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AF447 Thread No. 3

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AF447 Thread No. 3

Old 28th May 2011, 21:34
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ask26


Could that desire not to lose altitude be linked due to the weather deviation,(which I think could be one of the psychological factors affecting the PF's initial reaction) in that they were just clearing the tops of a cell and were worried about the subsequent impact of losing it. Hence the application of TOGA to attempt to compensate for the pitch up.
You know, you may be so on the money.

All the "haters" on here can't even recognise a simple human decision, a decision made in an attempt to avoid further "difficulties".
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Old 28th May 2011, 21:35
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clandestino:

To set the record straight: horizontal stabilizer is very effective and it has no fixed part whatsoever.
You are right. It is trimmable and it was 13 degrees down (pitching-up). With 107 kts ground speed it could maintain a 16 degrees a/c pitch-up attitude.

Let's get back to automation, then...

P.S.:

Somebody must have asked this before:

If the trim was not performed by the PF but by HAL would the PF be easily aware of this ?
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Old 28th May 2011, 21:38
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Originally Posted by mitrosft
- Hey HAL your air speed dropped from 275knots to 60 knots WITHOUT any decceleration!

-So disregard your speed change and keep the current flying parameters - thrust and pitch. Until deceleration/acceleration tells it that speed changed.

And then give pilots info about unrelaible airspeed.
Which is what it does, and what happened. With the addition that because speed is known-bad the speed-based protections drop out. And control gets handed to the pilots - because HAL isn't sure what the plane is doing any more.

With no control inputs, the plane should just keep doing what it was doing before, here something causes a roll and pilot responds with full back stick and all hell breaks loose.
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Old 28th May 2011, 21:41
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I have to wonder if the initial thought of the PF was (after auto pilot, A/T disengage) to not let the aircraft increase its speed due to the anticipated turbulence upcoming. Remember there was a crew communication to the cabin about "it'll move about a bit more than at the moment" (2h06m04), along with the crew deciding to reduce speed from .82 to .80 a few minutes later (2h08m07) due to the anticipation of turbulence - "turbulence increases slightly". About 2 minutes later is when the A/P and A/T disconnect and the speed drops from 275kt to 60kt and a few seconds later the crew identified "so, we've lost the speeds". So now recognizing that they had invalid speeds, and knowing they needed to avoid penetrating the turbulence at too high of a speed, I wonder if the initial thought was to apply nose up inputs to ensure turbulence penetration speed was not exceeded. I also have to wonder with this being fresh on their mind, it might have been their initial concern when losing the speed indications, that we can't penetrate the weather at too fast a speed. Then while troubleshooting and dealing with everything going on and possibly being distracted, realized there was too much nose up input and went to nose down (7000ft/min to 700ft/min) You also have to wonder if through this whole ordeal, if that was something they were fighting if they were in IMC conditions and rough air for most of the 3 1/2 minutes.

Right or wrong, I just know that the weather and reducing speed was fresh on their mind. When the A/P and A/T disengaged, maybe there was zero panic and they were confident how to handle the situation and simply were going to wait for the speeds to come back. The other thing that caught my attention...was the crew briefing just before the captain left. The briefing from crew, was that they couldn't climb right now "we’re in the cloud layer unfortunately we can’t climb much
for the moment because the temperature is falling more slowly than forecast" - So I have to wonder if that is something they had discussed earlier about possibly trying to climb above the current cloud layer, but couldn't due to conditions and aircraft config at the time. When they lost the speeds, I wonder if there was a thought of trying to climb if they could to see if they could get to 1)smoother air and 2)out of the cloud layer to hopefully clear the pitot sensors.

I am probably reading between the lines, and CVR recordings would help to identify some of this. I just find it interesting that climbing was part of the crew briefing.

So did the PF try to pitch up slightly to keep the aircraft speed below .80 since they were now more than likely penetrating turbulent air? And was there a desire to see if they could get to a higher altitude (out of IMC) to help resolve the issue with the speed sensors? Again right or wrong from SOP, but it could point to one of the reasons of nose up initially. Once they entered a stall, that created a whole host of other challenges.

I haven't flown in a few years and only flew corporate jets for several years, but the mindset of the pilots will be very hard to decipher even with CVR recordings, which will help to paint a better picture of what they were thinking. I want to be able to give the pilots the benefit of the doubt and would like to think that there was some logic in the initial nose up and at other times nose up commands. As pilots, we need to be supportive of each other, and realize that many of us have been fortunate enough to not have to deal with a "hairy" cockpit in our careers. But for those that have, like this crew, we have no idea what was going through their heads.
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Old 28th May 2011, 21:42
  #465 (permalink)  
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So who has eliminated all but UAS? What was PF's initial control input, a rather robust response and result. What caused his reaction? Did a/p drop before or after, and either way, was its involuntary loss linked to the manouver? The conditions in the cell? Fixation is neurotic........and leads to accusations and unsupportable claims. Just for review, a Stall warning is not necessarily a Stall.
 
Old 28th May 2011, 21:42
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Having spent years watching crews in the sim sorting out problems and noting the time it has taken them, three and a half minutes is not a lot.
It depends on how you look at it. Four minutes is a lot of time for two pilots to be startled or surprised. It's not a lot of time for pilots who are confused. I think it's important to be quite clear and specific in regard to the terminology used.

In any event, I think the time issue is a red herring. What the flight crew should be judged upon is not the length of time they had but how they utilized the time they did have. Was their behavior in accordance with their training? Was it up to professional standards? The fact that there was only four minutes before the plane crashed was not a predetermined parameter set in some sim session; those four minutes were a function of the flight crew's inability to prevent and then recover from a stall.
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Old 28th May 2011, 21:46
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Originally Posted by Teddy Robinson
Nobody has mentioned "deep stall" in any published information so far released.
That depends on how you define "deep stall". From BEA's Update Findings:
- the descent lasted 3 min 30, during which the airplane remained stalled. The angle of attack increased and remained above 35 degrees, (...).
The last recorded values were a pitch attitude of 16.2 degrees nose-up, a roll angle of 5.3 degrees left and a vertical speed of -10,912 ft/min.
For a groundspeed of 107 kt, the last recorded values (assuming no wind) correspond to a flight path angle of 45 degrees down, i.e. an AoA of 61.2 degrees. Deep?

Last edited by HazelNuts39; 29th May 2011 at 13:26. Reason: wind assumption
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Old 28th May 2011, 21:54
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mm43, nose never down notwithstanding the PF pushed the stick forward.

At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law […]".

The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs. The vertical speed, which had reached 7,000 ft/min, dropped to 700 ft/min and the roll varied between 12 degrees right and 10 degrees left. The speed displayed on the left side increased
sharply to 215 kt (Mach 0.68). The airplane was then at an altitude of about 37,500 ft and the recorded angle of attack was around 4 degrees.
The plane was stable for about 35 seconds before another stall warning, which may be appropriate given speed and altitude. What happened next seems to make no sense. I also wonder why PF did not push stick forward again to initiate a descent back to FL370, which would be safe and beneficial given the speed report that returned. Of course, he may not have trusted it.
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Old 28th May 2011, 22:03
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At 2 h 08 min 07 , the PNF said "you can maybe go a little to the left […]". The airplane began a slight turn to the left, the change in relation to the initial route being about 12 degrees. The level of turbulence increased slightly and the crew decided to reduce the speed to about Mach 0.8.
Nothing there to pull the nose up.

From 2 h 10 min 05, the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input.
The nose-up input - would that be to maintain altitude while correcting the roll? It does not say how large a nose-up input was made for how long.

At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law […]".

...

The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs.
If the PF had not made a very assertive nose up what brought the nose up 6 whole degrees on a plane with that mass? (Mind you, I am not at all sure an updraft would lift the nose.)

(And I keep quoting because it seems some of us are not working off the same document. That way the source of my confusion is at least well delineated. I'm not trying to be a smartass - except maybe to bienville. He twisted my tail.)
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Old 28th May 2011, 22:06
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Stall warning => nose down or die

"A formal document detailing the rationale for the revision points out: "There have been numerous situations where flight crews did not prioritise [nose-down pitch control] and instead prioritised power and maintaining altitude."
Operational experience has shown that fixating on altitude, rather than the crucial angle of attack, can result in an aircraft stalling."
Revised stall procedures centre on angle-of-attack not power


A pilot that doesn't nose down immediately when earing a stall warning has not understood what is a stall : the plane is no longer a plane, it is a cucumber.

When you ear a stall warning, you are about to die within a min => you don't even remember your name : you nose down.

The trouble is that :

" The statistical data shows that, when confronted by a stall, in 80% of cases, pilots pull back the control column, in a sort of reflex movement, which continues the loss of control.
The aircraft was subjected to a series of four full and rapid rolls. The first was attributed to the force brought to bear by the pilot on the left part of the control column; the following ones were due to pilot overcompensation on the roll then the stall. Having pulled the control column fully back and thus caused maximum nose up pitch, the pilot rectified this by pushing the control column fully forward. The aircraft dipped, with its nose going under the horizon by 32°. The roll-off from +50 to –32° in seven seconds was remarkable."

REPORT on the incident on 24 September 1994 during approach to Orly (94) to the Airb
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Old 28th May 2011, 22:07
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Deep stall post referenced

Hazel, et al.

I re-posted the deep stall stuff an hour ago.
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Old 28th May 2011, 22:13
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CogSim, good catch on the PF never acknowledging the PNF statements. It certainly does seem to match a hypothesis that PF was fixated on the unitial WTF moment.

Clandestino, the initial nose down command was way before the THS was stuck at 13 degrees. That started about 35 seconds later in the sequence at 2:10:51. And as I read it 2:10:51 was the start of THS movement from 3 degrees to 13 degrees.

{^_^}
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Old 28th May 2011, 22:23
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"Transfixed like a possum caught in the headlights"

that, quite possibly, could be the conclusion drawn based on what has been released so far, still, until the investigation process has properly run it's course, and the full transcript released set in context, on a time line, it is all too easy to draw conclusions, when there are levels of other systemic failures that are not so easily identified.

I would expect the rate of BEA press releases to slow down from this point until the release of an interim report.

Re: deep stall, at this point, unless the term is specifically used by BEA, it remains conjecture. High A of A, high descent rate, low forward speed may fit the base line criteria for a deep stall condition, however, the term used is a recognised condition, which until officially cited by the investigation as affecting the airframe, on a type and configuration not usually affected by the phenomenon, may be a reasonable descriptive term in conversational terms ... but ...

Sorry for being pedantic.

Last edited by Teddy Robinson; 28th May 2011 at 22:36. Reason: update
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Old 28th May 2011, 22:24
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Clipped from an earlier post..

From 2:10:05 — The autopilot and auto-thrust disengaged and the PF said, "I have the controls." The airplane began to roll to the right and the PF tried to raise the nose up and to the left. The stall warning sounded twice in a row. Recorded parameters show a sharp fall in speed.

2:10:16 — The PNF said "so, we've lost the speeds" then "alternate law
Thats less than 11 seconds from tripping the autopilot to a stall warning. I'm not a jet pilot but that sounds quite fast. Is it?
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Old 28th May 2011, 22:27
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JD-EE

From 2 h 10 min 05, the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input.

02:10:05...The airplane began to roll to the right and the PF made a (ONE) left nose-up input.

Mademoiselle, M'aider, sil vous plait? Qu est-ce que c'est? La meme chose temps?

The pilot corrects for what the a/p had trimmed out, a right roll and down Pitch.

At a subsequent time, they note the speeds are belly, and the climb commences. These events are linked, yes? I note also the similar input at the top of the climb. Do we know this aberrant non-cruise event is ICE related?

I appreciate your collating the chronologue, it is very helpful. Has anyone posted the possible encoutered verticals in a cell?
 
Old 28th May 2011, 22:32
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Elevator control.

Svarin post #237 http://www.pprune.org/tech-log/45283...ml#post6477847

Three out of five components of the Flight Controls System have suffered anomalies :

- PRIM2 suffered a connectivity problem with ADR1, such problem is deemed HARD, which means permanent, not transient.
- PRIM1 stopped operating.
- SEC1 stopped operating.

These anomalies have consequences which can be verified using the Flight Controls Reconfiguration Schematics from FCOM chapter 27 :

- PRIM2 is tasked with THS motor because PRIM1 quit.
- PRIM2 is tasked with both elevator halves because both PRIM1 & SEC1 quit.

Additionally, PRIM2 operation is polluted because it lost connectivity with ADR1, thus reducing its discriminating capability while simultaneously getting fed multiple erroneous ADR data.

This simultaneous double failure condition : connectivity + erroneous data, is an extremely serious issue. I very much doubt that such apparently unrelated, simultaneous, totally different failures (external cause -> icing + internal cause -> wiring) were ever considered together during the design phase of the Flight Control System.

This extraordinary combination precisely affected the one computer which ended up being tasked with :
- interpreting sidestick commands on the pitch axis.
- sending orders to the hydraulic servo jacks located on the elevator moving parts.
- sending orders to the electric THS motor.
- providing whatever "protection" it deemed necessary to provide while in its undefined state (unreliable ADR data + lost connectivity with one ADR)
In the bold is exactly what in a normal situation PRIM 1 is capable to perform, so shouldn't be a problem for PRIM 2 too.

What I can add to your intresting observation is that in this situation, due to loss of the FCPC1(PRIM1) and FCSC1(SEC1), the Inboard (Green) servos are totally lost (both servos in dampening mode) and therefore are unable to assist the outer servos(BLUE/YELLOW) in large elevator deflections.

From the Technical Training Manual:

PITCH D/O (ELEVATOR) (3)

ELEVATORS NORMAL OPERATION


Each elevator servocontrol is connected to two computers (one FCPC
and one FCSC).
In the normal configuration, the inboard servocontrol is in active mode
while the outboard is in damping mode.
FCPC 1 having the servo-loop control priority:
- sets its dedicated servocontrol in active mode and ensures the servoloop control,
- commands the damping mode on the adjacent servocontrol (one solenoid valve (S) energized).
For the elevator servolooping computation the computers need to acquire:
- the elevator surface position,
- the elevator servocontrol piston position.
This information is sent by servocontrol transducers (XDCRs) units and
the surface position transducer (RVDT).
In the event of large deflection demands, the two servo-controls can
become active to avoid the saturation of one servocontrol.


ELEVATORS ABNORMAL OPERATIONS


HYDRAULIC OR ELECTRICAL FAILURE
If a servocontrol being in active mode is either not hydraulically powered
or not electrically controlled anymore,
the faulty servocontrol falls in damping mode and the adjacent one
becomes active according the servoloop reconfiguration.
If both servocontrols of one elevator are depressurized, both servocontrols are in damping mode which prevents fluttering.
When P1, P2, S1 and S2 are no longer able to control their dedicated
servocontrol (ie: inputs missing, electrical failure, etc...), the servocontrols fall in re-centering mode
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Old 28th May 2011, 22:34
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Originally Posted by ask26 #448
Many people are wondering if as is speculated why the PF pulled up as one of his initial actions. I think on Page 1 of this particular thread one explanation has already been given:
"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?"
Could that desire not to lose altitude be linked due to the weather deviation, (which I think could be one of the psychological factors affecting the PF's initial reaction) in that they were just clearing the tops of a cell and were worried about the subsequent impact of losing it. Hence the application of TOGA to attempt to compensate for the pitch up.
Originally Posted by CoqSim
The sad thing is PNF seemed to be more aware of what was going on. Very early on in the sequence PNF effectively declares, we are in UAS regime and we've lost protections. PF never acknowledges.
These inputs made me think of the Recovery Technique in windshear/downburst conditions (close to the ground), where the pilot is (rightly) encouraged to rely on the High-AoA protections in Normal Law (FCOM 3.04.91, but my copy may not be up-to-date:
- Thrust levers: TOGA; - Follow SRS orders (including use of full back stick if demanded) - Note: If SRS is not available, initially use pitch attitude up to 12.5° but this pitch attitude can be increased by using full back stick if necessary to minimize loss of height.
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Old 28th May 2011, 22:37
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bearfoil:

From 2 h 10 min 05, the autopilot then auto-thrust disengaged
Apologies for butting in, but under what cicumstances or failure modes do these disengage, assuming not the action of the crew ?.

Trying to think logically: This is the first event in the chain. If we know the conditions under which the two disengage, perhaps we can work back from there ?...
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Old 28th May 2011, 22:37
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the initial nose down command was way before the THS was stuck at 13 degrees. That started about 35 seconds later in the sequence at 2:10:51. And as I read it 2:10:51 was the start of THS movement from 3 degrees to 13 degrees.
1. that what you're referring to, sir, is in no way officially connected with BEA and it might be realistic representation of DFDR data or it might not.

2. if, and it's a big if, it's correct and accurate, trim started moving at 2:10:50 and stopped at 2:11:51. Apart from comments about giving mostly climb commands, it can't be seen what was the sidestick displacement or what sidestick was active at all during the period.

3. while we wait for DFDR traces, I'd like to once more remind fellow PPRuNers about AC Doyle's warning on theorizing without facts, the one I've quoted a couple of posts ago.
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Old 28th May 2011, 22:42
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Quite

while we wait for DFDR traces, I'd like to once more remind fellow PPRuNers about AC Doyle's warning on theorizing without facts, the one I've quoted a couple of posts ago.
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