AF 447 Thread No. 5
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Bearfoil,
The fundamental issue is that the PF applied mostly nose-up inputs - hence the THS progressively trimmed up (by integrating his input).
If he had applied the correct stick-forward action in response to a stall, we wouldn't be talking about this at all. The design of the auto-trim is not the cause - the THS acted in response to the PF's input. His inputs were not appropriate. Cause and effect.
In fact, if he had flown pitch and power, it wouldn't have stalled at all.
The fundamental issue is that the PF applied mostly nose-up inputs - hence the THS progressively trimmed up (by integrating his input).
If he had applied the correct stick-forward action in response to a stall, we wouldn't be talking about this at all. The design of the auto-trim is not the cause - the THS acted in response to the PF's input. His inputs were not appropriate. Cause and effect.
In fact, if he had flown pitch and power, it wouldn't have stalled at all.
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In fact, if he had flown pitch and power, it wouldn't have stalled at all.
but what about tactile (pitch) feedback?
Shouldn't a multi-million dollar airliner have a stalled feeling at 100 knots or less?
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sdf666
It is the initial handoff that killed this plane, imo. I think that, for whatever reason, the PF wanted to climb, and may have not anticipated a lock out of the Autotrim with a robust Pitch UP. So he kept increasing input (NU), and the a/c started to climb, which lessened g forces, and started the THS TRIMMING NU. This caused a very emphatic PITCH UP, one he addressed with insufficient NOSE DOWN ELEVATOR to reverse the climb angle. In short, because (possibly) he had expected some kind of NL assistance with his pull, and getting none, he kept pulling. When it took hold, he lost his surroundings (SA) possibly, and never caught up with, nor understood, the UPSET handling of his a/c.
I am convinced that some variation of this is what started the problem. What cause dit to be ultimately insoluble is left to others.
Sufficient lack of initial SA, a correct, (though perhaps forgotten) behaviour of the THS, and the rest is coffee table.
Thanks for your response. Finally, look again at your initial statement, separate the sequence of both points, and voila! The initial 'disconnect'
IOW. The THS was NOT TRIMMING up with his first NU inputs. K?
It is the initial handoff that killed this plane, imo. I think that, for whatever reason, the PF wanted to climb, and may have not anticipated a lock out of the Autotrim with a robust Pitch UP. So he kept increasing input (NU), and the a/c started to climb, which lessened g forces, and started the THS TRIMMING NU. This caused a very emphatic PITCH UP, one he addressed with insufficient NOSE DOWN ELEVATOR to reverse the climb angle. In short, because (possibly) he had expected some kind of NL assistance with his pull, and getting none, he kept pulling. When it took hold, he lost his surroundings (SA) possibly, and never caught up with, nor understood, the UPSET handling of his a/c.
I am convinced that some variation of this is what started the problem. What cause dit to be ultimately insoluble is left to others.
Sufficient lack of initial SA, a correct, (though perhaps forgotten) behaviour of the THS, and the rest is coffee table.
Thanks for your response. Finally, look again at your initial statement, separate the sequence of both points, and voila! The initial 'disconnect'
IOW. The THS was NOT TRIMMING up with his first NU inputs. K?
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takata
We are a committee. One is a writer, an editor, actually. A retired Pilot, an active PPL, and others, a designer, a mechanic, etc.
If this is illegal, then we say adieu.
If not, when you gather your thoughts, can you respond? You brought it up. The THS is dormant to help in the NU demand. Later, with a climb initiated, it activates and zooms the a/c.
We are a committee. One is a writer, an editor, actually. A retired Pilot, an active PPL, and others, a designer, a mechanic, etc.
If this is illegal, then we say adieu.
If not, when you gather your thoughts, can you respond? You brought it up. The THS is dormant to help in the NU demand. Later, with a climb initiated, it activates and zooms the a/c.
C* control law is no mystery, it is a feedback control loop that moves the control surfaces to achieve the demanded movement (by g-load). Autotrim is no mystery either - THS follows elevator to unload it, slowly and with some hysteresis.
At the start of the incident, at cruise speed and alt, the elevator movement required to achieve the demanded climb was small, and the THS moved little or not at all to compensate because it didn't need to. The THS never zoomed the a/c - it started moving only after the zoom climb.
As airspeed bleeds off the control deflection required to achieve the demanded "climb" increases, and as the plane stalls the controls are trying to achieve the aerodynamically impossible - the elevator hits the stops and the THS follows. In the stall. In the stall, because that is what it is being asked to do. The basic control laws have no concept of "stall", just like previous generations of cables and hydraulics - and nor should they, it is far too complex a concept to attempt to build into such low level critical systems.
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Hey. Absolutely, and in a perfect world. This a/c did not immediately respond to climb input, in spite of cruise speed and controls effectiveness. So, we are left with a need to explain the sluggish response of a highly vaunted "Twitchy" platform. Evidently not? A sluggishness replaced with a near instantaneous and remarkable need for Altitude? After handoff, Throttles were not touched, and the a/c loitered at 34,700 (Read)?
My point is that no one has sufficiently put together a logical continuum of the initial UPSET. There is perpetual reiteration of everything but.
TAG. You're IT.
And of course, you know the diff twixt UPSET and LOC?
My point is that no one has sufficiently put together a logical continuum of the initial UPSET. There is perpetual reiteration of everything but.
TAG. You're IT.
And of course, you know the diff twixt UPSET and LOC?
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the PF wanted to climb, and may have not anticipated a lock out of the Autotrim with a robust Pitch UP. So he kept increasing input (NU), and the a/c started to climb
[...]
I am convinced that some variation of this is what started the problem. What cause dit to be ultimately insoluble is left to others.
[...]
I am convinced that some variation of this is what started the problem. What cause dit to be ultimately insoluble is left to others.
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Originally posted by DozyWannabe
Personally I think that the logic for not re-taking a seat at the controls was understandable. What bothers me is the fact that he felt it OK to leave two F/O's, one of whom was fairly junior and probably still a little demob-happy (having just returned from vacation) in charge as the aircraft was transiting a known problem weather area.
Personally I think that the logic for not re-taking a seat at the controls was understandable. What bothers me is the fact that he felt it OK to leave two F/O's, one of whom was fairly junior and probably still a little demob-happy (having just returned from vacation) in charge as the aircraft was transiting a known problem weather area.
Another thing which bothers me is the fact, that the captain asked his co-pilot if he had a licence just bevor he went to rest......... means quite well advanced with their flight.
Is it not normal bevor departure that the team gets at least acquainted and the commander clears important questions like that, bevor boarding?
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A while ago I posed the question "In a FBW Airbus how would you sense which way to trim?" to smilin-ed and the answers generated show that many posters don't understand the system.
To answer my own question: "The only sense which can solve the problem is sight - look at the ECAM F/CTL page. If the elevator is neutral with sidestick released the a/c is in trim. If the elevator is displaced then trim in the same direction until elevator is neutral. This will only work with 1g demanded i.e. no sidestick deflection in pitch."
The point I wish to make to smilin-ed is that you cannot feel if the a/c in in trim (except in Direct Law). Autotrim was not the reason for this accident.
To answer my own question: "The only sense which can solve the problem is sight - look at the ECAM F/CTL page. If the elevator is neutral with sidestick released the a/c is in trim. If the elevator is displaced then trim in the same direction until elevator is neutral. This will only work with 1g demanded i.e. no sidestick deflection in pitch."
The point I wish to make to smilin-ed is that you cannot feel if the a/c in in trim (except in Direct Law). Autotrim was not the reason for this accident.
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For example, in the case of one of the best examples of CRM there has ever been (the crash of United Airlines 232 at Sioux City), none of the crew had been personally introduced to Captain Denny Fitch - who was a DC-10 training captain who was "deadheading" on the flight - ever before. But what you hear on that CVR is the trust that all the flight crew, plus their new member, have in each other and the decisions that meant that a lot of people walked away from a crash that was likely to have killed everyone on that aircraft. What I'm trying to say is that in the airline environment, it's a regular occurrence that you'll be working with people that you haven't worked with before - that's not unusual.
Unfortunately, what we're looking at here appears to be at the other end of the scale - a Captain who puts his faith in his two F/Os to manage that leg of the flight, but when things start going wrong it is apparent that at least one of the F/Os (in the right-hand seat) is not handling the situation correctly, and the other F/O (in the left-hand seat) doesn't feel that he has the authority to take over when something goes wrong and waits for the Captain to return, by which time it is effectively too late.
Wuenschen wir doch, als unser Piloten alles klar verstehen koennen.
Tyro:
Tyro, I am well aware the truth in both of these statements. My points are:
1.In my opinion, not having any change in the feeling of the side stick as flight conditions change makes it harder to trim properly. Some people seem to think otherwise, but that is their opinion. This, however is not even a contributing cause of this accident.
2. Autotrim did not cause the accident since the person flying did not even try to recover from the stall which he caused by his persistent nose up inputs. However, if he had tried to recover from the stall it would have been more difficult because autotrim caused the THS to move to the full nose up position. It would have taken more time to attain a nose-down pitching moment than if trim had stayed at the cruise setting.
The point I wish to make to smilin-ed is that you cannot feel if the a/c in in trim (except in Direct Law). Autotrim was not the reason for this accident.
1.In my opinion, not having any change in the feeling of the side stick as flight conditions change makes it harder to trim properly. Some people seem to think otherwise, but that is their opinion. This, however is not even a contributing cause of this accident.
2. Autotrim did not cause the accident since the person flying did not even try to recover from the stall which he caused by his persistent nose up inputs. However, if he had tried to recover from the stall it would have been more difficult because autotrim caused the THS to move to the full nose up position. It would have taken more time to attain a nose-down pitching moment than if trim had stayed at the cruise setting.
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Smilin_Ed keeps making crushing points from the point of view of a real pilot with his human cargo in tow, well aware of how to ensure their safety to the best of his considerable skill. It makes me happy There are still real pilots around, with pride and skill in their craft.
There are still real pilots around, with pride and skill in their craft.
Look at the report. The trim does nothing until the a/c is at top of climb and proabbly already stalled. It does nothing because it didn't have to - small elevator movement was enough. Only as it becomes increasingly difficult to maintain the (impossible) climb does the elevator start to move significantly NU and the THS follow. There was no lockout of autotrim. Look at the traces.
The obsession with the THS and autotrim is becoming tedious - the THS did what it was told to do, according to the design of the aircraft. The millions of miles covered by the A330 platform presumably are a reasonable certification of the designs basic soundness - let alone the other Airbus aircraft types of basically identical design.
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Looking toward the future, how much nose up trim do you really need at FL350?
Are you ever going to drop the flaps up there?
Maybe the control laws need to be looked at in this regard.
Shouldn't some limiting AOA shut down nose up autotrim in Alt law before it gets really ridiculous?
I hate the thought of limiting control authority in some corners of the envelope, but it seems we are moving in a direction where future pilots will need yet more coddling.
Are you ever going to drop the flaps up there?
Maybe the control laws need to be looked at in this regard.
Shouldn't some limiting AOA shut down nose up autotrim in Alt law before it gets really ridiculous?
I hate the thought of limiting control authority in some corners of the envelope, but it seems we are moving in a direction where future pilots will need yet more coddling.
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Bear is in Alaska, visiting his Polar cousins.
Machinbird, that is a strong point to make. Not new, but strong. Airbus has installed a Trimming system for its elevators (strictly, for the a/c Pitch). There is a reason, a good one. The elevators are a part of a balanced system of demand, and managed stress. As you say, why such an exaggerated system? Possibly, with un"limited" authority, the elevators are subject to large air loads. A movable Stabiliser spreads this stress away from the smaller controls, the elevators.
So why the need for such large excursions in control surface? Why indeed.
Certainly not for authority? At cruise, the deflections are necessarily small, and actually create a danger of damage if they are too large. For added control at Approach to Stall?
The RTLU? Ever more important than the Rudder are the elevators. Yet there is no protection at high Mach for these critical surfaces (els)? As has been mentioned many times since AA587, a Rudder can be lost and the flight saved. A vertical Stabiliser if lost is the end of times.
Is the THS indeed a separate approach for control surface protection at high Mach? Then why not fly TRIM? Lock the elevators (a la RTLU), and use the slab to control Pitch. With a dampened and restricted stick at Mach, there will be no Mayonnaise. Likewise ROLL. How can it be so that this dream machine can wobble right and left, inviting a spin, due to PILOT? Especially with such rapid moves?
Always look in the corners, and bring a torch. This investigation has no conclusions as yet. Save those of the Armchair jocks here, evidently.
And those based on nothing more than prejudice and Pride.
Machinbird, the trend is toward more tech, and less pilotage. Shouldn't AB be more attentive to the different "requirements" of the cockpit, and its protections? Is that the question? In the interests of safety and pragmatism, yes of course.
To get defensive (and derisive) not to mention dismissive of decent questions is not only amateurish, it is lazy, even sloppy.
Machinbird, that is a strong point to make. Not new, but strong. Airbus has installed a Trimming system for its elevators (strictly, for the a/c Pitch). There is a reason, a good one. The elevators are a part of a balanced system of demand, and managed stress. As you say, why such an exaggerated system? Possibly, with un"limited" authority, the elevators are subject to large air loads. A movable Stabiliser spreads this stress away from the smaller controls, the elevators.
So why the need for such large excursions in control surface? Why indeed.
Certainly not for authority? At cruise, the deflections are necessarily small, and actually create a danger of damage if they are too large. For added control at Approach to Stall?
The RTLU? Ever more important than the Rudder are the elevators. Yet there is no protection at high Mach for these critical surfaces (els)? As has been mentioned many times since AA587, a Rudder can be lost and the flight saved. A vertical Stabiliser if lost is the end of times.
Is the THS indeed a separate approach for control surface protection at high Mach? Then why not fly TRIM? Lock the elevators (a la RTLU), and use the slab to control Pitch. With a dampened and restricted stick at Mach, there will be no Mayonnaise. Likewise ROLL. How can it be so that this dream machine can wobble right and left, inviting a spin, due to PILOT? Especially with such rapid moves?
Always look in the corners, and bring a torch. This investigation has no conclusions as yet. Save those of the Armchair jocks here, evidently.
And those based on nothing more than prejudice and Pride.
Machinbird, the trend is toward more tech, and less pilotage. Shouldn't AB be more attentive to the different "requirements" of the cockpit, and its protections? Is that the question? In the interests of safety and pragmatism, yes of course.
To get defensive (and derisive) not to mention dismissive of decent questions is not only amateurish, it is lazy, even sloppy.
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Looking toward the future?? What future? Who needs people? They pay taxes, but you have to feed them. Zero sum game.
I always thought pilots were a cut above, and it still may be so, and what I'm seeing is only the cross-section of the mediocre who bother with forums. I'd hate to think that this is it, in these forums, 3 or 4 real pilots plus a bunch of bull****ters, but it may be so.
I always thought pilots were a cut above, and it still may be so, and what I'm seeing is only the cross-section of the mediocre who bother with forums. I'd hate to think that this is it, in these forums, 3 or 4 real pilots plus a bunch of bull****ters, but it may be so.
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Maybe this set of graphs can help a number of points made or questions asked in several posts during this past week or two:
Stall Warning Active and THS Nose UP, from -3 to -13 degrees (max) during the same time interval - see the Gray Area.
Stall Warning Active and THS Nose UP, from -3 to -13 degrees (max) during the same time interval - see the Gray Area.
Looking toward the future, how much nose up trim do you really need at FL350?
Are you ever going to drop the flaps up there?
Maybe the control laws need to be looked at in this regard.
Shouldn't some limiting AOA shut down nose up autotrim in Alt law before it gets really ridiculous?
Are you ever going to drop the flaps up there?
Maybe the control laws need to be looked at in this regard.
Shouldn't some limiting AOA shut down nose up autotrim in Alt law before it gets really ridiculous?
Last edited by airtren; 11th Aug 2011 at 04:02.
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airtren
Perhaps a narrative? In the gray? Because I'm seeing a dogleg at the ELEVATORS/THS Hinge axis. Maybe it's just late.....
How did the aircraft get to be so out of shape with the elevators and THS at virtually the same deflection as where the A/P had them? It Stalled with max Elevator position +/- 2 degrees? And the THS parked at -3 til 2:10:51? Looking for the Dunce cap.......
Perhaps a narrative? In the gray? Because I'm seeing a dogleg at the ELEVATORS/THS Hinge axis. Maybe it's just late.....
How did the aircraft get to be so out of shape with the elevators and THS at virtually the same deflection as where the A/P had them? It Stalled with max Elevator position +/- 2 degrees? And the THS parked at -3 til 2:10:51? Looking for the Dunce cap.......