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AF 447 Thread No. 7

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AF 447 Thread No. 7

Old 1st Dec 2011, 08:20
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I translate the original as follows:-

"The position of the rudder limiter of the rudder (RTLU) is frozen at 2 h 10 min 04.5 and the unavailability of the rudder travel limiting function is recorded between 2 h 10 min 17.5 and 2 h 10 min 18.5."

Do you believe that the wording used in the French version effectively means that, "The RTLU is locked at the allowable deflection for the last valid Mach speed"? If so, that statement matches the operational description of the device.

In respect of the earlier variations; would seem that there were some short-term Mach fluctuations prior to the defining one.

Last edited by mm43; 1st Dec 2011 at 19:59. Reason: spelling
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Old 1st Dec 2011, 08:53
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Hi mm43;

Thanks for sharing my curiosity. I think your translation is perfect and, yes, I believe it means what you say (i.e. the 'freeze & latch' corresponds to the CAS & Mach at 02:10:04,5). The "short-term Mach fluctuations prior to the defining one" must have been pretty large, and must have come from a different source than the recorded CAS & Mach. Then there is the value itself, which doesn't correspond with IR #2:
1.12.3.5.5 Examination of the Rudder Travel Limiter Unit (RTLU)
The RTLU was found in its place in the fin and disassembled. An examination was performed at the manufacturer’s and showed that it would allow travel of the rudder measured as 7.9° +/- 0.1°. As an example, at FL350, this travel is obtained for Mach 0.8 +/- 0.004, corresponding to a CAS of 272 +/- 2 kt.
Note: the maximum travel of the rudder is calculated in relation to the airplane configuration, its speed and its Mach number. This travel can be commanded between 4 degrees and 35 degrees.

Last edited by HazelNuts39; 1st Dec 2011 at 09:11.
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Old 2nd Dec 2011, 07:38
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Hi HN39;

Thanks for the reply. I will answer the PM in due course.

Looking at the Yaw Damper trace, I believe that the maximum rudder angle allowed by the Yaw Damper (+/-4°) was not exceeded, but whether the damper was acting correctly is another matter.

The DA displayed by the TLU is rather puzzling. Perhaps the TLU angle doesn't represent the actual rudder angle, but there doesn't seem to be a valid reason for that to happen. As the AMM doesn't shed any light on the situation, we may just have to wait for the BEA to explain exactly what was happening.

As you have already pointed out, if the deviations shown in the TLU traces are to believed, where did this Mach data come from?

Having searched the various definitive sources and found nothing, I reverted to the Cathay Pacific notes originally compiled by Andy Tracey and came up with this for Yaw and another for ALT-2.

EDIT : Basic control schematic

Last edited by mm43; 2nd Dec 2011 at 16:53.
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Old 3rd Dec 2011, 16:50
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@Lyman
"His Pull was additive to an input made by AutoPilot"

Forget !
Impossible . You know : BZ said : pilots are only housekeepers, cow-boys or fools ! It would be a real algorithm bug in AB philosophy to add a computer and a human input !
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Old 3rd Dec 2011, 18:15
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BZ , himself , a cow boy , cutting telepheric lines in Alps with a Mirage 3 .

Short memory Bernie !
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Old 3rd Dec 2011, 18:44
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For the uninitiated, is that post supposed to mean anything in particular?
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Old 3rd Dec 2011, 20:02
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For the uninitiated, is that post supposed to mean anything in particular?
In the 60's Bernard Ziegler's F84 collided with the line of a cable car in the Alps, killing 6 people. It's routinely dragged out to serve as proof that anything Airbus is inherently evil. Link
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Old 3rd Dec 2011, 20:28
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@Zorin:
Ah! The light dawns. Thanks!
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Old 3rd Dec 2011, 22:05
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Bon Temps Rouler....

ne plus plus. At handoff, the airframe was rotating up, as the ascent diminished, (The PITCH on PFD showed 0, four degrees 'low'). My surmise is that the PF's initial NU input created an unwanted PITCH moment (Normal Law, protected), and that caused the STALLSTALL, (the first WRN, a 'transient'). Still sufficient for the highest g accel, though.
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Old 5th Dec 2011, 14:36
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Lyman, for what it's worth ...

IF you are a pilot flying on instruments,
AND
you (or your friend HAL) make a pitch input that causes the nose to go up ...
AND IF the nose goes higher than you intended it to to go when you or HAL made that input
THEN
you use your hand on the flight controls to make an immediate counter correction that is usually accomplished in two parts (particularly if your task is to fly smoothly in order to keep your passengers as comfortable as you can)

a) first you stop the pitch rate (and you watch all of this on your attitude indicator/AH) and
b) make a second correction to return the nose to the pitch you actually desire for the flight conditions or performance you wish to complete your mission, or the segment of the mission you are on.

As an adjunct:
IF during this process you find your aircraft to be rolling beyond the AOB you desire (which I think would be "wings level" or "0" degrees AOB)
THEN you use that same hand to stop roll, and work the wings back to level via small corrections, or one larger correction. Given what A330 experienced pilots who have posted here have shared, at that altitude the small corrections might be the better technique, as they adivse us that the A330 is sensitive to input in that flight regime when hand flying.

ASIDE: Any pilot who cannot correct for pitch and roll at the same time by referencing his attitude indicator cannot be considered to be qualified to pilot a passenger jet. I am sure both of the pilots in that cockpit had demonstrated time and again that they could make such an input in two axes successfully. I seriously doubt AF would have hired them had they not been able to. The answer to why neither did in this instance, particularly the pilot who handled the controls at the handoff from HAL to Human, remains incompletely answered to my eye, other than to consider comfort with the aforementioned sensitivity to input. What did he see?)

So, even if the plane at hand off was in a non stable state -- which is part of your point -- a change in nose pitch, or a continuation of a nose pitch change in one direction or another is not necessarily a fait accompli if the pilot whose hand is on the stick flies in accordance with standard instrument flying principles, principles he had previously shown he could apply consistently. (For this and other reasons the "pitch and power" chorus has been singing in three part harmony on these forums since about 01 June 2009 .)

Your analysis of what the pitch result was, in and around that point in time, must to be complete (IMO) include a consideration of what flying performance was desired at the time.

At the altitudes in this event, 11 degrees nose up borders on an unusual attitude, for the flight condition and peformance desired on that leg of the mission: straight and level.

Last edited by Lonewolf_50; 5th Dec 2011 at 14:50.
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Old 5th Dec 2011, 16:11
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"The aircraft did not immediately respond..." BEA

This plays Hell with your primer, Lonewolf. Notwithstanding the Pitch was four plus degrees low on the pilot's AI. The STALL WRN suggests an AoA of extreme value, v/v cruise, and the a/c was maneuvering out of phase with its attitude, eg, Nose Low, and ascending.

At the very least, we suspect the airframe was not consistent with a ho hum cruise, and the a/p (imo) quit due controls/response out of limits. To include airspeeds discrepant: either disagree or simultaneous migration past a/p limit value. (30 knots < second and continuous). See the Mach variations as described above.

The only aspect consistent with a STALL Warning, at that speed, is AoA/Mach disagree, which is consistent with the accepted wisdom, here, as I see it, but not enough acceptance/credence is lent to the conditions extant at a/p loss/handoff/HAL malfunction.

It is troubling that without the conditions leading up to handoff, so many here have arrived at conclusions. You suggest a lack of skill is responsible.
The DFDR is reporting Inertial data, not what PF or even you would be seeing at the beginning (or 'continuation' of UPSET).

It is vital that the conclusion be exculpatory of the Bus. If due Weather, then the a/p v/v limits in stink is suspect. If a/p exceeded, the Bus is painted as poorly designed. How handy for a baby pilot to put them into the wet.

My starting point is that the crew inherited an upset airframe. The autopilot's limits are well past what is technically accepted as "Upset" in the regs. So naturally, ICE and inexperience are the uniform of the day.

The story is here, in the start, not at the (actual) STALL.
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Old 5th Dec 2011, 19:02
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What blows my mind is your willingness to set aside the fact of (at least) 37 previous incidents of ice-caused UAS using a known-to-be-defective pitot. Instead you become an intellectual contortionist, sir.

There are plenty of confusing factors to this accident without all this stuff you're coming up with.
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Old 5th Dec 2011, 19:38
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Lyman, taking a plane that is not stable, if HAL did something odd, is roughly the same as taking the plane from another pilot who is flying badly or has vertigo. If you fly in multi-crew aircraft, I run with the assumption that the above is one of the tasks that you are required to do, and trained for.

If you are not trained to do that, one wonders "Why not?"

I refer you again to my old refrain: what did he(PF) see? Though the betting money is on all of the AH's working, the PNF did switch sources to a different inertial gyro for one reason or another.

What was that reason?

More than one possible answer, and since they didn't verbalize why that was done, the why is left open to some question. Those who have flown the A330 may be able to offer better estimates that I, so I won't attempt to.

Nothing further.

Out.
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Old 5th Dec 2011, 21:27
  #574 (permalink)  
 
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Originally Posted by Lonewolf _50
... what did he(PF) see? Though the betting money is on all of the AH's working, the PNF did switch sources to a different inertial gyro for one reason or another.
The PNF was apparently looking at all three displays between 02:10:25 and 02:10:36:
Reading the three instruments (the two PFD’s and the ISIS), the PNF noticed that the
airplane was climbing and asked the PF several times to descend.
Subsequently he made following selections:
02:10:40 F/O on ADR3
02:10:44 F/O on IR3
02:12:15 CAPT on ADR3
02:12:19 CAPT on IR3
02:13:25 CAPT on ADR1
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Old 6th Dec 2011, 00:55
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Originally Posted by HN39
The PNF was apparently looking at all three displays between 02:10:25 and 02:10:36:
Reading the three instruments (the two PFD’s and the ISIS), the PNF noticed that the airplane was climbing and asked the PF several times to descend.
Subsequently he made following selections:
02:10:40 F/O on ADR3
02:10:44 F/O on IR3
02:12:15 CAPT on ADR3
02:12:19 CAPT on IR3
02:13:25 CAPT on ADR1
Logically, PNF wanted to be sure that PF was flying with information that looked good to PNF and so that he, PNF, could be sure of what was appearing on PF's panel. (Since monitoring the PF's PFD was a bit of a stretch for PNF.)

Obviously PNF trusted the ADR3/IR3 data and likely didn't understand why PF insisted on flying around with his nose in the air.

Then later, to ensure that he could also conveniently read the ADR3/IR3 data on his PFD, he switched his displays to the same data sources. (Despite the loss of redundancy.)

That is my take on these actions. Sorry about all the acronym soup.
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Old 6th Dec 2011, 07:30
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It seems to me he primarily switched the Air Data source, just taking the Inertial Reference along without any particular reason.
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Old 7th Dec 2011, 14:39
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Thank you both for your thoughtful estimates.
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Old 8th Dec 2011, 03:38
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Popular Mechanics: What Really Happened Aboard AF447

Popular Mechanics has a new article on its Web site today discussing "What Really Happened Aboard AF447." The article includes the final conversations of the crew, along with analysis. According to the PM version, the captain does finally realize the plane is in a stall, and in the last seconds tries to point the nose down, but they run out of time.

Print - What Really Happened Aboard Air France 447 - Popular Mechanics
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Old 8th Dec 2011, 11:22
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Originally Posted by PM article linked in the post above
An even fuller picture emerged with the publication of a book in French entitled Erreurs de Pilotage (volume 5), by pilot and aviation writer Jean-Pierre Otelli, which includes the full transcript of the pilots' conversation.
I disagree. Having read the book, I commented it here.

The "picture" in Otelli's book indeed adds some points to the data contained in the BEA's last interim report, but on the other hand it lacks of data/information on some other points.
=> Describing it as "fuller" is in my opinion a bit of an overstretch, and carries implicitely the impression that some things are "hidden" by "the authorities" (BEA), which constitute a polemic, not a fact.

---------

The quoted article lacks some nuances (which can be of importance, when really wanting to understand). Let's try to correct some of that:

02:06:50 (Bonin) Va pour les anti-ice. C'est toujours ça de pris.
Let's go for the anti-icing system. It's better than nothing.
"It's better than nothing." feels pessimist. The exact translation for that exists and is used in french: "C'est mieux que rien". That's not what the pilot said.
"C'est toujours ça de pris." is optimistic. They turned on the anti-ice, as a precaution against potential icing conditions. They didn't turn on the anti-ice as a mean to try to limit an already bad known problem.


02:08:07 (Robert) Tu peux éventuellement prendre un peu à gauche. On est d'accord qu'on est en manuel, hein?
You can eventually pull it a little to the left. We're agreed that we're in manual, yeah?
In french, "éventuellement" means eventually in the sense of "possibly". Not in the sens of "in the end".


02:10:31 (Robert) Tu redescends... On est en train de monter selon lui… Selon lui, tu montes, donc tu redescends.
Descend... It says we're going up... It says we're going up, so descend.
The BEA report differs :
2 h 10 min 33: (PNF) Selon les trois tu montes donc tu redescends
=> According to the three you’re going up so go back down
"Les trois" (the three) is important, it means the PNF refers to 3 indications (either the 3 ADIs, or the ADI and the V/S and the altimeter)


...

I leave it there, just wanting to try and convince you:
1/ to read the article (it's interesting in quoting extensively Otelli's book, only published in french AFAIK)
2/ but to exercice caution. The advertised "full transcription" (and implicitely "full explanation") is marketing to sell paper...

Cheers
AZR
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Old 8th Dec 2011, 17:22
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At the crucial moment of a/p loss, the airframe was climbing, and the Nose was Pitched down. Added to that, the bank angle was about 8 degrees Right wing low (turbulence?). The a/c had it right, they were in a robust upwelling, an updraft, and the Nose was commanded down, though the a/c still climbed. We do not know for how long the a/p had been maneuvering in this fashion, though it can be said that the pilots themselves, in discussing temps and calling the back for a HU on turb tells us it was not new.

It is this possibility that has been actively ignored. I believe the PF made a correction in Pitch that was perhaps the opposite of what was needed. Climbing in the airmass, a NU creates more climb, in g and in VSI.

Much is made of their presence in a cell, though the possibility of a robust UD is dismissed?

The column may have been 120 knots. If so, this plays havoc with airspeeds, AoA vanes, and 'feel'. The airspeed in descent could have been twice that reported by the DFDR. "I think we have crazy speed..."

As with any epic disaster, those whose fingerprints are on the investigation call the shots. Though BEA have not done so, the focus is on the 95% of what is utterly irrelevant to the disaster.

What caused the climb to Stall is virtually ignored, and when addressed, data is ignored, and the audience is expected to sign on.....

I think PF did fly attitude, more's the pity. And Power was not a player, not at first.
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