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AF447 Thread No. 3

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AF447 Thread No. 3

Old 27th May 2011, 13:06
  #21 (permalink)  
 
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Cool

Hi,

In the report chapter "new findings" I read:
The inputs made by the PF were mainly nose-up

I may ask to the pilots in this forum
Is this a normal behavior for recovery from a stall event ?
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Old 27th May 2011, 13:14
  #22 (permalink)  
 
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Hi jcjeant,
Originally Posted by jcjeant
In the report chapter "new findings" I read:
The inputs made by the PF were mainly nose-up

I may ask to the pilots in this forum
Is this a normal behavior for recovery from a stall event ?
No, unless one really want to stay between alpha prot and alpha max with an High AoA protection kicking in Normal Law.
That may be the confusion if one is only trained to low alt, low speed, Normal Law stall recovery, even if both Pilots aknowledged they were in Alternate Law.
Something that need a serious investigation here.
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Old 27th May 2011, 13:19
  #23 (permalink)  
 
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Maybe the reason the PF persists with a nose-up command and then resets throttles to idle is that his instruments tell him he is diving and overspeeding????
Then why give TOGA power? The report clearly says that the pilot reacted to the stall with TOGA power and a pitch up command. That's the puzzling aspect.

Of course it crossed my mind that for some reason he thought he was diving or gaining too much speed. But then he would not add power.
It just makes no sense.

And it is not a momentary confusion either, it is a persistent pitch up command. There were two other pilots there who did not react to this inconsistent action by the PF which makes it all the more puzzling. I maintain that we are missing half the information.
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Old 27th May 2011, 13:22
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Cool

Hi,

In one of the graph (point number 6) the aircraft made a turn to the right (and not a small turn!)
How that can possible as in the rapport the first PF action is a command to climb with a turn command to the left ...
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Old 27th May 2011, 13:24
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What I believe the report doesn't say is what the PF instruments were saying.

In the BEA BAC 111 incident in the 70s the crew had both overspeed and stall warnings at the same time - caused by ice in the pitot and static lines.

There was somewhere over Asia a pitot ice problem just after the AF with prang similar instrument indications to the 111.

I read the post from the crew on PPRuNe.

The skipper stated that if it had been at night they might not have got away with it.

Speaking from my own experience only - If the choice was overspeed or stall then I would lean towards stalling as with a gross overspeed one has no chance to recover.

On early jets - 707 etc - with an overspeed you opened the airbrakes immediately - did it once in wave over the alps after returning from the call of nature and not realizing the ball park had changed.

Assuming there was not a flight control system fault then it seems as though PF didn't understand what was going on.

Which leads to a post I made last week - why don't they fit AOA instruments?

Lost my best friend in a stall which was not identified nearly 40 years ago and eff all appears to have changed.
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Old 27th May 2011, 13:27
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Well, there is an AOA instrument on board: the stall warning
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Old 27th May 2011, 13:29
  #27 (permalink)  
 
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Cool

Hi,

both Pilots aknowledged they were in Alternate Law
In alternate law .. the trim is in "auto-trim" ?
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Old 27th May 2011, 13:34
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@ silverline001 : Les Airbus A330 d’Air France sont équipés du radar Collins WXR700X. L’image radar est présentée sur les ND, superposée aux autres informations.
Source : BEA's interim #1 report, dated july 2009.

@ jcjeant : A roll command to the left is not a turn command to the left. Particularly when this roll command seems aimed to counter an aircraft roll to the right...
Are you already trying to find a reason to disregard the last BEA sayings ?
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Old 27th May 2011, 13:34
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And it is not a momentary confusion either, it is a persistent pitch up command. There were two other pilots there who did not react to this inconsistent action by the PF which makes it all the more puzzling
My emphasis added.

We do not know that the others didn't react, as the report does not tell us either way. The report does note, however, that the PF and PNF both did something a 2:13:28 (1 minute before impact), at which point the PF handed over control to the other. So there does seem to have been some reaction.

Edited to add emphasis.
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Old 27th May 2011, 13:36
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infrequent flyer: this is a wirehead question in two parts, but I'll ask anyway.

1. What parameters inform (other than sidestick command, or in mechanical back up mode the trim wheels) how the THS moves up or down?

Are the inputs into Pri or Sec that lead to THS commands (which include autotrim commands)
-airspeed?
-AoA?
-a blend/sum of both?

(Are other intertial systems inputs summed in to create the final signal? the (dated) block diagram doesn't get into the wire and signal inputs and loops).

2. As I understand the (dated) block diagram, mechanical mode (trim wheels) does not command the elevators, it commands only the THS.
(If I have misunderstood this, please advise).




Interesting comment on the old training aid I am referring to:

Regardless of pilot inputs, the computers will prevent :
- excessive maneuvres
- exceedance of the safe flight envelope

Last edited by Lonewolf_50; 27th May 2011 at 13:48.
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Old 27th May 2011, 13:39
  #31 (permalink)  
 
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Another puzzling combination, in addition to the already mentioned ones,is that with the application of TOGA they gave a pitch Up input, and when they applied IDLE power they gave a pitch Down input...I don't get it, it's the inverse of what you might expect: TOGA application makes sense in a stalled condition together with a pitch down input, and IDLE application makes sense in a overspeeding condition where pitch Up might be required. Something is missing or I'm missing something.
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Old 27th May 2011, 13:40
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Originally Posted by jcjeant View Post
Hi,
How it's possible that the horizontal stabilizer stay in climb position when the PF perform a dive command ?
Don't know yet - very likely will be part of the detailed technical investigation.

Some possibilities (from my basic understanding of the engineering)

a) because auto-trim has been lost, it's not there in all laws (not clear this is what happened in this case)

or

b) because autotrim went wrong - possibly due to invalid speed input to gain

or

c) because maybe the pitch-down input was brief and/or could be satisfied without moving THS

Remember the pilots went hard pitch up (to the "stops"), then briefly pitch-down, quite possibly the attitude never reached level let alone "dive". BEA states that "angle of attack decreased" following the pitch-down - therefore the it appears the a/c was still responding to pitch controls (and in the right direction, but at what rate?). Shortly after, the pilots comment about reaching FL100, and there are further control inputs - not specified, but possibly pitch up again...

Another consideration:

BEA: "The airplane was subject to roll oscillations that sometimes reached 40 degrees."

From http://www.airbusdriver.net/airbus_fltlaws.htm:

No requirement to change pitch trim for changes in airspeed, configuration, or bank up to 33 degrees.

Not clear what those two taken together mean - maybe autotrim stopped temporaily due to the roll angles.


Note: there is still insufficient information to say the aircraft and flight control systems are in the clear, but equally not enough to show they are to blame. We do know, however, that the aircraft didn't pitch-up and stall on its own - pilot inputs were made. I'll leave those to the heavy pilots to discuss.
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Old 27th May 2011, 13:42
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I think there is vital information not presented in the report. In particular the position of the thrust levers is only given at a couple of points. We know PF dialled in a lower speed because of turbulence and shortly afterwards AT disengaged. How long after this point did the PF touch the throttle levers to increase thrust? I don't think we are told. Later, after the first stall warning, the engine levers at at TOGA. It would be very useful to see a graph of engine N1 over the whole period.
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Old 27th May 2011, 13:44
  #34 (permalink)  
 
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Originally Posted by jcjeant
In one of the graph (point number 6) the aircraft made a turn to the right (and not a small turn!)
How that can possible as in the rapport the first PF action is a command to climb with a turn command to the left ...
An explanation was that the right wing stalled, due to lack of speed, and then the PF tried to counter it by rolling to the left, but it is useless or will make the things worse.
Originally Posted by jcjeant
In alternate law .. the trim is in "auto-trim" ?
Until you are using the manual wheel which is overriding it.
Originally Posted by geoff sutherland
Maybe the reason the PF persists with a nose-up command and then resets throttles to idle is that his instruments tell him he is diving and overspeeding?
Recorded (and displayed) speed dropped (LHS and stand-by) due to ice, down to 60 kt (false) during one minute and come back to 215 (real), then 185 (real). They heard those stall warnings... no overspeed.
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Old 27th May 2011, 13:54
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I don't think many have experienced a stall in a turbulent cell before. Recognizing that the aircraft had indeed stalled might have been very difficult at night (as Blind Pew referred to earlier) and with all the alarms going off. (And agreed, the stall warning should have been a primary indication but that was preceeded by other alarms.) Once established in the stalled state, the aircraft still had roll control and may have been fairly stable in that state with no further stall breaks, causing confusion as to the correct action to perform. Nowhere in that report do I see any overspeed reference so why forward stick was not applied is very odd unless the effects of vertigo were so convincing. THS up trim to 13 degrees up (whether done by the system or manually) definitely needs to be analyzed and understood.
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Old 27th May 2011, 13:54
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Originally Posted by Lonewolf_50 View Post
infrequent flyer: this is a wirehead question in two parts, but I'll ask anyway.

1. What parameters inform (other than sidestick command, or in mechanical back up mode the trim wheels) how the THS moves up or down?
Afraid you are crediting me with more detailed knowledge than I actually have.

Short answer - I don't know, but it is one of the questions on my mind too...
I strongly suspect that airspeed is in there somewhere, but what value is used when airspeed is known-invalid, I have no idea.

Regardless of pilot inputs, the computers will prevent :
- excessive maneuvres
- exceedance of the safe flight envelope


And the concierge can fly it too...

All missing the big caveat "as long as everything works normally" (and actually, even then the concierge quote is rubbish). Drop out of normal law and all that no longer applies.
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Old 27th May 2011, 14:00
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Maybe the reason the PF persists with a nose-up command and then resets throttles to idle is that his instruments tell him he is diving and overspeeding????
There's a stall warning at 2:10:51, then the report notes that the stall warning horn stopped at 2:11:40, the clear implication being that the horn was sounding throughout the intervening period. So the instruments could not have been telling the PF he is overspeeding, as the instruments clearly thought he was stalling -- and saying so.

So it seems more likely he did not believe the instruments. Or is it possibile he misinterpreted the protections the current law was providing? If he thought he still had stall protection, would commanding pitch up be a way of trying to tell the aircraft: I don't want to lose altitude, and I'm relying on you not to let me stall?
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Old 27th May 2011, 14:03
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[email protected], what you described looks like a hybrid between a spin and a spiral.
Once established in the stalled state, the aircraft still had roll control and may have been fairly stable in that state with no further stall breaks, causing confusion as to the correct action to perform.
Spin in the goo, in a CB? Ouch. (EDIT: Capn Bloogs, thanks, not in a cb, but in the goo nonetheless)
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Old 27th May 2011, 14:03
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What parameters inform (other than sidestick command, or in mechanical back up mode the trim wheels) how the THS moves up or down?
Load factor. This is only a load factor law supposed to maintain 1g flight by small adjustement of the horizontal stab trim (and it is only commanded by the PRIMs).

Last edited by takata; 27th May 2011 at 15:08.
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Old 27th May 2011, 14:04
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Press can't read English or French...

The rubbish has started in the "press" - front of dailymail website (my bold):

Passengers and crew on board doomed Air France jet endured terrifying THREE MINUTE plunge into the ocean after engines failed
The pilot, Marc Dubois, had been taking a break when the plane hit heavy turbulence and never returned to his seat before the crash.
So, no one (as there's only one pilot, singular) at the controls, heavy turbulence, engine failure.
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