles

we all thought: yes it seems physical possible, BUT it can not be because no pilot will pull in this situation....

and now we know the way, it need only a pull at the elevator a bit over some time and the right or wrong (too-loose-)lav for the follow of the trim to the max position and with a 270 deg segment of circle a climb to FL380 is enough to bring the kinetic energie to FL zero... BUT by all RAZORs I can not believe that the PF has pulled up over 3 min with his hand, pulled with all skills he had in his hands

you have more sensors in one hand than all airplanes together have in all ther highly sophisticated technic,

even if the PF sits his first day on the left side and had used the stick only with his right hand on the rhight side before, he will not pull so long..... no no no

so are we shure we can roll out all other possibility reasons for the up move of the trim?

icing AoA vane ???
the g-sensore
is the trim lav absolutly save, in all moments during the disconnect of the AP while changing the lavs???
something else.......I do not know

if an actuator like the auto-trim has a faulty circuit it either stops at the last position or it run to the end common with low energy an actuator can run to the end(my first RC-modell crashed in first flight, the elevator moved full down, I just plump forgott to recharge the akku before flight....)I also did not understand the climb of the A340 after disconect the AP, they say nothing over the trim, the say the flightpath followed a g-protection in this case, the path will oscillate in altitude, my feeling is even this jet was nearly before stalling and the protection was the PF ???

if the g-protection work over the elevator will the trim than beginn to follow also?

work the g-protection together with the airspeed? or the AoA?

[Lazerdog]

RegDep.... Things haven't changed much since the '70's have they? As I posted several dozen pages back, an aircraft can "feel" pretty normal in a stall on a dark and bumpy night. You have to look for clues like the altimeter unreeling to know what's happening if airspeed, FPV, and AOA are suspect or missing. Thanks for posting the report. Hopefully the world's instructor pilots are reading.....

[FE Hoppy]

So in 34 seconds at 7000fpm you could achieve a 4000ft increase in ALT. But surely you have to start the climb and then reduce it to 700fpm too, all within 34 seconds, whilst still having a forward speed of M0.68 and all from all from energy contained within the airframe.

Well the pitch input was at 05 and the climb commenced at 16. The peak value was 7000fpm but the mean was about 1400fpm. If we are to believe the the quoted speeds they lost 60kts in this manoeuvre and ended with the same thrust setting and 4°alpha.

How about this scenario:
PF makes his correction for roll and doesn't notice the rate of climb or is confused by the stall warning. When he notices the 7000fpm he corrects with nose down and levels at 375 all without adding thrust. He's now at 4°alpha but having not added thrust his speed is reducing which induces the second stall warning. Now he adds the thrust and pulls up. The aircraft doesn't have much more thrust to give and his alpha is increasing all the time while the speed is reducing. We know that the isis speed comes back at 2:11:06 (15 seconds later ) and shows 185 which matches the PFD.

Doesn't appear unreasonable and doesn't require any external energy input.