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AF 447 Thread No. 9

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AF 447 Thread No. 9

Old 15th Aug 2012, 20:12
  #1321 (permalink)  
 
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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........
.... and when the FD bars reappear; lets chase them!

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.
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Old 15th Aug 2012, 20:55
  #1322 (permalink)  
 
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Originally Posted by Dozy
How long did you hold it for?
Long enough to confirm that the attitude would not decrease.

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.
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.
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Old 15th Aug 2012, 20:57
  #1323 (permalink)  
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And later on it is possible too, they wanted to arrest the descent.
Yes, very possible, as a "fright" response - the Airborne Express DC8 accident F/O exhibited the same behaviour. Sad.
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Old 15th Aug 2012, 22:04
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Originally Posted by HN39
And what were his targets? Would they have been different in direct law?
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.
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.
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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Old 15th Aug 2012, 22:08
  #1325 (permalink)  
 
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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.
Useless ..
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

Last edited by jcjeant; 15th Aug 2012 at 22:09.
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Old 16th Aug 2012, 00:43
  #1326 (permalink)  
 
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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
If in such an airplane, the trim stops when AP drops out. The pilot is presented with normal handling. Normal stick force per knot away from trim speed feel exists. Yes, he will need a lot of force to lower the nose, but more importantly, he will need a significantly larger amount of PULL force to further reduce speed/increase angle of attack. Assuming of course that your example airplane offers control force feedback to the pilots hands.
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Old 16th Aug 2012, 01:23
  #1327 (permalink)  
 
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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.

Last edited by Jetdriver; 16th Aug 2012 at 11:11.
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Old 16th Aug 2012, 01:31
  #1328 (permalink)  
 
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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.....
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Old 16th Aug 2012, 02:11
  #1329 (permalink)  
 
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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.
Such debate is not the right one.
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.
You did mention a few times AMS, but I am not sure you fully grab the complexity behind the erroneous data and what could be the possible consequences for the Airbus scenario ...
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Old 16th Aug 2012, 02:13
  #1330 (permalink)  
 
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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.
Hi Gums.
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. They ought to call ALT2 law the "You had better be a good stick" Law.
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Old 16th Aug 2012, 02:36
  #1331 (permalink)  
 
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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.
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Old 16th Aug 2012, 05:16
  #1332 (permalink)  
 
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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).
You are beginning to sound like a conspiracy theorist. Or is the proper gerund the word 'continuing'?

Facts-don't need 'em. I'll make up my own, and my own theory of how fly by wire control works.
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Old 16th Aug 2012, 05:54
  #1333 (permalink)  
 
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.
.

[OF's head explodes]
.
.
.
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Old 16th Aug 2012, 06:02
  #1334 (permalink)  
 
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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.
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Old 16th Aug 2012, 07:42
  #1335 (permalink)  
 
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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.
The final report, HF part, section 2.1.3.3.1 is not quite so positive:
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.
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.
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 ?
Yes, that's what it means. Owain Glyndwr explained and applied it in his post. Let's not quibble about the exact value of the exchange rate. The important point is that THS and elevator are interchangeable, until either one reaches its limit.

Last edited by HazelNuts39; 16th Aug 2012 at 12:50. Reason: expanded reply to post
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Old 16th Aug 2012, 07:46
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Originally Posted by Lyman
ICE was never a known fact, from the beginning, it was merely "likely" (BEA).
The crew said they were entering cloud. At -40C cloud is air filled with ice particles.
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Old 16th Aug 2012, 12:25
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Ice impact was audible on cvr.
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Old 16th Aug 2012, 14:43
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Originally Posted by HN39
The final report, HF part, section 2.1.3.3.1 is not quite so positive
Some stuff cannot be positively affirmed in a report, as the only guy who could confirm cannot be interviewed anymore. But the logic is here, and if you listen to Mr Traodec during the press conference, doubt there is not much.
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.
To the contrary, the motion of the THS (most probably unoticed) makes all the difference between forcing on the stick or not.
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 ?
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Old 16th Aug 2012, 15:10
  #1339 (permalink)  
 
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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....
This has got to be the last chapter in the technical series "Theories of FBW Aircraft Operations From A to Z". (sigh)...

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.
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Old 16th Aug 2012, 15:40
  #1340 (permalink)  
 
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As a side note, no explanation has been given why the THS did not reach the 14 deg limit ?
The Boeings have an electric stop a degree or so prior to full travel, from which the trim limits can only be reached by rotating the trim wheel manually.

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.)
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