AF 447 Thread No. 6
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If anyone is wondering (like me) to what extent AF447 might have been different if THS had not autotrimmed beyond stall warning, look up
Owain Glyndwr's post #450, from which the following is quoted:
Owain Glyndwr's post #450, from which the following is quoted:
The nose was being held up by the application of elevator.
Of course, the THS setting made the elevator’s job easier, and if the THS had been (sensibly in my view) restricted to 3 deg the eventual AOA would have been lower, How much lower you can get from the first chart – with 3 deg THS and 30 deg elevator you could expect to arrive at 35 deg AOA – big deal! – you are still well stalled and although the descent would have been shallower the end would have been the same unless he had recognised early on that he was in a stall.
Of course, the THS setting made the elevator’s job easier, and if the THS had been (sensibly in my view) restricted to 3 deg the eventual AOA would have been lower, How much lower you can get from the first chart – with 3 deg THS and 30 deg elevator you could expect to arrive at 35 deg AOA – big deal! – you are still well stalled and although the descent would have been shallower the end would have been the same unless he had recognised early on that he was in a stall.
DW
Dozy,
there is no situation in cruise, where autotrim is improving a situation in ALT2 like that encountered by AF 447. If you can think of one, let me know. As we know, autotrim is inhibited in ALt1 at V-prot anyway and in direct law as well.
Then let´s look at it from the other way around.
How difficult would it be to expand the present feature from ALT1 to situations in ALT2 maybe with different and independent values? Is it rocket science?
Concerning your graceful degradation explain this degradation with autotrim of the THS:
In Normal LAW autotrim (a rally nice feature)
In ALT1 Law autotrim prohibit at VC-prot (looks sound to protect from entering unknown territory)
In ALT2 Law autotrim (that is your part to explain)
In Direct LAW autotrim off (looks sound to protect from entering unknown territory)
I would name that one non linear degradation (far off from gracefull).
Concerning your naming manual trim again, please do not push aside the inputs made to that issue from Clandestino. http://www.pprune.org/6770409-post394.html
Quote:
.
That should straighten up the manual trim option once and for all. It´s even worse, because the functioning autotrim in ALT 2 prevents manual trim in its original sense of implementation.
There might be pilots insane enough to pull on the yoke or sidestick in conventional and FBW aircraft until the aircraft stalls, but no one would trim while pulling.
To understand that above statement let me explain normal trim behaviour. With the intention to climb the pilot uses the yoke to change the pitch, once that change is reached he uses the trim to get rid of the pressure on the yoke. The trim comes into play when the change is achieved and not in the timeframe, where the change takes place.
In case of AF447 without autotrim the pilot would never ever have tried to achieve the desired flight path change with manual trim, because that is not the way to do it.
there is no situation in cruise, where autotrim is improving a situation in ALT2 like that encountered by AF 447. If you can think of one, let me know. As we know, autotrim is inhibited in ALt1 at V-prot anyway and in direct law as well.
Then let´s look at it from the other way around.
How difficult would it be to expand the present feature from ALT1 to situations in ALT2 maybe with different and independent values? Is it rocket science?
Concerning your graceful degradation explain this degradation with autotrim of the THS:
In Normal LAW autotrim (a rally nice feature)
In ALT1 Law autotrim prohibit at VC-prot (looks sound to protect from entering unknown territory)
In ALT2 Law autotrim (that is your part to explain)
In Direct LAW autotrim off (looks sound to protect from entering unknown territory)
I would name that one non linear degradation (far off from gracefull).
Concerning your naming manual trim again, please do not push aside the inputs made to that issue from Clandestino. http://www.pprune.org/6770409-post394.html
Quote:
Originally Posted by RetiredF4
Manual THS trim (nowhere mentioned in the books except in direct law, and never trained)
Clandestino:
Rest of youth post is spot-on, I just have to comment on this. It is not trained because it doesn't work. You can forcibly move the wheel to position of your choice but the FBW will return it to the position it deems to be necessary once you loose your grip and all the while will try to combat the trim with elevator to satisfy G demand.
There's no use and no need for manual trim while auto-trim is working.
Manual THS trim (nowhere mentioned in the books except in direct law, and never trained)
Clandestino:
Rest of youth post is spot-on, I just have to comment on this. It is not trained because it doesn't work. You can forcibly move the wheel to position of your choice but the FBW will return it to the position it deems to be necessary once you loose your grip and all the while will try to combat the trim with elevator to satisfy G demand.
There's no use and no need for manual trim while auto-trim is working.
That should straighten up the manual trim option once and for all. It´s even worse, because the functioning autotrim in ALT 2 prevents manual trim in its original sense of implementation.
There might be pilots insane enough to pull on the yoke or sidestick in conventional and FBW aircraft until the aircraft stalls, but no one would trim while pulling.
To understand that above statement let me explain normal trim behaviour. With the intention to climb the pilot uses the yoke to change the pitch, once that change is reached he uses the trim to get rid of the pressure on the yoke. The trim comes into play when the change is achieved and not in the timeframe, where the change takes place.
In case of AF447 without autotrim the pilot would never ever have tried to achieve the desired flight path change with manual trim, because that is not the way to do it.
Last edited by RetiredF4; 31st Oct 2011 at 22:31.
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Personal insults
Mr. Wannabe said,
I'm already familiar with it, thanks for the advice anyway. I left your period where you put it, out of courtesy.
Assuming facts not in evidence, sir. I never said that I did. In fact, my cranium is so large I've been confined to the barn for years.
Look up the concept of "graceful degradation".
With a head that big, I'm surprised you fit through an average-sized door.
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It is not ALT2 in itself that causes the loss of low speed stability and the uninhibited travel of the THS. It is only the loss of 2 or more ADRs that causes this specific condition. It is possible to be in ALT2 with a THS that behaves as in ALT1.
To say that no pilot would trim nose-up while pulling is a bit presumptious i think. I do not find it inconceivable at all that the PF would have trimmed nose-up, perhaps even to the same extent the autotrim did, if he had the means to do so. He was after all back to mechanical stop on the stick for a full 30 seconds.
Not much a what he did was the way to do it, but he did it nonetheless.
To say that no pilot would trim nose-up while pulling is a bit presumptious i think. I do not find it inconceivable at all that the PF would have trimmed nose-up, perhaps even to the same extent the autotrim did, if he had the means to do so. He was after all back to mechanical stop on the stick for a full 30 seconds.
Not much a what he did was the way to do it, but he did it nonetheless.
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Franzl,
The FCU has no concept of "cruise", as far as I am aware. It is a real-time processing system that does the job it was designed to do very well, but it is intentionally quite a simple beast in terms of design (because the simpler a system is, the less things there are to go wrong).
You have to look at this from a systems perspective to understand. Autotrim as a system is never "inhibited" in any law other than Direct and Manual Trim Only - it is the *protections* that prohibit the aircraft from leaving the flight envelope by preventing any commands - either manual or automatic - from doing so, and if necessary providing corrective commands to keep the aircraft within the flight envelope. The protections are a completely discrete subsystem that is loosely-coupled to the others that make up the FCU system.
Again, that is not correct if you look at the architecture as a whole. I'll repeat for clarity - Autotrim as a system is not "prohibited", nor "turned off" in any other mode or Law than Direct or Manual Trim mode. If the protections are active, then the autotrim commands will be treated as any other command that takes the aircraft out of the flight envelope and corrected accordingly. Think of it as two separate processes running alongside each other rather than as an integrated whole.
Put even more simply, imagine two people on either side of a wall that has a two-handled saw poking through it. The person on one side (let's call him Otto Trim) is told to push the saw forward and the person on the other side (who is physically stronger and called Pete Tection) is told to not let the saw through past, say, two-thirds of it's length. Pete will always stop the saw at the limit and will try to return it to the prescribed position if it goes past, but he is not explicitly aware that Otto's on the other side trying to push it because the wall is in the way, and as such does not interfere or communicate with Otto directly - all Pete knows is that he mustn't let it through past a certain point.
What do you mean by "original sense of implementation"? Using manual trim to set the THS to a certain degree of pitch and letting go will cause the autotrim to try to hold that pitch, unless a demand is then made on the sidestick for which the autotrim will try to compensate. It doesn't "remember" what it was doing X number of seconds or minutes ago, it simply tries to hold the trim set by the autoflight or pilot commands.
In any case, using manual trim and then holding on to the wheel will prevent the autotrim from re-engaging.
"No pilot would ever..." is an impossible statement to prove.
I know you're not intending to patronise me, but I am fully aware of how trim works in the conventional sense - I even did it once or twice in the Chippy. Here there is no tactile feedback, so "trimming to the pressure" is impossible, and performing the same thing visually using the ADI as reference would be physically exhausting on a day-in, day-out basis. This was part of the reason autotrim was developed because the flight control design was a completely new paradigm.
The only way you could possibly know that is with a Ouija board. The last time he trimmed manually would have either been during type conversion training, recurrent training or even back when he was flying trainers - because the Airbus FBW flight control paradigm does not require it except in case of major failure.
If all goes to plan I'm going to be doing some exciting research this weekend and I'll be able to argue from a much surer footing. If it turns out I've been wrong about anything you guys will be the first to know.
@Organfreak - Those were not intended to be personal insults, but I must confess I was flabberghasted with the throwaway manner in which you described the Airbus system design and those who developed it. I emphatically request you find out who Gordon Corps was, what he accomplished and how he died - and if you have the time, have a browse through the Flight International archives relating to A320 development (in which he figures very prominently) before you put your foot in it again.
If you can think of one, let me know. As we know, autotrim is inhibited in ALt1 at V-prot anyway and in direct law as well.
Concerning your graceful degradation explain this degradation with autotrim of the THS:
In Normal LAW autotrim (a rally nice feature)
In ALT1 Law autotrim prohibit at VC-prot (looks sound to protect from entering unknown territory)
In ALT2 Law autotrim (that is your part to explain)
In Direct LAW autotrim off (looks sound to protect from entering unknown territory)
In Normal LAW autotrim (a rally nice feature)
In ALT1 Law autotrim prohibit at VC-prot (looks sound to protect from entering unknown territory)
In ALT2 Law autotrim (that is your part to explain)
In Direct LAW autotrim off (looks sound to protect from entering unknown territory)
Put even more simply, imagine two people on either side of a wall that has a two-handled saw poking through it. The person on one side (let's call him Otto Trim) is told to push the saw forward and the person on the other side (who is physically stronger and called Pete Tection) is told to not let the saw through past, say, two-thirds of it's length. Pete will always stop the saw at the limit and will try to return it to the prescribed position if it goes past, but he is not explicitly aware that Otto's on the other side trying to push it because the wall is in the way, and as such does not interfere or communicate with Otto directly - all Pete knows is that he mustn't let it through past a certain point.
That should straighten up the manual trim option once and for all. It´s even worse, because the functioning autotrim in ALT 2 prevents manual trim in its original sense of implementation.
In any case, using manual trim and then holding on to the wheel will prevent the autotrim from re-engaging.
There might be pilots insane enough to pull on the yoke or sidestick in conventional and FBW aircraft until the aircraft stalls, but no one would trim while pulling.
To understand that above statement let me explain normal trim behaviour. With the intention to climb the pilot uses the yoke to change the pitch, once that change is reached he uses the trim to get rid of the pressure on the yoke. The trim comes into play when the change is achieved and not in the timeframe, where the change takes place.
In case of AF447 without autotrim the pilot would never ever have tried to achieve the desired flight path change with manual trim, because that is not the way to do it.
If all goes to plan I'm going to be doing some exciting research this weekend and I'll be able to argue from a much surer footing. If it turns out I've been wrong about anything you guys will be the first to know.
@Organfreak - Those were not intended to be personal insults, but I must confess I was flabberghasted with the throwaway manner in which you described the Airbus system design and those who developed it. I emphatically request you find out who Gordon Corps was, what he accomplished and how he died - and if you have the time, have a browse through the Flight International archives relating to A320 development (in which he figures very prominently) before you put your foot in it again.
Last edited by DozyWannabe; 1st Nov 2011 at 01:53.
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takata re: SPIKES.
The Airbus has this elegant escape from CFIT? NON?
Max power, roll full, and pull back max.
A max effort, 'at the limits' safety manuever. During which the a/c nibbles at Stall? and wing drop? No sweat, the Bus knows SPIKES.
The Pilot doesn't. As above, for Alternate Law, the STALL WARNING needs some looking into.
The Airbus has this elegant escape from CFIT? NON?
Max power, roll full, and pull back max.
A max effort, 'at the limits' safety manuever. During which the a/c nibbles at Stall? and wing drop? No sweat, the Bus knows SPIKES.
The Pilot doesn't. As above, for Alternate Law, the STALL WARNING needs some looking into.
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Hamburt Spinkleman. Howdy. Isn't STALL WARN inhibited in Protection?
G Prot? Vc Prot? Load Factor Prot? The pilots did not hear the STALL WARN at the top of climb, Right? It shows in the trace, but where is the SV Cricket inhibited? On which side of the FDR? Is it silenced at the panel?
Thanks, hope you can help.
G Prot? Vc Prot? Load Factor Prot? The pilots did not hear the STALL WARN at the top of climb, Right? It shows in the trace, but where is the SV Cricket inhibited? On which side of the FDR? Is it silenced at the panel?
Thanks, hope you can help.
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The Stall Warning and "cricket" annunciation is on the d*mn CVR - if they were picked up on the CAM or the hot mikes, it was audible in the flight deck. Must try harder.
Radio silence resumed.
Radio silence resumed.
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They clearly did not hear the WARN, and I do believe that the WARN is inhibited in prot, but you would know that?
Did you hear it?
You have been given one of three things, the 'annunciations'.
You are entirely willing to accept two absurdities to believe the one.
1. They did not hear it.
2. They heard it, but ignored it, without comment.
This is acceptable to you, because you are wanting to stop at what makes your position correct.
You have no desire to hear or see further, your mind is made.
There is one mind that will foreclose all doubt, the one that will be correct at all costs, even prior to investigation.
Did you hear it?
You have been given one of three things, the 'annunciations'.
You are entirely willing to accept two absurdities to believe the one.
1. They did not hear it.
2. They heard it, but ignored it, without comment.
This is acceptable to you, because you are wanting to stop at what makes your position correct.
You have no desire to hear or see further, your mind is made.
There is one mind that will foreclose all doubt, the one that will be correct at all costs, even prior to investigation.
Originally Posted by Dozy
Here there is no tactile feedback, so "trimming to the pressure" is impossible, and performing the same thing visually using the ADI as reference would be physically exhausting on a day-in, day-out basis. This was part of the reason autotrim was developed because the flight control design was a completely new paradigm.
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Au contraire, sir - I'd *love* to know why they didn't hear it - and if it didn't sound then I'd be the first to say that would be a major problem. But unless you're accusing the BEA of falsifying evidence, then the presence of the Stall Warning alarm on the CVR is a documented fact, which closes that line of enquiry and this conversation.
@Capn Bloggs - As with any work, on the line I'm sure you'll encounter super-competent pilots, pilots who shouldn't be allowed in a flight deck and pilots of every level inbetween, with most hovering around an average competency level (which in most cases requires more general competence than a lot of jobs). However, you'd think that "No pilot would...":
and yet pilots have done all of those things, and some pilots have repeated the same mistakes made by their predecessors. This is not to say I think pilots are incompetent, far from it - because of the staggering number of flights that get to their destinations safely every day - but "No pilot would..." turns out to be a demonstrably false assertion. "No pilot *should*..." on the other hand, and you won't hear me arguing.
To go back to your question, the change in paradigm was based on a desire to start from a "clean sheet" when it comes to flight deck ergonomics based on the technological leaps made during the Space Age, not because of any desire to impugn pilots as a whole.
@Capn Bloggs - As with any work, on the line I'm sure you'll encounter super-competent pilots, pilots who shouldn't be allowed in a flight deck and pilots of every level inbetween, with most hovering around an average competency level (which in most cases requires more general competence than a lot of jobs). However, you'd think that "No pilot would...":
- Take off without permission
- Retract LE devices below a safe speed
- Fail to deploy high lift devices at all prior to take-off
- Fail to turn on engine anti-ice when taking off into a blizzard
- Shut down a healthy engine and leave the damaged one running
and yet pilots have done all of those things, and some pilots have repeated the same mistakes made by their predecessors. This is not to say I think pilots are incompetent, far from it - because of the staggering number of flights that get to their destinations safely every day - but "No pilot would..." turns out to be a demonstrably false assertion. "No pilot *should*..." on the other hand, and you won't hear me arguing.
To go back to your question, the change in paradigm was based on a desire to start from a "clean sheet" when it comes to flight deck ergonomics based on the technological leaps made during the Space Age, not because of any desire to impugn pilots as a whole.
Last edited by DozyWannabe; 1st Nov 2011 at 01:44.
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For pitys sake.
If a pilot is holding the yoke full aft, that tells a story.
If a pilot is holding his wrist half-cocked back ,in a pocket in the corner of the cockpit, at night. that's another story.
You can yarn it however you like , but that's how it is.
If a pilot is holding the yoke full aft, that tells a story.
If a pilot is holding his wrist half-cocked back ,in a pocket in the corner of the cockpit, at night. that's another story.
You can yarn it however you like , but that's how it is.
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@BarbiesBoyfriend
The ending of the story (aircraft pitches up to an attitude that has no business being achieved in cruise) is the same in both cases however. The proper response to the story ("That's not right - are you really doing that? I have control.") is the same.
The ending of the story (aircraft pitches up to an attitude that has no business being achieved in cruise) is the same in both cases however. The proper response to the story ("That's not right - are you really doing that? I have control.") is the same.
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Originally Posted by Dozy
"That's not right - are you really doing that? I have control."
Also, pilots do silly stuff, let them do those by themselves, automation is here to help not to put you deeper in the mud.
Let him trim by hand if that's really what he wants.
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Think about it logically - the difference between looking over at the yoke to confirm what you're seeing on the ADI or out the window (unless you're watching your colleague's inputs like a hawk, which I suspect isn't the case given the average PNF workload) and asking them directly is what - a second, maybe two?
Also, pilots do silly stuff, let them do those by themselves, automation is here to help not to put you deeper in the mud.
As part of the research I was talking about, it is possible that the A320's equivalent of Alt 2 (Alternate with no speed stability) may function differently when it comes to trim, I'll keep you updated.
Let him trim by hand if that's really what he wants.
Because someone above either of our paygrades on both the pilot and engineering side decided that the benefits outweighed the drawbacks.
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Those who think yokes should be the cure-all for what the other guy is doing should look at this accident originally posted by Netstruggler in the current Rumors & News AF447 thread.
http://libraryonline.erau.edu/online...s/AAR97-05.pdf
An interesting mix of Perpignan and AF447 on a DC-8 airframe. No loss of airspeed, but a stall warning failure combined with a PF who didn't let the nose down promptly at the stall and two staff pilots + a FE on a Post Maintenance Check Flight.
The guy in charge (PNF) didn't apparently realize that they were still stalled and allowed the PF to continue to hold the Yoke too far back to recover.
When the wings started rocking-it was like they had both forgotten all they should know.
Oh yes, PF had trimmed too far nose up. Do you see a possible pattern?
http://libraryonline.erau.edu/online...s/AAR97-05.pdf
An interesting mix of Perpignan and AF447 on a DC-8 airframe. No loss of airspeed, but a stall warning failure combined with a PF who didn't let the nose down promptly at the stall and two staff pilots + a FE on a Post Maintenance Check Flight.
The guy in charge (PNF) didn't apparently realize that they were still stalled and allowed the PF to continue to hold the Yoke too far back to recover.
When the wings started rocking-it was like they had both forgotten all they should know.
Oh yes, PF had trimmed too far nose up. Do you see a possible pattern?
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Originally Posted by Machinbird
Oh yes, PF had trimmed too far nose up. Do you see a possible pattern?
Some of the conclusions sound quite familiar:
The pilot flying applied inappropriate control column back
pressure during the stall recovery attempt in an inadequate
performance of the stall recovery procedure established in ABX’s
operations manual.
pressure during the stall recovery attempt in an inadequate
performance of the stall recovery procedure established in ABX’s
operations manual.
Although the pilot flying trimmed the airplane below the
recommended minimum trim speed for the clean stall, this action
did not contribute to the accident.
recommended minimum trim speed for the clean stall, this action
did not contribute to the accident.
The pilot not flying, as the pilot-in-command, failed to recognize,
address and correct the pilot flying’s inappropriate control inputs.
address and correct the pilot flying’s inappropriate control inputs.
The inoperative stall warning system failed to reinforce to the
flightcrew the indications that the airplane was in a full stall during
the recovery attempt
flightcrew the indications that the airplane was in a full stall during
the recovery attempt
This accident might have been prevented if the flightcrew had been
provided a clear, direct indication of the airplane’s angle of attack.
provided a clear, direct indication of the airplane’s angle of attack.
Refocus?
There seems to be a tendency to let the mass of opinion become fact...
- Autotrim did not stall the airplane, the PF did that quite successfully and then held the SS NU for a good long time, resulting in the NU trim eventually. The stall would have occurred with or without autotrim. My opinion is this is a distraction and something for the anti-Airbus brigade to fixate on. That the PNF did not notice the eventual trim demand seems to be a topic that has received scant attention - I believe those trim wheels would have been rotating for a good while. But no comment???
- The stall warning system worked and sounded at one point for, what was it, 53-54 seconds continuously, with no comment from PF or PNF? Eventually the damn thing gave up since the airspeed dropped below the 60kt cutoff, but come on!!!... From then on the vertical speed and pitch attitude should have told ANYONE with half an understanding of the basic laws of aerodynamics that the airplane was no longer flying in the true sense and was stalled.
- I am also surprised that the PNF never seemed to really comment on the initial zoom-climb? Why not? Nothing like "Hey, we're at FL380 what are you doing?"
There seems to a lot that the PNF didn't do? Question the climb, question the stall warning, the pitch/VS combination. Unfortunately, he seems to have been somewhat fixated on the necessity to call the Captain back to the cockpit, just at the time when his full attention should have been on what the aircraft was doing.
- Autotrim did not stall the airplane, the PF did that quite successfully and then held the SS NU for a good long time, resulting in the NU trim eventually. The stall would have occurred with or without autotrim. My opinion is this is a distraction and something for the anti-Airbus brigade to fixate on. That the PNF did not notice the eventual trim demand seems to be a topic that has received scant attention - I believe those trim wheels would have been rotating for a good while. But no comment???
- The stall warning system worked and sounded at one point for, what was it, 53-54 seconds continuously, with no comment from PF or PNF? Eventually the damn thing gave up since the airspeed dropped below the 60kt cutoff, but come on!!!... From then on the vertical speed and pitch attitude should have told ANYONE with half an understanding of the basic laws of aerodynamics that the airplane was no longer flying in the true sense and was stalled.
- I am also surprised that the PNF never seemed to really comment on the initial zoom-climb? Why not? Nothing like "Hey, we're at FL380 what are you doing?"
There seems to a lot that the PNF didn't do? Question the climb, question the stall warning, the pitch/VS combination. Unfortunately, he seems to have been somewhat fixated on the necessity to call the Captain back to the cockpit, just at the time when his full attention should have been on what the aircraft was doing.
Last edited by GarageYears; 1st Nov 2011 at 13:27. Reason: Betterer English!
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Machinbird Zorin_75
It is a fascinating report netstruggler gave us the opportunity to read.
It is a reminder that stalling an airliner, intentionally or not, is a very serious matter.
You are correct, it cannot be the miraculous solution.
But it is one of the great piece of equipment that a multicrew has in its toolbox.
It is free non verbal communication between all in the flight deck.
The yokes have the merit to make that information available.
The sidesticks have the default to supress it.
In my book, an aft control column, is the best shot to wake me up.
It is a fascinating report netstruggler gave us the opportunity to read.
It is a reminder that stalling an airliner, intentionally or not, is a very serious matter.
Originally Posted by Machinbird
Those who think yokes should be the cure-all for what the other guy is doing ...
But it is one of the great piece of equipment that a multicrew has in its toolbox.
It is free non verbal communication between all in the flight deck.
The yokes have the merit to make that information available.
The sidesticks have the default to supress it.
Originally Posted by Page 35
During the attempted stall recovery, there were several indications of the PF’s excessive aft control column inputs that should have suggested to the PNF that, as the PIC, he needed to correct the control inputs and recover from the stall. These included the position of the control column, which was, at times, being held in the full aft position by the PF; continued aerodynamic buffet; the extreme pitch down moments (stall breaks) accompanied by roll-off into steep bank attitudes; engine compressor surges; and the instrument indications of low airspeed and high rate of descent. The Safety Board evaluated why, despite these cues, the PNF did not take control of the airplane or otherwise intervene effectively as the PF held the airplane in a stalled condition all the way to impact.