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RetiredF4 When the aircraft is descending, and you want it to return to the assigned FL, you have to climb. For that you have to raise the nose (SS NU) and maybe you have to add power (TOGA). If 5° pitch is not enough, lets use more........ A rather black comedy of errors, conceived through both a lack of understanding of aircraft dynamics at FL350+ and a poorly constructed and implemented training regime. Not to mention C..R..m.:\ |
Originally Posted by Dozy
How long did you hold it for?
Originally Posted by Dozy
No matter what your personal opinion on autotrim is, the fact is that it did not perform contrary to the way it is supposed to and as such has no place in the report.
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And later on it is possible too, they wanted to arrest the descent. |
Originally Posted by HN39
And what were his targets? Would they have been different in direct law?
The autotrim helped him to believe that the mix of those 2 actions was appropriate as it gave him the temporary illusion of control.
Originally Posted by HN39
If the THS had not moved, the FCS would have commanded more elevator to achieve the demanded response from the airplane, 1.5° for 1° of THS estimated by Owain Glyndwr.
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To the contrary, if the normal operation of a system is a contributory factor in the crash, the report is the very place where that system has to be analyzed. DW will answer (sorry for impersonate) [DW mode open]This was analyzed by BEA and it was determined that it was no contributory to the accident .. So it's no relevant to be in the BEA report [DW mode closed] So I spare DW one post :) |
Originally Posted by studi
At one point, AP will drop-out and the plane will be thrown into the pilots hands totally out of reasonable trim and he will need a lot of force to immediately lower the nose
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First, I have to thank the FBW system we had in the Viper when the LEF folded up just after gear was up. With no input from me the system tried to achieve zero roll rate. Wasn't enough and I added more left stick to stay level. Any airplane at the time would have gone to an uncontrollable right roll and I would have had to pull the handle real quick. So I had a pound or two of roll authority to left, and I then held speed from increasing as I worked out things. Nothing in the books and we didn't even have a simulator yet. I did use the rudder trim to keep the pointy end forward, and I pulled back power to stay at a speed that had allowed me some control. Was I a Chuck Yeager? Well, in that jet at that time we were all "test pilots". We flew more hours in less time than the 5 or 6 years of development, and we had basic hamburgers like me doing things the engineers never thot of.
Tex has it right about THS implementation. Make this clear - I have no problem with the auto trim functionality of the Bus THS. I have no problem with the feature even in any sub-law except "direct". Our auto trim was always back to a trimmed gee that we could set ( can't do that in the Bus). Attitude corrections for the gee trim were not a player, either. I also agree with a few here, that in "direct" law the inherent static stability of the Bus might have helped. In other words, to maintain an attitide you would have to push/pull and the plane would try to achieve some AoA based on cee gee and its basic pitch moment capability of the elevator/THS. Then you trim the sucker. Why this guy thot that 10 or 15 degrees of nose up attitude was acceptable is a mystery. Even in a high-performance jet fighter, those numbers were unacceptable for basic IFR or even VFR cruise. Hell, two or three degrees was about all I ever expected in mild turbulence. |
The drumbeat at the beginning was "do nothing". At a/p drop, that was the first the crew knew something was up. With a roll excursion of four degrees per second, and a bobbing nose, the consensus for another several months was "do nothing". Eventually, and grudgingly, the consensus changed, and people here started to instead assess, "PITCH UP". The a/c needed immediate controls, it was obvious, then in spite of BEA noting "mostly ND inputs" post STALLWARN #1, it was "full back stick, what in the world".....
This thread has some time on it, perhaps eventually the last of the hold outs will let go of "30 other crews survived, what is the big deal?" ICE was never a known fact, from the beginning, it was merely "likely" (BEA). The Autopilot on the A330 has maneuvering limits, and when they are exceeded, it quits, into NORMAL LAW). BEA never took the time to address what may have occurred, except for the "likelihood" of water ICE. This report is a shepherd by default, herding people toward conclusions that must be arrived at independently....there is NO EXCUSE for the foot dragging re: "vitesse douteuse..." whether these Pitots crapped out, or not, NO EXCUSE.... I (we) are in receipt of an enhanced trace of the AUTOTRIM between ap loss and STALL. What does one make of it? "excursions" of less than one degree, with mesas of linger at one second? Shortly after the discussion turned to THS one year ago, takata dropped out.....the drill at the time, was the THS was inhibited, possibly by G...... If the THS was trimming, we could unwind the trace and intuit the SS positions.. Then what do we trust, the SS traces? Or the record of TRIM on the THS trace? If THS, the elevators were deflected to FIVE degrees PITCH? Mystery...... TTex, do you have a theory re: MAYONNAISE? With a rapid movement of the SS can a pilot defeat the AUTOTRIM? Is it an ad hoc method to avoid Autotrim? I simply do not understand why there is the need for this trim when maneuvering, instead of cruising..... |
Originally Posted by studi
Now one can argue that Autotrim is independant from envelope protection. However, to come to a final conclusion about the good or bad of Autotrim, we would need to analyse many more LOC-accidents and recovered LOC-situations, and compare the respective sequences on planes with autotrim and without. Since all of the no-autotrim planes are without protection, it will be hard to make a meaningful conclusion.
Autotrim all the way as long as the data are believed to be reliable. But when the slightest doubt exist, stay humble and reverse straight to direct law - Protections and autotrim can well wait for the next flight.
Originally Posted by studi
I introduced the example of a plane stalled by autopilot (for whatever reason) with no-autotrim. At one point, AP will drop-out and the plane will be thrown into the pilots hands totally out of reasonable trim and he will need a lot of force to immediately lower the nose. Personally I see autotrim in such a situation as very helpful for recovery, and such a scenario has happened too and is in my opinion more likely and more difficult to control than a simple UAS at FL350.
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Originally Posted by Gums
I also agree with a few here, that in "direct" law the inherent static stability of the Bus might have helped. In other words, to maintain an attitide you would have to push/pull and the plane would try to achieve some AoA based on cee gee and its basic pitch moment capability of the elevator/THS. Then you trim the sucker. Why this guy thot that 10 or 15 degrees of nose up attitude was acceptable is a mystery. Even in a high-performance jet fighter, those numbers were unacceptable for basic IFR or even VFR cruise. Hell, two or three degrees was about all I ever expected in mild turbulence.
The more I think about it, the concept of ALT2 Law appears to have a serious logical flaw. It leaves the crew with no AOA/speed related pitch protections and no sense of what speed the aircraft wants to fly at. At least in Direct Law, the aircraft has a speed that it wants to hold. The flight path stability that Alt2 provides can be a serious liability for the inexperienced as well as an aid aid for the competent pilot. In other words, you have less going for you in ALT2 LAW than you do in Direct law. That is anything but graceful degradation of the system.:mad: They ought to call ALT2 law the "You had better be a good stick" Law. |
If I was real particular, this would be my line: wanting a second source of data for the resultant PITCH 447 showed in "the climb", I would suggest utilizing the THS setting On the same time line.
Now the THS trims following the elevators, so until the STALL, the elevators according to THS would be at around five degrees NU. If the computer was in control of the climb, (it was) we would look at another source of record, the sidetick(s). Just because the SS was recorded at various percentages of travel, and appeared to synch with the PITCH, do we know the pilot was using it consistent with the trace record? What does the DFDR record when the aircraft is climbing on its own, relative to the SS movement? Does the SS record a mimic of the Computer's inputs? In Caraibes, what were the SS traces? They were ineffective? Were the actual SS movements recorded, or what they would be if the computer protection was instituting the climb? Using the SS to record elevator position would be counter to design, yes? Wouldn't the elevator positions be recorded? Or the actuators at least? What is the logic for data recording when the climb is out of the pilots control? And why would the SS have any bearing on the AoA anyway, in that event? There are places on the PITCH track that lead the SS movement, by the way. |
Originally Posted by Lyman
If the computer was in control of the climb, (it was) we would look at another source of record, the sidetick(s).
Facts-don't need 'em. I'll make up my own, and my own theory of how fly by wire control works. :ugh: |
.
. [OF's head explodes] . . . |
Threshold effect (in FM)
In other words, you have less going for you in ALT2 LAW than you do in Direct law. That is anything but graceful degradation of the system. They ought to call ALT2 law the "You had better be a good stick" Law. Graceful degradation is like AM (air band VHF, SSB). Accelerated degradation is like FM. Up to a given decaying threshold the Signal to Noise ratio is excellent. Below that, worms invade and... Soft limits x hard limits comes to my mind... No bias against A comparing to B. Just a comment on something important in design concept. |
Originally Posted by CONF iture
Stall warning 2 came just after the FD reappeared. IMO the PF took what he thought to be the correct action by following that reappearing FD, and applied TOGA in response to the stall warning.
Moreover, the flight director displays could have prompted him to command a positive pitch angle, of about 12.5°. This value appears in the stall warning procedure for the take-off phase. It is possible that, even though he did not call it out, the PF had recalled this memorised value and then had clung to this reference without remembering that it was intended for a different flight phase. The conjunction of this remembered value and the flight director displays may have constituted one of the few (and maybe even the only) points of consistency in his general incomprehension of the situation. Thus, it seems likely that the flight director exerted an influence.
Originally Posted by CONF iture
The autotrim helped him to believe that the mix of those 2 actions was appropriate as it gave him the temporary illusion of control.
Originally Posted by CONF iture
I'm not to sure about that equation or how to interpret it, would it mean that a full deflection of the THS at minus 14 deg could be anihiled by 21 deg down of elevators ?
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Originally Posted by Lyman
ICE was never a known fact, from the beginning, it was merely "likely" (BEA).
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Ice impact was audible on cvr.
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Originally Posted by HN39
The final report, HF part, section 2.1.3.3.1 is not quite so positive
Also if the PF was really minded to go for 12.5 or 15 or any other precise attitude, he would have most probably deselect the FD as they become a nuisance to his concentration.
Originally Posted by HN39
The motion of the THS does not change the response of the airplane to the PF's inputs. He could not have perceived it except by monitoring the trim wheel or the EIS, which seems unlikely. Until about 02:11:40 autotrim had no effect on the airplane's motion nor on the pilot's perception of it.
It was far too easy to develop the stall. As a side note, no explanation has been given why the THS did not reach the 14 deg limit ? |
The drumbeat at the beginning was "do nothing". At a/p drop, that was the first the crew knew something was up. With a roll excursion of four degrees per second, and a bobbing nose, the consensus for another several months was "do nothing". Eventually, and grudgingly, the consensus changed, and people here started to instead assess, "PITCH UP". The a/c needed immediate controls, it was obvious, then in spite of BEA noting "mostly ND inputs" post STALLWARN #1, it was "full back stick, what in the world"..... This thread has some time on it, perhaps eventually the last of the hold outs will let go of "30 other crews survived, what is the big deal?" ICE was never a known fact, from the beginning, it was merely "likely" (BEA). The Autopilot on the A330 has maneuvering limits, and when they are exceeded, it quits, into NORMAL LAW). BEA never took the time to address what may have occurred, except for the "likelihood" of water ICE. This report is a shepherd by default, herding people toward conclusions that must be arrived at independently....there is NO EXCUSE for the foot dragging re: "vitesse douteuse..." whether these Pitots crapped out, or not, NO EXCUSE.... Must be time to start over from the beginning (rerun): Introduction to Chapter 1 (A): There is a problem. A small but positive attitude, yes, but don't forget that there was said to be a yawing moment, sufficient to fail the VS at impact, and in a leftward direction. The BEA make a great deal of there being no aerodynamic loading to cause the separation of the Vertical in flight, and I think their term was "Struck the water En Ligne de Vol", (direction of flight). This means to me no yaw whatsoever at impact. So it seems to me someone is letting the authority have it both ways. The Stabilizer stayed with the a/c, "what a stout airframe". It rotated off at impact even though the tail was following the nose "En Ligne"? Did it rotate forward around the #1 Clevis? Two things are missing, as I see it. Metallurgy/Composite autopsy. Passenger autopsies as to injuries. One cannot learn from less than forthcoming analysis. |
As a side note, no explanation has been given why the THS did not reach the 14 deg limit ? I don't know if this is true for the Airbus since there is no electric 'trim switch' as such to run the trim to its electric stops to see where they are. IIRC I think at relatively forward CG's you might temporarily see max nose up autotrim positions of around 11 degrees during deceleration as you initially configured the aircraft for approach....well inside the 13 degree setting. If you extend the slats below 20,000 very near or in the stall, IIRC 11 degrees is about where you initially end up, prior to acceleration. It's a good question. (Thanks to PJ for the THS info.) |
Originally Posted by CONF iture
To the contrary, the motion of the THS (most probably unoticed) makes all the difference between forcing on the stick or not.
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Re : ACARS printer position
Thank you, PJ2 and EMIT for respective picture and information.
You confirm the ACARS printer was just before the eyes of Marc DUBOIS when he came back in the cockpit... the first thing he could see ! |
@rh:
Why would an airline captain, clearly arriving in the middle of an emergency, immediately go to the maintenance log printer and read the output? |
rh;
You confirm the ACARS printer was just before the eyes of Marc DUBOIS when he came back in the cockpit... the first thing he could see ! |
Originally Posted by HN39
Would you care to explain that? Difference in stickforce vs stick angle? Different airplane response to stick angle?
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CONF iture,
I don't see the relevance of (1) and (2) for the AF447 scenario. IMO 1/5 of the full SS deflection demands a certain level of 'g' and the FCS will provide that irrespective of the THS position, as long it it doesn't need more than full elevator. |
Hazelnuts39
You seem to be falling into the simplistic trap of assuming the elevators and THS were behaving normally. They weren't. The airflow around them approximated to an M2-F1 flight more than anything. Autotrim should have been disengaged as soon as there was a disagree, because it has to be protected in different ways for different flight regimes. If the flight system doesn't know where it is (alt, speed) then it cannot protect the THS rate and the THS will run away too far too fast, as it did, making the airplane unflyable. Not for the first time, either. I am not a pilot and have no qualification beyond a vaguely relevant degree. I never fly. |
Studi But that is a non-issue for me, as in alternate mode, the Airbus still protects you somehow, which is more than any conventional plane. For me any protection is better than no protection, as long as it does not wrongly protect. I think we can agree on that. But would you please explain the bolding in the above sentence some more, especially with regard to AF447, as we are discussing that accident here? To be specific, autothrust is no protection in the sense of discussion here, and autotrim is just a feature to relieve the pilot of trimming without any force feedback under impementation of NZ law. I know there is load factor protection left, but others than that? |
mike-wsm,
your understanding of the A330 flight controls is obviously different from mine. As I said, the THS position is important when the elevator is used to its maximum capacity. Otherwise it doesn't matter at all. |
Originally Posted by HN39
I don't see the relevance of (1) and (2) for the AF447 scenario.
Originally Posted by HN39
IMO 1/5 of the full SS deflection demands a certain level of 'g' and the FCS will provide that irrespective of the THS position, as long it it doesn't need more than full elevator.
No autotrim and it won't be 1/5 but anything up to full stick deflection in the target pursuit. The BEA is not saying anything different except that for those 2 key paragraphs they avoid mentioning the word autotrim and they should have added to the end of the second one : "It appears that this absence of positive static stability could have contributed to the PF not identifying the approach to stall and the aggravation of the stall."
Originally Posted by Final Report P187 en
When there are no protections left, the aeroplane no longer possesses positive longitudinal static stability even on approach to stall. This absence specifically results in the fact that it is not necessary to make or increase a nose-up input to compensate for a loss of speed while maintaining aeroplane altitude. This behaviour, even if it may appear contrary to some provisions in the basic regulations, was judged to be acceptable by the certification authorities by taking into account special conditions and interpretation material. Indeed, the presence of flight envelope protections makes neutral longitudinal static stability acceptable.
However, positive longitudinal static stability on an aeroplane can be useful since it allows the pilot to have a sensory return (via the position of the stick) on the situation of his aeroplane in terms of speed in relation to its point of equilibrium (trim) at constant thrust. Specifically, the approach to stall on a classic aeroplane is always associated with a more or less pronounced nose-up input. This is not the case on the A330 in alternate law. The specific consequence is that in this control law the aeroplane, placed in a configuration where the thrust is not sufficient to maintain speed on the flight path, would end up by stalling without any inputs on the sidestick. It appears that this absence of positive static stability could have contributed to the PF not identifying the approach to stall. |
But CONF, you're basing that assertion on a supposed sim experience you had where you could not get the nose back down. My sim experience (as well as other people's) seems to suggest differently.
You can't deny that you're less interested in safety than sticking one to Airbus and always have been. |
Originally Posted by Dozy
But CONF, you're basing that assertion on a supposed sim experience you had where you could not get the nose back down. My sim experience (as well as other people's) seems to suggest differently.
Originally Posted by Dozy
You can't deny that you're less interested in safety than sticking one to Airbus and always have been.
Originally Posted by Dozy
This is one of the reasons I get extremely vexed when I'm accused of "defending" Airbus.
But definitely you are a funny guy Dozy. |
Originally Posted by CONF iture
You are the one asking the ''difference in stickforce vs stick angle'' I just provide the exemple.
How will you get that certain level of 'g' if the autotrim does not cooperate but by pulling more on the stick ? No autotrim and it won't be 1/5 but anything up to full stick deflection in the target pursuit. When the BEA note the absence of positive static stability in the Nz law, and how that may have affected the pilot's perception, it is not about autotrim because that is irrelevant in that context. EDIT:: The Nz law can be used in an airplane like the F-16 with an all-flying-tail, or theoretically with a non-trimmable stabilizer. |
Picking on DW again
But CONF, you're basing that assertion on a supposed sim experience you had where you could not get the nose back down. You can't deny that you're less interested in safety than sticking one to Airbus and always have been. |
HN
My question was how the THS affects the stickforce vs stick angle. You wrote: "Displacing the sidestick is like fighting a spring, the further you go the heavier it becomes." That is correct, and doesn't change due to THS movement. I will need some clarification of that statement? Because the effect of the elevators can be extremely different on the airframe, depending on the Pitch of the HS. |
Studi Now what do it mean with alternate law protects you somehow. Depending on the failure, Alternate Law has not only load factor protection, but also high and low speed stability. Low speed stability induces a nose down moment if you get too slow, however can be overriden with the stick (not possible in normal law). Same with high speed stability. However, in daily ops, I don't need to know that I have it, as I am not supposed to use it deliberately. If it helps me, fine, that is my advantage, if not, I am as bad as in a conventional plane. Maybe i should have quoted the whole sentence of you. (bolding by me) That is why it leaves normal law and enters alternate law, and that is why alternate law has in itself different levels of protection. But that is a non-issue for me, as in alternate mode, the Airbus still protects you somehow |
Lyman,
The stickforce characteristic is shown here. The loadfactor versus SS deflection is shown here. The point is that to hold the stick at 20% of full travel requires a certain force, and that 20% deflection of the SS commands a certain loadfactor, whatever the THS position is. If you have any more questions, please be more specific. |
Why the crew couldn't solve the problem?
Earlier on in this thread one poster said
"Sadly, the (non adequately trained) crew of AF447 were:-: Surprised by the System output and worse: Had to process garbage generated by the System. And failed in their decision making. Actually, worse than that, never realizing (in time) what was going on..."There has to be some reason for this. OK, some of the crew might have been relatively inexperienced or under-trained but they certainly weren't stupid. They were bright, skilled and well-qualified. Yet somehow they just couldn't get their heads around what was happening to their aircraft .Could their thinking-power have been impaired by breathing insufficient oxygen?. Has anyone even bothered asked the question?.(.Exactly the point I was trying to make in the “SLF” thread "Can Pilots REALLY concentrate at 35,000 feet?". We know that none of the crew of AF447 had done what they really needed to do - don oxygen masks. Their blood oxygen levels after four hours at 35,000 feet would have been severely depleted. They wouldn’t have been aware of it. Most pilots aren’t. They could still perform the mundane routine stuff just fine - most crews can. But in all probability is was simple lack of oxygen that prevented them from firing up the extra brainpower they desperately needed to get them out of the aeronautical elephant-trap they were falling into. Chief investigator Alain Bouillard says that the pilots simply needed to “properly react” to in-flight circumstances. “When it comes down to it, safety will always be based on the capacity of the pilots and the signals which they are given, which they have to understand and react to,” he said. He’s right - but if you feed pilots air at a cabin altitude of 8000 feet (much lower in oxygen content than air at a real altitude of 8000 feet) then when the chips are down crews will make mistakes - and they did. |
Korrel
OK, some of the crew might have been relatively inexperienced or under-trained but they certainly weren't stupid. They were bright, skilled etc I don't think the training records of the two F/O's are in the public domain. We know that none of the crew of AF447 had done what they really needed to do - don oxygen masks. Their blood oxygen levels after four hours at 35,000 feet would have been severely depleted I've been sat there at 33000 ft and lost the 'cabin' - then I put on the oxygen mask and decended. Korrel, with all due respect, I think you have failed to notice one or more 'elephants in the room'. |
He’s right - but if you feed pilots air at a cabin altitude of 8000 feet (much lower in oxygen content than air at a real altitude of 8000 feet) then when the chips are down crews will make mistakes - and they did. |
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