AF 447 Thread No. 9
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Quote:
Originally Posted by RetiredF4
So you agree now, that the NU trim should have been designed to stop like it does in the A 320. That is a big advance in this discussion.
I neither agree nor disagree - I don't have the evidence to support a case for one design being better or worse than the other.
Originally Posted by RetiredF4
So you agree now, that the NU trim should have been designed to stop like it does in the A 320. That is a big advance in this discussion.
I neither agree nor disagree - I don't have the evidence to support a case for one design being better or worse than the other.
Nevertheless ... even without trim (neutral) .. just give ( continually ) up orders (like the AF447 pilot had done) with the elevators (supposed they have enough authority) will finally end up in a stall situation
Last edited by jcjeant; 28th Jul 2012 at 19:44.
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Originally Posted by DozyWannabe
however the THS was in the position it was because the pilot had held the stick back for so long
On the A320 the autotrim stops (at about 6 degrees nose up if I recall correctly)
Where is your official documentation stating that the A320 autotrim stops at 3 degrees ?
Accident reports tend to summarize rather than detail every experiment performed to the Nth degree - otherwise they'd routinely run into thousands of pages.
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Remember, you used ONE A320 SIMULATOR, not a A320.
Where is your official documentation stating that the A320 autotrim stops at 3 degrees ?
Where is your official documentation stating that the A320 autotrim stops at 3 degrees ?
It was full nose up .. and was not returned (manually) when plane got in direct law
I can be wrong ...
EDITED :
Stalled AF447 did not switch to abnormal attitude law
There has been no indication that the aircraft switched into any other control law, other than alternate, during the accident - suggesting that auto-trim was available throughout the descent.
Failure to realise a need for manual re-trim was central to the loss of an Airbus A320 over the Mediterranean Sea about six months before the AF447 crash.
The auto-trim had adjusted the horizontal stabiliser fully nose-up but, during a flight envelope test involving near-stall, the aircraft switched control laws and inhibited the auto-trim.
Without manual re-trimming, the aircraft pitched up sharply as the crew applied maximum thrust. It stalled and the crew lost control.
In its conclusions over the accident the BEA highlighted the rarity of the need to trim manually, which created a "habit" of having auto-trim available made it "difficult to return to flying with manual trimming".
"One of the only circumstances in which a pilot can be confronted with the manual utilisation of the trim wheel is during simulator training," it said. "However, in this case, the exercises generally start in stabilised situations."
In the wake of the A320 accident, near Perpignan in November 2008, the BEA recommended that safety regulators and manufacturers work to improve training and techniques for approach-to-stall situations, to ensure control of an aircraft in the pitch axis.
Failure to realise a need for manual re-trim was central to the loss of an Airbus A320 over the Mediterranean Sea about six months before the AF447 crash.
The auto-trim had adjusted the horizontal stabiliser fully nose-up but, during a flight envelope test involving near-stall, the aircraft switched control laws and inhibited the auto-trim.
Without manual re-trimming, the aircraft pitched up sharply as the crew applied maximum thrust. It stalled and the crew lost control.
In its conclusions over the accident the BEA highlighted the rarity of the need to trim manually, which created a "habit" of having auto-trim available made it "difficult to return to flying with manual trimming".
"One of the only circumstances in which a pilot can be confronted with the manual utilisation of the trim wheel is during simulator training," it said. "However, in this case, the exercises generally start in stabilised situations."
In the wake of the A320 accident, near Perpignan in November 2008, the BEA recommended that safety regulators and manufacturers work to improve training and techniques for approach-to-stall situations, to ensure control of an aircraft in the pitch axis.
Last edited by jcjeant; 28th Jul 2012 at 21:42.
Originally Posted by BOAC
I understood from the report that they were in fact able to maintain a high nose attitude in pitch with side-stick/THS and/or lower the nose occasionally with side stick? Is that not 'control', even if 'up' was the wrong 'control'? Am I wrong?
If stick is pressed against the left stop and aeroplane rolls gently to the right, you are out of control.
If stick is pulled against the rear stop and nose is just bobbing around, you are out of control.
Father of William Langewiesche wrote about the unsavoury fate of the pilots that did not understand that their inability to get the nose up was a consequence of busting the lift limit so they were pulling hard on their sticks and kept their aeroplanes stalled until ground impact delivered coup de grace. His book was first published sixty eight years ago. Seems that some of airfolks out there missed this very important lesson.
Originally Posted by rudderrudderrat
I can't imagine how you were trained to recover from a stall warning without a briefing
Originally Posted by DozyWannabe
I think it's the only large US-made airliner with a T-tail - and thus susceptible to the full-blown deep stall phenomenon.
Originally Posted by roullisholandais
but it seems that BEA could not do the best to clarify that lack
Originally Posted by Carjockey
I also remember the days when the Captain used to walk through the aircraft, and a very reassuring thing it was too.
Originally Posted by Lyman
My proposal is that the THS prevented a STALL, allowing entry into what can best be described as a MUSH.... Whatever you call it, it bore no resemblance to a normal STALL.
Originally Posted by jcjeant
Normally (at least I hope) legal experts appointed by the judge hearing the case must also be in possession of all these evidences.
Originally Posted by Lyman
Virtually none of the conclusions expressed here give me comfort.
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Hi Clandestino.
"There was drastic increase in drag and reduction in lift at extreme angle of attack. You may call it Mickey Mouse if it suits you but in every serious aerodynamic treatise it is called stall."
I said it did not resemble.a "normal Stall" (entry to). Of all possibilities relative to entry, 447 had a large ballistic component, she was losing (had lost) energy rapidly due to the trajectory, not due drag. This is where I was going when I posited she would have Stalled sooner, at higher speed, without the influence of the 'locked in UP'position THS. Without Full UP THS, if entering an aerodynamic STALL, the two expected cues to entry may have been experienced with enough crew recognition to provoke an actual STALL recovery from them. That is conjecture, but I think my argument is established as a possibility.
A ballistic STALL is gentle, almost graceful, and there is no "Drastic increase in drag", and no compelling urgency for the Nose to drop. Buffet is likewise attenuated, and as in this case, less likely to cause alarm, or alert. The AoA was extreme, and this causes the functional Cg to locate aft, further reducing the normal signals of STALL as well as make recovery more problematic. Think "Tail Slide", or "Hammerhead".
Just as there is no drastic increase in drag, there is likewise no dramatic loss of lift, the lift is almost gone. Again, there is a gentle transition to ballistic and g accelerated descent only.
I write this with great respect, you have added a great deal to the knowledge base, and I fear my emotions have at times affected my writing. Apologies if I have been rude.
I am interested in reading your opinion.
"There was drastic increase in drag and reduction in lift at extreme angle of attack. You may call it Mickey Mouse if it suits you but in every serious aerodynamic treatise it is called stall."
I said it did not resemble.a "normal Stall" (entry to). Of all possibilities relative to entry, 447 had a large ballistic component, she was losing (had lost) energy rapidly due to the trajectory, not due drag. This is where I was going when I posited she would have Stalled sooner, at higher speed, without the influence of the 'locked in UP'position THS. Without Full UP THS, if entering an aerodynamic STALL, the two expected cues to entry may have been experienced with enough crew recognition to provoke an actual STALL recovery from them. That is conjecture, but I think my argument is established as a possibility.
A ballistic STALL is gentle, almost graceful, and there is no "Drastic increase in drag", and no compelling urgency for the Nose to drop. Buffet is likewise attenuated, and as in this case, less likely to cause alarm, or alert. The AoA was extreme, and this causes the functional Cg to locate aft, further reducing the normal signals of STALL as well as make recovery more problematic. Think "Tail Slide", or "Hammerhead".
Just as there is no drastic increase in drag, there is likewise no dramatic loss of lift, the lift is almost gone. Again, there is a gentle transition to ballistic and g accelerated descent only.
I write this with great respect, you have added a great deal to the knowledge base, and I fear my emotions have at times affected my writing. Apologies if I have been rude.
I am interested in reading your opinion.
Last edited by Lyman; 29th Jul 2012 at 02:05.
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as they might still be subscribed to puerile notion of improving safety via legal punishment.
And for make this ( dispense justice fairly ) .. the judge (s) and lawyers need to have all evidences and expertise at hand
When judging a crime .. the judicial body will not examine some evidences and not some other .. this will be unfair ...
Idea is that investigators will duly report suspected criminal activities they come across and judges
And if the judge require the entire CVR for the need of justice .. he will ask for have it .. and his request can be positively answered ( Ref .. canadian court concerning AF A340 Toronto)
This does not mean that the entirety of the recording will make way to public
Last edited by jcjeant; 29th Jul 2012 at 05:37.
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Lyman
I really cannot agree with anything you have written here. Drag certainly increases dramatically when the wing stalls and the loss of energy came from an excess of drag over (thrust plus weight component along the flight path). For an explanation on the mechanics of wing stall on a modern airliner see Thread 5 #176 and 297 and Thread 6 #457. What evidence do you have to justify your claim that buffet is attenuated, when it is clear from the data published that there was a clear change in cockpit 'g' characteristics at the first stall and BEA stated in their final report that AI pilots had confirmed the (subjective) stall limit as severe buffet at 10 deg AoA? [I accept that on 447 it might have been masked by response to turbulence but that is not at all the same thing]. What on earth is 'functional Cg'? and how does AoA affect it?Are you postulating fuel slosh? and if you are would you like to put some numbers to it rather than vague speculations?
And wing stalling AoA is independent on whether the pitching moment necessary to get to that AoA is provided by THS, elevator or THS and elevator acting in concert. On AF447 BTW, once the aircraft had departed from initial trim the THS was giving a ND moment, offset by a lot of up elevator.
A ballistic STALL is gentle, almost graceful, and there is no "Drastic increase in drag", and no compelling urgency for the Nose to drop. Buffet is likewise attenuated, and as in this case, less likely to cause alarm, or alert. The AoA was extreme, and this causes the functional Cg to locate aft, further reducing the normal signals of STALL as well as make recovery more problematic.
And wing stalling AoA is independent on whether the pitching moment necessary to get to that AoA is provided by THS, elevator or THS and elevator acting in concert. On AF447 BTW, once the aircraft had departed from initial trim the THS was giving a ND moment, offset by a lot of up elevator.
Last edited by Owain Glyndwr; 29th Jul 2012 at 05:28.
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Originally Posted by Clandestino
If stick is pulled against the rear stop and nose is just bobbing around, you are out of control
This back and forth discussion on buffet is really irrelevant. The 'buffet' that is occupying so much etherspace here is the traditional 'buffet' we train for in classic stalls (at S&L stalling alphas) where the separated airflow from the wing 'plays' on a control surface such as the elevator or tailplane. Reference to mm's diagrams of the dynamics of an AoA of 40 degrees will show that in all probability the separated airflow missed the tail surfaces. Yes, it would sound and feel different. Those of us who have had the 'experience' of such will know that Lyman's quote "A ballistic STALL is gentle, almost graceful," is exactly correct and that is what 447 had. A totally different dynamic and one very few airline pilots will have experienced.
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Hi Clandestino,
How do your instructors insert a stall scenario without you realising?
I was referring to your general statement there are no surprises in sim. Well, my instructors have some latitude about failures they introduce during LOFT so it's not just about following the script for me.
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Originally Posted by BOAC
The 'buffet' that is occupying so much etherspace here is the traditional 'buffet' we train for in classic stalls (at S&L stalling alphas) where the separated airflow from the wing 'plays' on a control surface such as the elevator or tailplane.
An alternative view
The accident report and much of this debate has focused on UAS in that the crew failed to understand that situation.
However, I don’t recall the following alternative being considered.
The crew had not detected the UAS situation, but with ADC dropout/changeover the (unwarranted?) stall warning was taken as real. The PF commenced stall recovery, except erroneously applied power and pulled up with the intent of using the alpha protection – typical GPWS / windshear recovery – perhaps a stall recovery technique as perceived from training or other bias.
This assumes that the PF did not comprehend that the aircraft had reverted to Alt Law, even though it was alerted and called by the PNF. Thus there was no appreciation of the loss of stall protection and actuation of stall audio. Much of this behavior could be consistent with the aspects of surprise – confusion. This too could encourage the choice of an inappropriate manoeuvre, as could weak training, or biased understanding of the control system – sales talk / social chat pages.
It also questions if stall recovery in normal law was ever taught this way or discussion of ‘the aircraft won’t stall’ dominated the GPWS / windshear recovery training.
Subsequently in the event, when the aircraft stalled, the PF was further confused by the true stall warning; – according to him he had been flying the ‘correct’ maneuver.
Nose down stick stopped the warning, but nose up – the assumed correct recovery, gave a warning.
After the AoA cut out, the situation reversed. Moving the stick forward / lowering the nose, gave a stall warning (AoA reactivated), but nose up stopped it as the AoA cut out. This was the reverse of conventional logic, but supported the erroneous nose-up to recover course of action as being correct, as this stopped the stall warning. Hence there were many comments of confusion.
Thereafter we have history. This supposition identifies the difficulties of ensuring correct context in training, and correct recall in real situations – situation awareness. Also possible areas where the use of technology opens additional error paths – a choice of recovery techniques depending on the situation / control law; either a pull up in normal law using the control protections (GPWS / windshear recovery), or in alt law, when the aircraft might be stalled, requiring different and more circumspect action.
This is not to say that the technology is at fault, but more likely the human choice of how to use it (training / operations / regulators / manufacturers); and that this choice may increase mental workload in situations where quick clear thinking is more likely to be required.
However, I don’t recall the following alternative being considered.
The crew had not detected the UAS situation, but with ADC dropout/changeover the (unwarranted?) stall warning was taken as real. The PF commenced stall recovery, except erroneously applied power and pulled up with the intent of using the alpha protection – typical GPWS / windshear recovery – perhaps a stall recovery technique as perceived from training or other bias.
This assumes that the PF did not comprehend that the aircraft had reverted to Alt Law, even though it was alerted and called by the PNF. Thus there was no appreciation of the loss of stall protection and actuation of stall audio. Much of this behavior could be consistent with the aspects of surprise – confusion. This too could encourage the choice of an inappropriate manoeuvre, as could weak training, or biased understanding of the control system – sales talk / social chat pages.
It also questions if stall recovery in normal law was ever taught this way or discussion of ‘the aircraft won’t stall’ dominated the GPWS / windshear recovery training.
Subsequently in the event, when the aircraft stalled, the PF was further confused by the true stall warning; – according to him he had been flying the ‘correct’ maneuver.
Nose down stick stopped the warning, but nose up – the assumed correct recovery, gave a warning.
After the AoA cut out, the situation reversed. Moving the stick forward / lowering the nose, gave a stall warning (AoA reactivated), but nose up stopped it as the AoA cut out. This was the reverse of conventional logic, but supported the erroneous nose-up to recover course of action as being correct, as this stopped the stall warning. Hence there were many comments of confusion.
Thereafter we have history. This supposition identifies the difficulties of ensuring correct context in training, and correct recall in real situations – situation awareness. Also possible areas where the use of technology opens additional error paths – a choice of recovery techniques depending on the situation / control law; either a pull up in normal law using the control protections (GPWS / windshear recovery), or in alt law, when the aircraft might be stalled, requiring different and more circumspect action.
This is not to say that the technology is at fault, but more likely the human choice of how to use it (training / operations / regulators / manufacturers); and that this choice may increase mental workload in situations where quick clear thinking is more likely to be required.
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why would it not be?
Last edited by HazelNuts39; 29th Jul 2012 at 15:00.
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Originally Posted by HN39
IMHO it is highly probable that the buffet at AoA=6 degrees and M=0.6 is associated with locally supersonic flow.
Originally Posted by Lyman
This is where I was going when I posited she would have Stalled sooner, at higher speed, without the influence of the 'locked in UP'position THS.
Originally Posted by Lyman
A ballistic STALL is gentle, almost graceful,
Originally Posted by Lyman
The AoA was extreme, and this causes the functional Cg to locate aft,
Originally Posted by Lyman
further reducing the normal signals of STALL as well as make recovery more problematic. Think "Tail Slide", or "Hammerhead".
Quousque tandem abutere, Lyman, patientia nostra?
Originally Posted by jcjeant
The judicial court is not there for improve safety
Originally Posted by jcjeant
the judge (s) and lawyers need to have all evidences and expertise at hand
Originally Posted by BOAC
no - you are probably stalled. What if when they move the stick forwards and the nose goes down - were they still out of control?
Originally Posted by BOAC
"A ballistic STALL is gentle, almost graceful," is exactly correct
Originally Posted by BOAC
A totally different dynamic and one very few airline pilots will have experienced.
If you want to train it in aerobats, what's the use of practicing the maneuver that will be far more dangerous in far, far heavier and far less maneuverable aeroplane?
I have never practiced full stall recovery in my current type and don't ever intend to. There is no reasonable aviation authority anywhere in the world that will even attempt to make me do it.
Originally Posted by rudderrudderrat
How do your instructors insert a stall scenario without you realising?
Anyway, we are discussing AF447 here. That's where pilots were not startled by sudden unexpected stall warning but rather loss of reliable airspeed information made one of them pull until stalled and disregard the stall warning. Anyway, please find me an incident or accident where the first sign of trouble was stall warning (except 1011 at JFK where untimely warning was caused by faulty AoA probe).
Originally Posted by Safetypee
The crew had not detected the UAS situation, but with ADC dropout/changeover the (unwarranted?) stall warning was taken as real.
Originally Posted by Safetypee
biased understanding of the control system
Originally Posted by Safetypee
It also questions if stall recovery in normal law was ever taught this way
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BOAC,
The 'signature' of an oscillatory interaction between a shockwave and separated flow is different from what you describe as "the separated airflow from the wing 'plays' on a control surface such as the elevator or tailplane."
The 'signature' of an oscillatory interaction between a shockwave and separated flow is different from what you describe as "the separated airflow from the wing 'plays' on a control surface such as the elevator or tailplane."
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Well yes, having had many examples of both I quite agree. I'm afraid I'm still lost trying to see what the point you are trying to make is. I thought the on-going discussion was about the lack of 'traditional' buffet in the 'fully developed stall' in 447 at 40 degrees AoA? Why, then, are we considering 6 deg AoA at M0.6?