AF447 Thread No. 3
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Sorry for the silly questions: in ALT, the sidestick controls load factor demand, correct? Once the a/c is stalled, that load factor demand cannot be met. In fact, g would have been <1 at some point. What happens then if the sidestick is in its neutral position? In particular, would the autotrim be active?
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Readers Digest Condensed Version - Rush to Pilot Error
The post volume is definitely up since Friday's release, but I don't know that we can say the same for the post quality. We were all hoping for "the answer" to be released on Friday, and I think a lot of people, especially some of the general media seem to feel it was, and that the answer was pilot error.
What we got from the BEA was basically a condensed version of what happened, and it leaves with a pilot taking what appears to be an unexplained action, 30s of pitch up.
Coming from a technical and software background (machinbird and others can probably tell from where) one might think I would be quick to jump on the pilot error bandwagon, but I am not.
If we look at this from the standpoint of Input --> Decision --> Output we have, I feel, only partial insight to what the inputs to the pilots were, we don't know, from what was given so far, what the decision making process was, and we have at least some of the outputs, the pitch, roll, throttle commands but not a real understanding as to why those choices were made when they were made.
Hopefully when a more complete release of the CVR and DFDR information is made we will gain greater insight as to the decision making process and "why" of the pilot actions. I find it hard to believe that if they appear counter intuitive that we are not missing parts of the picture either from the brief release, or limitations to what data is collected in the complete record.
These pilots had a very vested interest in solving the problem they were presented, I strongly suspect there was a lot more discussion and information than we are currently being given. Though the BEA may have been wanting to help stem the amount of leaked information, they may have added to the amount of misinterpretation, or rushed judgement.
I also hope the moderators will ensure that several of our new posters who share a common viewpoint do not originate from a single IP address.
What we got from the BEA was basically a condensed version of what happened, and it leaves with a pilot taking what appears to be an unexplained action, 30s of pitch up.
Coming from a technical and software background (machinbird and others can probably tell from where) one might think I would be quick to jump on the pilot error bandwagon, but I am not.
If we look at this from the standpoint of Input --> Decision --> Output we have, I feel, only partial insight to what the inputs to the pilots were, we don't know, from what was given so far, what the decision making process was, and we have at least some of the outputs, the pitch, roll, throttle commands but not a real understanding as to why those choices were made when they were made.
Hopefully when a more complete release of the CVR and DFDR information is made we will gain greater insight as to the decision making process and "why" of the pilot actions. I find it hard to believe that if they appear counter intuitive that we are not missing parts of the picture either from the brief release, or limitations to what data is collected in the complete record.
These pilots had a very vested interest in solving the problem they were presented, I strongly suspect there was a lot more discussion and information than we are currently being given. Though the BEA may have been wanting to help stem the amount of leaked information, they may have added to the amount of misinterpretation, or rushed judgement.
I also hope the moderators will ensure that several of our new posters who share a common viewpoint do not originate from a single IP address.
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Caygil asked: "Would it be out of question to create an automation graceful degradation, which:.."
There is a patent filed, since the accident, on just this idea.
The more I think about it the more I suspect that the plane could fly perfectly well using only GPS and inertial data if it's looking to maintain altitude, attitude, and speed. Abnormal conditions would be indicated by the precursor conditions to either stall or mach buffet. Actual stall would be indicated by altitude loss. So for modest periods of time the plane could probably do very well on such data as it has. I'm not sure retrofitting this "learning" software into the ancient (in computer years) computers aboard an A330. But it certainly could be incorporated into new designs.
There is a patent filed, since the accident, on just this idea.
The more I think about it the more I suspect that the plane could fly perfectly well using only GPS and inertial data if it's looking to maintain altitude, attitude, and speed. Abnormal conditions would be indicated by the precursor conditions to either stall or mach buffet. Actual stall would be indicated by altitude loss. So for modest periods of time the plane could probably do very well on such data as it has. I'm not sure retrofitting this "learning" software into the ancient (in computer years) computers aboard an A330. But it certainly could be incorporated into new designs.
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Originally Posted by JD-EE
I am also reading this as the aircraft presuming 60kts is an obvious stall so let's warn the pilot he's about to stall. (There being no real unique stall warning.) That's the moment the fit hit the shan.
So for me there is no reason to doubt that even the first stall warnings were correct.
Originally Posted by JD-EE
Is this because the stall warning is taught as "the plane cannot stall, this is a warning it might (contradictory here but a paraphrase of what I've read here) stall so pull up and push throttles forward some to compensate."...So as I see it, based on messages here, the pilots reacted to training and pulled up.
...pull up? Excuse me. I have no idea where you get that from,,,,but you will hardly find anyone in the world proposing that as 'stall procedures', except those with suicidal tendencies...
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If I am misreading some recent posts, I apologize, but there seems to be some confusion about stall warning and airspeed. The sudden drop in indicated airspeed was due to ice particles blocking the pitots, not due to a real speed reduction. Stall warning begins when the AoA exceeds approx. 4 degrees, and that threshold was exceeded at several times. AoA reached 16 degrees at 38000 ft, indicating that the airplane was definitely stalled at that point.
Stall warning, followed a few seconds later by uncommanded left/right rolling motions probably accompanied by heavy buffet is usually accepted as an indication of "you are now stalled".
Stall warning, followed a few seconds later by uncommanded left/right rolling motions probably accompanied by heavy buffet is usually accepted as an indication of "you are now stalled".
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Until a fault tolerant method is developed for obtaining airdata, I hope UAS drills become far more comprehensive in the sim. For three rated pilots to miss the recovery is shocking, assuming BEA isn't leaving out some important tidbits.
Oh, and patch the bugs in the stall warning system for low airspeeds and/or AoA... No doubt that design "feature" should be reclassified as a bug.
Lastly, the man machine interface really needs some review regarding sidestick, thrust lever, and trim positions. When you are 3 minutes from doom you should be given enough information as quickly and comprehendible as possible to take over from Otto when he can't figure it out.
Oh, and patch the bugs in the stall warning system for low airspeeds and/or AoA... No doubt that design "feature" should be reclassified as a bug.
Lastly, the man machine interface really needs some review regarding sidestick, thrust lever, and trim positions. When you are 3 minutes from doom you should be given enough information as quickly and comprehendible as possible to take over from Otto when he can't figure it out.
Surely in a spiral dive you would have increasing G if you pulled backstick which you could sense. Can't see the confusion myself, certainly not for 4 min's.
In this case we see that Attitude+Power was not obtaining the Performance one would normally expect.
The crew seem not to have realised they were in the stall regime while all us of in our armchairs are at a loss to understand why they did not.
I have seen somebody in a steam gauge sim with white on black AH invert the ac at 16000' and fail to realise what he had done until after he "hit" the ground. Fixation can take over, and deafen you to the guy yelling "roll left" directly in your right ear.
Here it seems the entire crew were aware they were on the way down without knowing why or anybody offering any ideas on how to change the situation for the better.
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garage years
many thanks for link on pitch and AOA. as a SLF myself i have followed the AF447 thread from the beginning on PPRUNE. may i ask what is TOGA and the ISIS display. thanks
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"But it does appear, if my understanding of the Airbus FBW system (gleaned mostly from these threads) is correct, that the aircraft would have continued in straight and level (and unstalled) flight absent the left nose-up input by the PF."
Great question, I trust a knowledgeble poster will answer for us.
Thanks in advance
Great question, I trust a knowledgeble poster will answer for us.
Thanks in advance
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Here it seems the entire crew were aware they were on the way down without knowing why or anybody offering any ideas on how to change the situation for the better.
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OPENDOOR, I figure good sense disagrees with your rather broad statement. The inertial system can tell if the plane has actually decelerated or accelerated by over 200 kts or even 50kts and the mother of all tail winds overtook the plane. So there is a valid software check on the stall warning.
Furthermore, AI seems to think there is enough information in the inertial and GPS systems to keep the plane flying while the pitots recover. The plane has a tremendous amount of inertia. So one minute or less of simple pitch and altitude with comparison between inertial/GPS data on ground speed can diagnose whether they are in a large wind or not. If they are in a savage tail wind they will cover more ground than they should for the past ground speed. The difference is the speed of the tail wind. The same fits for any other strong wind. If you are not deviating from the previous course with no control changes then your airspeed cannot have changed.
It appears on a closer look that my naive question from a couple years ago has an even better answer than I'd thought at the time. It may give a bumpy ride for a couple minutes. But it will keep the plane going very nicely. It can tell you if you did hit a wind, what you need to do to correct for it. And the inertial system should be able to tell you quite rapidly what is going on.
However, the GPS alone is indeed useless. It's lag is too large. It can be cozened into giving you real velocity figures. The accuracy may not be as much as you like. (Three GPS antennas and differential phase tracking GPS can give you plane attitude, on large planes, fairly accurately, too.) GPS's main fault is that it tells you where you were not necessarily where you are. That's why you have Kalman filters and inertial navigation systems in the picture.
(And, yes, bienville, I do have a half a notion of what I am talking about with GPS.)
Furthermore, AI seems to think there is enough information in the inertial and GPS systems to keep the plane flying while the pitots recover. The plane has a tremendous amount of inertia. So one minute or less of simple pitch and altitude with comparison between inertial/GPS data on ground speed can diagnose whether they are in a large wind or not. If they are in a savage tail wind they will cover more ground than they should for the past ground speed. The difference is the speed of the tail wind. The same fits for any other strong wind. If you are not deviating from the previous course with no control changes then your airspeed cannot have changed.
It appears on a closer look that my naive question from a couple years ago has an even better answer than I'd thought at the time. It may give a bumpy ride for a couple minutes. But it will keep the plane going very nicely. It can tell you if you did hit a wind, what you need to do to correct for it. And the inertial system should be able to tell you quite rapidly what is going on.
However, the GPS alone is indeed useless. It's lag is too large. It can be cozened into giving you real velocity figures. The accuracy may not be as much as you like. (Three GPS antennas and differential phase tracking GPS can give you plane attitude, on large planes, fairly accurately, too.) GPS's main fault is that it tells you where you were not necessarily where you are. That's why you have Kalman filters and inertial navigation systems in the picture.
(And, yes, bienville, I do have a half a notion of what I am talking about with GPS.)
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GY, maybe this answers some questions?
This is the important part: "The PF made nose-down control inputs and alternately left and right roll inputs."
The PF did indeed stick the nose down. It didn't work.
At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law […]". Note 1: The angle of attack is the angle between the airflow and longitudinal axis of the airplane. This information is not presented to pilots.
Note 2 : In alternate or direct law, the angle-of-attack protections are no longer available but a stall warning is triggered when the greatest of the valid angle-of-attack values exceeds a certain threshold.
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
Note 2 : In alternate or direct law, the angle-of-attack protections are no longer available but a stall warning is triggered when the greatest of the valid angle-of-attack values exceeds a certain threshold.
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 PF did indeed stick the nose down. It didn't work.
Inexplixable Happens
An acquaintance of mine was once making a routine test flight in a helicopter under development. In the brief, he had been reminded by engineering that high-inertia rotor blades were installed (not part of the test) and therefore not to let the rotor rpm get too high. During the flight, which involved shutting down an engine, he was presented with an unanticipated failure/condition with the rotor tachometer going to and freezing at an overspeed indication. He raised the collective to get the rpm down and fixated on the indicated rpm. He persisted in holding the collective up even though it wasn't producing a change in the indicated rpm and the rotor had slowed well beyond the point that he should have first recognized that it was below normal. (Apocryphally, to the point where he should have been able to see the individual blades instead of a disc...)
Presumably Airbus and Air France are putting line pilots into a simulator and exposing them to the same instrument indications and aural warnings to see what they do.
My understanding is that the side sticks are not connected and have limited range of motion so the pilot not flying and the pilot(s) observing have no idea what the control inputs of the pilot flying are. If the pilot flying were doing the inexplicable, they wouldn't be able to tell?
Presumably Airbus and Air France are putting line pilots into a simulator and exposing them to the same instrument indications and aural warnings to see what they do.
My understanding is that the side sticks are not connected and have limited range of motion so the pilot not flying and the pilot(s) observing have no idea what the control inputs of the pilot flying are. If the pilot flying were doing the inexplicable, they wouldn't be able to tell?
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many thanks for link on pitch and AOA. as a SLF myself i have followed the AF447 thread from the beginning on PPRUNE. may i ask what is TOGA and the ISIS display. thank
TOGA = Take-off Go-Around (thrust setting)
ISIS= integrated stand-by instrument system
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Sir John:
One point bothers me. Putting aside the possibility that the crew was simply overwhelmed by multiple sensory inputs and just could not think straight (and I suspect that we all have been in such a situation from time to time in the box), how is it that the observation of
(a) a reasonably level or nose up attitude plus
(b) low IAS plus
(c) a shedload of ROD
doesn't immediately equal the mental deduction of stall ?
(a) a reasonably level or nose up attitude plus
(b) low IAS plus
(c) a shedload of ROD
doesn't immediately equal the mental deduction of stall ?
Last edited by vapilot2004; 28th May 2011 at 20:18.
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Post #237 (Svarin) and post #260 (mm43) are both recommended reading.
Re #237 : Svarin's speculation has a certain uncomfortable ring of truth. Protection mechanisms can be a doubled edged, and can often bite when one of those 'unknown unknowns' comes out of the woodwork. Post #4 in "Not good in an ETOPS/EROPS TWIN" is an excellent description of a similar conflict between man and machine.
http://www.pprune.org/tech-log/43214...rops-twin.html
Re #237 : Svarin's speculation has a certain uncomfortable ring of truth. Protection mechanisms can be a doubled edged, and can often bite when one of those 'unknown unknowns' comes out of the woodwork. Post #4 in "Not good in an ETOPS/EROPS TWIN" is an excellent description of a similar conflict between man and machine.
http://www.pprune.org/tech-log/43214...rops-twin.html
It falls under the general category of "deadly embrace," where neither of the two control entities has both the information and the ability to resolve the problem.
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ihg, there is a difference between "a stall is coming" and "you are stalled". When near the ground do you want to nose down BEFORE the stall?
They weren't near the ground. But were they trained for high altitude actual stalls?
They weren't near the ground. But were they trained for high altitude actual stalls?
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JD-EE
The nose was never down! Have a look at post #260.
I notice a number of regular posters are quiet, which is to be expected.
BJ-ENG
Thanks for noticing!
The nose was never down! Have a look at post #260.
I notice a number of regular posters are quiet, which is to be expected.
BJ-ENG
Thanks for noticing!