AF 447 Thread No. 8
Thanks OG
Thank you for your kind and detailed answer. I have nothing to add to the main part of your explanation, it is along my thinking.
Imho it is even more difficult, when we consider that the aircraft was not that stable at all. Well, it did not depart into some kind of spin, but looking at the traces we had rolling, banking and pitching movements of the aircraft, and those might have been present due to pilot action or despite pilot reaction on aircraft behaviour. Those aircraft movements and associated flight control deflections cause aditional drag and prolong any kind of recovery.
The assumption of instantaneous pitch down by 25° assumes, that enough authority is available even with thrust at TOGA, or when thrust would be in idle we would have to consider the later application of thrust, its effect on pitching moment and the spool up time, which again would influence the acceleration. We assume, a pilot in this situation can decrease the pitch in a most expedite way by 25° and maintain exactly -10° pitch over a time period of more then 30 seconds, while still stalled despite the fact, that his aircraft is in a degraded mode of operation (not to talk about the stress of the crew itself). Those 30 seconds with an unwinding altimeter would be like ages.
I buy that value, it is a fifty percent increase against the posted values in the graph. If we further consider, that the average descent rate at that time was around 15.000´/min (at 02:11:45 at 35372 feet, 22 seconds later at 02:12:07 at 29736 feet, and that those values where present without stuffing the nose down (which would increase initally the descentrate), we can assume an aditional altitude loss of at least 5.000 feet for time delays due to this unplanned stall situation any crew would be confronted with even after this discussion here.
In a practical sense we would end up somewhere between 20.000 and 10.000 feet when starting the recovery close to FL 350 and we might crash with the same procedure when stalling at FL 250.
My harsh assesment (no offence intended) would be, it might look good on a piece of paper in a warm office, but i doubt the practical use of it.
Reduce the AOA until stall warning stops, and the sooner it stops, the better it will be.
I´m not saying that those calculations are wrong in any way, but i dont think they will lead to a practical recovery technique.
That is, I think, the basic recovery mechanism, but in the early seconds the exact response depends on a changing balance between the various effects, and these in turn depend on the exact time history of applied pitch, so it is really quite difficult to answer your questions about the first twelve seconds.
The assumption of instantaneous pitch down by 25° assumes, that enough authority is available even with thrust at TOGA, or when thrust would be in idle we would have to consider the later application of thrust, its effect on pitching moment and the spool up time, which again would influence the acceleration. We assume, a pilot in this situation can decrease the pitch in a most expedite way by 25° and maintain exactly -10° pitch over a time period of more then 30 seconds, while still stalled despite the fact, that his aircraft is in a degraded mode of operation (not to talk about the stress of the crew itself). Those 30 seconds with an unwinding altimeter would be like ages.
I don't think PJ2 will be upset if I say that in my conversations with him he confirmed that on at least one occasion he executed a recovery from 30 deg AoA using 10 deg ND pitch - it took about 15000 ft.
In a practical sense we would end up somewhere between 20.000 and 10.000 feet when starting the recovery close to FL 350 and we might crash with the same procedure when stalling at FL 250.
My harsh assesment (no offence intended) would be, it might look good on a piece of paper in a warm office, but i doubt the practical use of it.
Reduce the AOA until stall warning stops, and the sooner it stops, the better it will be.
I´m not saying that those calculations are wrong in any way, but i dont think they will lead to a practical recovery technique.
Last edited by RetiredF4; 25th Apr 2012 at 18:50.
Stall recovery and AoA one mo' time
Glad to see we're back to recovery possibilities and maybe even probabilities.
Liked 'bird's and Retired's responses, a lot.
Unlike that little jet I flew long ago, the Airbus does not appear to have that "bucket" in the pitch moment characteristics. In other words, no "deep stall" and some semblance of pitch control by the humans besides those inputs otto is cranking in. Otherwise, why would the pilot even need to hold back stick? And it also appears that a few nose down( or even a few less nose up) inputs resulted in actual pitch changes, no?
The flaky AoA indications available and the system's disregard of AoA for a short time didn't help, but seems the speed indications came back fairly soon.
So I throw my hat in with 'bird and Retired and others postulating that a moderate nose down command and increase in thrust made recovery possible, and not requiring 20,000 friggin' feet. In other words, it was possible to fly out of the stall.
But ya gotta realize you are stalled! And seems some warnings were being blared on and off for the whole time. Apparently, the clue light never came on.
With the crappy AoA indications, all ya got is altitude and IAS/EAS/CAS ( pick one) to show you are making progress. No big deal, as once nose down 5 or even 10 degrees, the speed indications now available would show a slow but steady increase. And as O.G. points out, drag decreases immensely when lowering AoA from extreme values. I would imagine seeing a few knots increase every few seconds.
If I don't see some drastic changes in training and warnings to the crews about stalls and stall recoveries, I shall be greatly disappointed.
Liked 'bird's and Retired's responses, a lot.
Unlike that little jet I flew long ago, the Airbus does not appear to have that "bucket" in the pitch moment characteristics. In other words, no "deep stall" and some semblance of pitch control by the humans besides those inputs otto is cranking in. Otherwise, why would the pilot even need to hold back stick? And it also appears that a few nose down( or even a few less nose up) inputs resulted in actual pitch changes, no?
The flaky AoA indications available and the system's disregard of AoA for a short time didn't help, but seems the speed indications came back fairly soon.
So I throw my hat in with 'bird and Retired and others postulating that a moderate nose down command and increase in thrust made recovery possible, and not requiring 20,000 friggin' feet. In other words, it was possible to fly out of the stall.
But ya gotta realize you are stalled! And seems some warnings were being blared on and off for the whole time. Apparently, the clue light never came on.
With the crappy AoA indications, all ya got is altitude and IAS/EAS/CAS ( pick one) to show you are making progress. No big deal, as once nose down 5 or even 10 degrees, the speed indications now available would show a slow but steady increase. And as O.G. points out, drag decreases immensely when lowering AoA from extreme values. I would imagine seeing a few knots increase every few seconds.
If I don't see some drastic changes in training and warnings to the crews about stalls and stall recoveries, I shall be greatly disappointed.
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Originally Posted by OK465
Why doesn't Nzw go to 1 at zero FPA?
That was caused by an error in the mathematical model. Thanks for pointing out the error. The erroneous graphs have been replaced by corrected versions.
Last edited by HazelNuts39; 25th Apr 2012 at 21:04. Reason: Update
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Graphs
Would the performance graphs have looked different if they had been made following the suggestions in AB's" Safety First" -Page 10 issue Jan 2011 ?
These include :
"Autopilot and autothrottle...Off
Nose down pitch control...Apply until out of stall...
Nose down pitch trim...As needed ...( ...this will also address autopilot induced full back trim.)
Thrust.... As needed.....for engines installed below the wing applying maximum thrust can create a strong nose up pitching moment if the speed is low......
Speed Brake...Retract
Bank... Wings level Apply gentle action for recovery to avoid secondary stalls, then return to desired flight path."
The main differences appear to be Thrust and some contributors seem to think that 10 -15 degrees ND might be more appropriate or enough.
These include :
"Autopilot and autothrottle...Off
Nose down pitch control...Apply until out of stall...
Nose down pitch trim...As needed ...( ...this will also address autopilot induced full back trim.)
Thrust.... As needed.....for engines installed below the wing applying maximum thrust can create a strong nose up pitching moment if the speed is low......
Speed Brake...Retract
Bank... Wings level Apply gentle action for recovery to avoid secondary stalls, then return to desired flight path."
The main differences appear to be Thrust and some contributors seem to think that 10 -15 degrees ND might be more appropriate or enough.
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Lyman
Yes, you are missing something. I gave a description of stall on modern airliners is Post #294 of Thread 5.
Franzl
Yeah I agree the lateral behaviour complicates matters. A lot of that motion might be the natural response of the airframe when taken to those levels of AoA, not helped by the fact that the wing mounted roll controls would have been virtually ineffective and that the fin/rudder effectiveness was also compromised by their high effective sweep at high AoA. Not sure about drag, although there was a lot of scatter in the results which could have been disguised roll/sideslip effects, but also there might have been induced AoA effects.
Hey, I wasn’t assuming the aircraft could be pitched down instantaneously! That was a gross simplification to get the explanation across more easily. Neither would I assume that a pilot would in practice be able to maintain an exact nose down pitch. The sums, such as they were, were intended to give some idea of what MIGHT have been possible if mental blocks hadn’t got in the way not as actual recoveries.
The starting conditions included the rate of descent, so that bit shouldn’t apply. My typical calculation for recovery from FL350 took about 12000 ft, and I was fairly happy to say that looked reasonable against 15000 ft especially when one considers that the simulator modelling was probably even less representative than mine.
Let me put it clearly – my sums are intended to illustrate the sort of recovery that MIGHT have been possible. I am only too aware of their shortcomings. But even so I think they are a good indication that, as Gums says, the aircraft could have been flown out of it – if only!
Well I leave that to others more skilled than I in practical piloting.
Reduce the AOA until stall warning stops, and the sooner it stops, the better it will be.
No natural tendency to lower its nose in Stall? Are you sure? I thought that was one of the cues for a Stall suss. Is there something I am missing re: CG?
Franzl
Imho it is even more difficult, when we consider that the aircraft was not that stable at all. Well, it did not depart into some kind of spin, but looking at the traces we had rolling, banking and pitching movements of the aircraft, and those might have been present due to pilot action or despite pilot reaction on aircraft behaviour. Those aircraft movements and associated flight control deflections cause aditional drag and prolong any kind of recovery.
The assumption of instantaneous pitch down by 25° assumes, that enough authority is available even with thrust at TOGA, or when thrust would be in idle we would have to consider the later application of thrust, its effect on pitching moment and the spool up time, which again would influence the acceleration. We assume, a pilot in this situation can decrease the pitch in a most expedite way by 25° and maintain exactly -10° pitch over a time period of more then 30 seconds, while still stalled despite the fact, that his aircraft is in a degraded mode of operation (not to talk about the stress of the crew itself). Those 30 seconds with an unwinding altimeter would be like ages.
I buy that value, it is a fifty percent increase against the posted values in the graph. If we further consider, that the average descent rate at that time was around 15.000´/min (at 02:11:45 at 35372 feet, 22 seconds later at 02:12:07 at 29736 feet, and that those values where present without stuffing the nose down (which would increase initally the descentrate), we can assume an aditional altitude loss of at least 5.000 feet for time delays due to this unplanned stall situation any crew would be confronted with even after this discussion here.
The starting conditions included the rate of descent, so that bit shouldn’t apply. My typical calculation for recovery from FL350 took about 12000 ft, and I was fairly happy to say that looked reasonable against 15000 ft especially when one considers that the simulator modelling was probably even less representative than mine.
Let me put it clearly – my sums are intended to illustrate the sort of recovery that MIGHT have been possible. I am only too aware of their shortcomings. But even so I think they are a good indication that, as Gums says, the aircraft could have been flown out of it – if only!
My harsh assesment (no offence intended) would be, it might look good on a piece of paper in a warm office, but i doubt the practical use of it.
Well I leave that to others more skilled than I in practical piloting.
Reduce the AOA until stall warning stops, and the sooner it stops, the better it will be.
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If the A330-200 is balanced similarly to the A320, the nose will pitch down upon stall as long as the CoG is not set too far aft (it was well within the limit as I recall). In the A320 sim I had to work quite hard on the sidestick to keep the nose at 15 degrees up both on approach to and during the stall.
Lyman, if they were trying to avoid stalling, they were going about it in a very unusual manner - in fact they were doing precisely the opposite of what they should have been doing. Coupled with the "crazy speed" remarks, I think the PF, at least, was fighting a non-existent overspeed.
Lyman, if they were trying to avoid stalling, they were going about it in a very unusual manner - in fact they were doing precisely the opposite of what they should have been doing. Coupled with the "crazy speed" remarks, I think the PF, at least, was fighting a non-existent overspeed.
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"Well I leave that to others more skilled than I in practical piloting.
Reduce the AOA until stall warning stops, and the sooner it stops, the better it will be."
They decided to hold the side stick full back for some reason and continued to do so with impact with the Atlantic Ocean. Several minutes was not enough time for them to figure it out. Too bad the passengers didn't understand who would be commanding their aircraft that day. How can you justify that lack of skill?
Reduce the AOA until stall warning stops, and the sooner it stops, the better it will be."
They decided to hold the side stick full back for some reason and continued to do so with impact with the Atlantic Ocean. Several minutes was not enough time for them to figure it out. Too bad the passengers didn't understand who would be commanding their aircraft that day. How can you justify that lack of skill?
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Dozy sayeth:
Well, whyinheck would they be similar? Two entirely different airframes, aren't they?
If the A330-200 is balanced similarly to the A320, the nose will pitch down upon stall as long as the CoG is not set too far aft...
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I'd have tested in an A330 sim, but there wasn't one available.
Also worth bearing in mind that according to the DFDR traces, the nose did come down below the horizon several times during the stall, even with the THS at 13 degrees nose up. None of the nose-down inputs were enough or held long enough to have commanded the pitch-down achieved, so I think it's reasonable to assume that the A330 is fairly benign in terms of stall characteristics.
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Dozy. Yes, she wanted to fly, and without lift and tail to keep her flying, she will fall, nose first, of course. Agreed. So it becomes ever more important to suss the "place" of the crew. HF.
The starting conditions included the rate of descent, so that bit shouldn’t apply. My typical calculation for recovery from FL350 took about 12000 ft, and I was fairly happy to say that looked reasonable against 15000 ft especially when one considers that the simulator modelling was probably even less representative than mine.
That is certainly an intriguing statement.
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Well, the sim I was in certainly got the gist of it, even if the numbers might not have been that exact. Specifically the loss of effective aileron control once established in the stall, necessitating use of rudder (albeit *very* gingerly) to level the wings. We know that the crew didn't try using rudder until very late in the sequence, and that some very aggressive aileron roll inputs were made, which might have mad a bad situation worse.
We all know that when that far outside of the flight envelope, the data is based on extrapolation from the numbers gleaned in flight testing rather than real numbers - but that doesn't mean the sim cannot be a useful learning tool.
I don't doubt that the PF and the rest of the crew were doing everything they could think of to rescue the situation - the question is why did their training not encompass the *correct* things to do?
We all know that when that far outside of the flight envelope, the data is based on extrapolation from the numbers gleaned in flight testing rather than real numbers - but that doesn't mean the sim cannot be a useful learning tool.
I don't doubt that the PF and the rest of the crew were doing everything they could think of to rescue the situation - the question is why did their training not encompass the *correct* things to do?
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Dozy.
Their training no doubt did include recovery from STALL, if not the 330, other airworthy examples that would translate to 330. The training that lacked was high altitude manual handling, and a complete understanding of the UAS. The rough handling can be laid at the PF, but the lack of a proper syllabus to include a fully understood UAS was not given, if even available. I think with gentle handling the rest may not have happened. There is a very suspicious lack of training re: STALL recognition, but as said, it shouldn't have STALLED.
No?
Their training no doubt did include recovery from STALL, if not the 330, other airworthy examples that would translate to 330. The training that lacked was high altitude manual handling, and a complete understanding of the UAS. The rough handling can be laid at the PF, but the lack of a proper syllabus to include a fully understood UAS was not given, if even available. I think with gentle handling the rest may not have happened. There is a very suspicious lack of training re: STALL recognition, but as said, it shouldn't have STALLED.
No?
Originally Posted by HazelNuts39
Clandestino,
For distribution of liquid water and ice particles in convective clouds, read IR#3 page 50.
For distribution of liquid water and ice particles in convective clouds, read IR#3 page 50.
So let's take this line of discussion a bit forward; page 50 of interim 3 deals with general distribution of water and ice particles in convective cloud, as introduction to principles of operation of Wx radar.
Interestingly, BEA findings on the conditions that were most likely encountered by AF447 crew is also on page 50 but of interim 2.
Originally Posted by BEA
The crews reported not observing any significant radar echoes on the
chosen flight path(8) but to have identified active zones nearby or lower,
which is also noted in a study by Météo France on these events undertaken
at the request of the BEA;
(8)Some crews had deviated from the planned flight path for meteorological reasons before the events occurred.
chosen flight path(8) but to have identified active zones nearby or lower,
which is also noted in a study by Météo France on these events undertaken
at the request of the BEA;
(8)Some crews had deviated from the planned flight path for meteorological reasons before the events occurred.
Originally Posted by DozyWannabe
I don't doubt that the PF and the rest of the crew were doing everything they could think of to rescue the situation - the question is why did their training not encompass the *correct* things to do?
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I don't think it is being (and I don't think you do either). The BEA's output thus far seems to be much more nuanced than that. Combine that with the sheer amount of time spent on this (by which I mean if it was considered a simple case of pilot error, the final report would have followed hot on the heels of interim #3), along with the collaboration between Airbus and Boeing regarding UAS and stall procedures - and I think we're looking at a landmark report here, once it finally arrives.
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Dozy
There is a big difference between an uncontrollable nose down pitch when the aircraft stalls in the classic manner and the need to hold back stick in ever increasing amounts as AoA is increased.
The former is a sort of instability the latter a natural characteristic of a stable airplane. The A330 and A320 are alike in this respect and if you go back to that pseudo-pitching moment curve I posted many moons ago (and which mm43 referred to more recently) you will find a continuous relationship between elevator (sidestick) position and AoA.
I had to work quite hard on the sidestick to keep the nose at 15 degrees up both on approach to and during the stall.
The former is a sort of instability the latter a natural characteristic of a stable airplane. The A330 and A320 are alike in this respect and if you go back to that pseudo-pitching moment curve I posted many moons ago (and which mm43 referred to more recently) you will find a continuous relationship between elevator (sidestick) position and AoA.
Last edited by Owain Glyndwr; 26th Apr 2012 at 06:55. Reason: spelling
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bubbers44
I'm not trying to - as I said I leave that to others who know more about it. Doesn't stop me having an opinion though!
How can you justify that lack of skill?
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OK465
Not meant to imply anything more than that the simulator aerodynamic model would have been validated up to the stall but not beyond and that (for us) the simulator modelling beyond that is unknown so we cannot assess how realistic the response might be.
In that respect, and in that respect only, my simplified model might be equally representative to the simulator in that there was at least an attempt to use realistic post stall aerodynamics.
That is certainly an intriguing statement. 
In that respect, and in that respect only, my simplified model might be equally representative to the simulator in that there was at least an attempt to use realistic post stall aerodynamics.
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If he was fighting an overspeed, why would he select TOGA?
Coupled with the "crazy speed" remarks
Aircraft operating in an environment has three dimensions
Vertical speed ?
Horizontal speed ?
Lateral speed ?
The combination of the three ?
I've said in other posts
The extracts of the BEA CVR show a dialogue crazy .. or as coming from people who are not in a same place
"You are going up
I'm going up?
I then descends"
And this continues throughout the recording
So when we study the CVR .. it does not really help understand what has happened ... instead it gets complicated