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AF 447 Thread No. 9

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AF 447 Thread No. 9

Old 20th Aug 2012, 14:50
  #1441 (permalink)  
 
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"May be a re-thinking of the trigger values for abnormal attitude law would be interesting, as it was never triggered in AF447".

Which is odd, since it's trigger(s) was exceeded seven miles up.......

Autotrim, and faulty Abnormal logic, what's a mother to do?
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Old 20th Aug 2012, 16:05
  #1442 (permalink)  
 
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Abnormal attitude law was not triggered not because of a "wrong" (i.e. too low or too high) trigger value, but because the ADR were rejected i.e. whatever values they gave were ignored.

I'm not sure trying to "solve" this "issue" is the best path to follow.

[edit] Not sure to be clear, so let's try to do better:
I don't think values of a rejected ADR (<= with good reason) should be taken into account.
OTOH, rejecting an ADR "as a whole" is perhaps too much: AoA and pitot probes have different physical characteristics, meaning different behavior in adverses conditions.

Last edited by AlphaZuluRomeo; 20th Aug 2012 at 16:10.
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Old 20th Aug 2012, 16:57
  #1443 (permalink)  
 
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Abnormal Attitude ....


Mr Christian Roger send me a answer to me about .....

It is true that if the FDR marks the passage into law alternate to 02h 10
06, there is no trace of a passage into law unusual attitudes

But this is an anomaly, because according to the documentation Airbus therefore
the incidence reached 30 ° 02h 11 33, this Act shall come into
force. I have found nowhere confirmation of statements
BEA on the need for 3 ADR that this law works. and I
indicates that at that time the FD are in operation and therefore at least
2 ADR are too. It should be noted also that I have not
mentioned that Airbus is the logic, which means that if you have three systems,
is removed the data that is not in phase with the two
other .............. even if it is one that is good!
Il est exact que si le FDR signale le passage en loi alternate à 02h 10
06, on ne trouve pas trace d'un passage en loi attitudes inusuelles

Mais c'est là une anomalie, car selon la documentation Airbus, dès lors
que l'incidence atteint 30°à 02h 11 33, cette loi doit entrer en
vigueur. Je n'ai trouvé nulle part la confirmation des affirmations du
BEA sur la nécessité de 3 ADR pour que cette loi fonctionne. Et je
signale qu'à ce moment là les FD sont en fonctionnement et donc au moins
2 ADR le sont aussi. Il faut signaler aussi un point que je n'ai pas
évoqué qui est la logique Airbus, qui veut que si on a trois systèmes,
on élimine la donnée qui n'est pas en phase avec les deux
autres..............même si c'est celle qui est la bonne !

Last edited by jcjeant; 20th Aug 2012 at 16:58.
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Old 20th Aug 2012, 17:01
  #1444 (permalink)  
 
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...but HN39 showed that as long as the elevators are not full nose-up, this wouldn't change anything.
AZR:

May I just say one more thing about this so I don't mislead anyone who
actually does this for a living.

HN39 is entirely correct 'theoretically'...

but in the current embodiment of Alternate Law, when a THS 'jam' (STAB CTL FAULT) is in effect from either holding the trim wheel or inserting the failure, you will also eventually see triple PRIM PITCH faults.

Under circumstances where the Stab is available, triple PRIM faults put you in Direct Law and advises to Use Manual Pitch Trim.

If the condition is entered as a result of the THS fault, you also effectively end up in Direct Law when the PRIMS fault as a result of the Stab 'jam'. However no message to Use Manual Pitch Trim appears, for obvious reasons.

From this point, as speed changes, the pilot has to make SS inputs to maintain a given flightpath, as opposed to Alternate Law WITH autotrim where the flightpath can be maintained 'hands off'. Manual SS inputs generally do not produce the precise flight path control that automated inputs do.

(Whether or not the stall would have developed in either case or have been less likely with a fixed THS is entirely speculative and a matter of opinion.)

That is the difference.

Last edited by OK465; 20th Aug 2012 at 17:11. Reason: italics
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Old 20th Aug 2012, 19:02
  #1445 (permalink)  
 
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Enough of your broad brush shoot the messenger drill...

Lyman takes a hit, does that make Airbus and BEA "collateral damage"?


"But this is an anomaly, because according to the documentation Airbus therefore
the incidence reached 30 ° 02h 11 33, this Act shall come into
force. I have found nowhere confirmation of statements
BEA on the need for 3 ADR that this law works. and I
indicates that at that time the FD are in operation and therefore at least two ADR are too..."


Take a breath

My question would be, since three ADR were not failed throughout, why would AL2 obtain continuously? Especially when AoA jumped past 30 degrees.

After qualifying criteria have sorted, why remain in this rare form? Why Autotrim remains active with SW and STALL exceeded? Why it stays at full NU throughout? This aircraft is not only possessed of some odd logic, IMO, but some rather dangerous and stubborn illogic.

Last edited by Lyman; 20th Aug 2012 at 19:12. Reason: Remove rude word....
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Old 20th Aug 2012, 19:31
  #1446 (permalink)  
 
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If for UAS the drill is to switch FD off then as the system recognised unreliable data , why doesn't the system switch off the FD's automatically rather than rely on crew action? Seemed less than helpful.

Last edited by Mr Optimistic; 20th Aug 2012 at 19:36.
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Old 20th Aug 2012, 19:40
  #1447 (permalink)  
 
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jcjeant: so, basically, Mr Christian Roger (who is he?) implies the BEA is lying?
I hope he has solid reasons to do so.
So far, the reasons he gives in your quote aren't enough, and show (IMO) a lack of understanding of the aircraft systems.

1/ the BEA didn't say that 3 ADRs were needed for the Abnormal Attitude Law to be invoked. In fact, it seems when reading IR3/Final report that one ADR would be enough.
It said: "Du fait du rejet des trois ADR par les calculateurs de commande de vol (PRIM), la loi d’attitudes inusuelles n’aurait pu se déclencher que sur des critères liés à des paramètres inertiels, mais de telles conditions n’ont jamais été réunies." // "Due to the rejection of the three ADR by the flight control computers (PRIM), the abnormal attitudes law could only have been triggered for criteria relating to inertial parameters, but these conditions were never met."

2/ AFAIK, the fact that the PRIMs (part of the EFCS=flight controls computers) reject an ADR's data don't imply that this ADR is OFF/FAIL. Proof of that would be:
- that the said ADRs still provided AoA values to the warning computer, which maintained S/W until the ADRs themselves outputed "NCD" values.
- that the IAS was still displayed on the PFDs, even if the ADR were rejected by a flight computer.
You have some insight of this in the §1.6.9.3 of the final report:
"A l’instar des FMGEC, les PRIM valident les paramètres qu’ils utilisent par des mécanismes de surveillance. En ce qui concerne la vitesse air, c’est la valeur votée qui est utilisée. En fonctionnement normal, il s’agit de la valeur médiane. Lorsque l’une des trois vitesses s’écarte trop des deux autres, elle est automatiquement rejetée par les PRIM et la valeur votée devient alors la moyenne des deux valeurs restantes. Mais si l’écart entre ces deux valeurs restantes devient trop grand, les PRIM les rejettent et la loi de pilotage devient alternate 2."
(it's not about the abnormal attitude law, but about the general mechanism of the agreement/rejection of a value by the PRIMs)
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Old 20th Aug 2012, 19:52
  #1448 (permalink)  
 
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The crew had roughly 120 seconds to get into and work themselves out of disaster...

For every second the crew had, thousands of people meeting on a website have had a full week to suss everything from Law to guffaw....

And still no resolution of what the Hell Airbus has in mind for its a/c to give to those flying it.

This is absolutely bizarre.... And here is no stronger way to make this point....

Airbus had/has NO intention of explaining its a/c to those who fly it....

In extremis, complicated is dessicated; get it quick, or die......
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Old 20th Aug 2012, 19:58
  #1449 (permalink)  
 
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Originally Posted by OK465
... but in the current embodiment of Alternate Law, when a THS 'jam' (STAB CTL FAULT) is in effect from either holding the trim wheel or inserting the failure, you will also eventually see triple PRIM PITCH faults.
You raised this issue in a slightly different form a couple of pages back, and the reason I queried you then was that throughout these threads comment has been made about holding the Trim Wheel, and the "devil's doing" now detailed has never been raised. Perhaps this detail, not mentioned in any FCOM, FCTM or Instructor Support Manual I have seen, is the very reason the "never touch the Trim Wheel" myth got a footing.

Is the actual detail to be found in the AMM?
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Old 20th Aug 2012, 20:02
  #1450 (permalink)  
 
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jcjeant: so, basically, Mr Christian Roger (who is he?) implies the BEA is lying?
Christian Roger
Commandant de bord B747 Air France (retraité)
Ex Leader de la patrouille de France
Expert de l'accident de Sharm El Sheik (pour le compte des familles des victimes)
Ancient président du bureau Air France du SNPL (syndicat national des pilotes de ligne 1986-1990)

Captain B747 Air France (retired)
Former Leader of the Patrouille de France
Expert accident Sharm El Sheik (on behalf of the families of victims)
Former president's office SNPL Air France (National Union of Airline Pilots 1986-1990)
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Old 20th Aug 2012, 20:12
  #1451 (permalink)  
 
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Has it at any time been attempted to hold the trim wheel to prevent Autotrim?
Have line pilots ever done this? In addition to quick sticking to prevent the THS from Trimming? Could something have gotten stuck in one of the wheels? Was anyone sitting or resting a foot on the pedestal?

I have given up on trying to understand alternate law. Quantum Physics is intuitive by comparison....
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Old 20th Aug 2012, 20:25
  #1452 (permalink)  
 
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jcjeant: OK thanks

I won't comment here, too much a risk to use inappropriate language.

Check MP
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Old 20th Aug 2012, 21:12
  #1453 (permalink)  
 
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Abnormal alternate discussion is somewhat irrelevant in the context of "no autotrim", since by the time AOA exceeds threshold the THS is already almost maximum nose up.

Had abnormal law engaged and the crew had gotten a clue and pushed, it would only have hindered them in recovery - the THS would not have come back down unless they moved it manually, and the plane probably wouldn't tell them that. Queue another Bournemouth or Perpignan depending on luck - and probably a bunch of people here complaining about why auto trim was turned off in the stall.

If anyone doubts that ADR fail may prevent abnormal law triggering, just look through the reports of sim sessions on these threads, with some saying autotrim stayed in and others that they had to manually trim to recover. The difference is abnormal law, triggered or not depending which ADRs failed when.

@jcjeant

Seems Mr Rogers' Airbus technical experience is unstated...

Without knowing if it is one-AOA, median AOA, all AOA etc. that has to pass 30deg trigger we are looking at well after 2.11:33 and nearer 2.11:45 to be certain. Comparing with the FD trace it's too close to call given the graph resolution, however also need to take into account that there may be monitoring windows to eliminate transients and where we see AOA exceed 30 may be just the start of the window, which may be only 0.5sec (say), but by the end of which the FDRs are off.

Mr Rogers is even more confused than this though, saying both "need for 3 ADR that this law works" and "FD are in operation and therefore at least two ADR". Last I checked, "at least two" is not necessarily "three", and therefore proves nothing.

@Lyman

Has it at any time been attempted to hold the trim wheel to prevent Autotrim?
Have line pilots ever done this? In addition to quick sticking to prevent the THS from Trimming? Could something have gotten stuck in one of the wheels? Was anyone sitting or resting a foot on the pedestal?
yes it has, consequences already noted in other recent posts - fault messages and control law changes that would have shown in FDR.

I have given up on trying to understand alternate law. Quantum Physics is intuitive by comparison....
Only probably (or maybe possibly) intuitive by comparison...
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Old 20th Aug 2012, 22:56
  #1454 (permalink)  
 
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Is the actual detail to be found in the AMM?
That is a very good question.

I have given up on trying to understand alternate law. Quantum Physics is intuitive by comparison....
I got a 'B' in quantum mechanics at UCLA some () years ago. I don't recall a course in 'alternate law' in my program, but maybe the Law School had one.


(Since I didn't really 'master' it, I've still never been able to use anything I supposedly learned about quantum mechanics in my day to day life, other than for occasional teleportation.)
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Old 20th Aug 2012, 23:19
  #1455 (permalink)  
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Thread #10 starts here
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