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AF447 Thread No. 3

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AF447 Thread No. 3

Old 27th May 2011, 20:42
  #181 (permalink)  
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The level of arcane systems knowledge this crew needed to dig up in the heat of battle in order to solve the riddle it was faced with is frightening. Having the return of the stall warning triggered by an appropriate control input would have been fiendishly difficult to comprehend under the circumstances. So sad that at this late date new knowledge of our craft is still being written in blood.
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Old 27th May 2011, 20:46
  #182 (permalink)  
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There has been much discussion about what was released today. What is more important, IMHO, is what has NOT been released today. Specifically, the full record of the CVR. There is no question in my mind that there is a whole bunch of communications between the PF, PNF and Capt (when he got back to the flight deck) during that 4 minutes of total confusion.

When I read this report today (and as I reread it again), I did not think for a moment that it includes anywhere near the total cockpit dialog.
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Old 27th May 2011, 20:47
  #183 (permalink)  
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More fascinating than ever. There have been some guesses here that are now proven to be very close to what actually happened.

Without attempting or wishing to accuse/blame the pilots - I wonder if what we have here is a tragic misinterpretation of events?

The Captain returned to the cockpit, but did not feel it vital to assume control - this surely suggests that as far as they believed, the situation was under control.?

Could the pitch up commands have SIMPLY been in response to a belief that the descent was due to being nose down - as others have said - to pitch up BELIEVING that the aircraft is stalled is surely the last thing that you would wish to do - conversely if you believe airspeed is OK then you would naturally 'pull up' to arrest descent.

This theory does not take account of what, if any indications the pilots were (or not) receiving - they either beieved the stall warnings (when they came) or did not. It is hard to believe that any pilot would make a control input (even if it is wrong) UNLESS they believed it was the correct course of action.

So the nub is: simple mistake?
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Old 27th May 2011, 20:48
  #184 (permalink)  
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Speculation of little value.

Originally Posted by grizzled View Post
Mr. Optimistic...

Originally Posted by Mr Optimistic View Post
Is there some dialogue we are missing ?
The answer is yes. Lots. Without any doubt.
Dialog and data missing in copious amounts.

Owing to the lack of meaningful disclosure by the BEA, speculation is fairly useless at this time.
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Old 27th May 2011, 20:53
  #185 (permalink)  
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(3) Why did PF allow/encourage/command A/C to climb 3000ft and up to +16 pitch after receipt of stall warnings? One of the pilots had selected TOGA thrust, presumably in response to them.
Interflug A310 Incident approaching Moscow in 1991 comes to mind.

ASN Aircraft accident Airbus A310-304 D-AOAC Moskva
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Old 27th May 2011, 20:59
  #186 (permalink)  
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Originally Posted by CONF iture View Post
1- AoA at 6 degrees and increasing + STALL warning
How is it possible the THS was still trimming up ?
What's wrong here ?
From GarageYears Link:
In Alternate Law, Valpha prot and Valpha max are replaced by VSW. Note that VSW is a stall speed and so is EAS sensitive unlike Valpha prot/max. Stick free aircraft aims to control alpha by limited authority stability order to less than VSW. If the stick input forces VSW exceedance, alpha floor activation of TOGA occurs. However, it is possible to stall the aircraft as the protection may be overridden.

Protections are as in Alternate 1 except that there is no bank angle protection in ALT 2 and in the case of failure of 2 ADRs, no VSW prot
So with the double ADR fail even Vsw prot would be lost thereby effectively losing basically all stall protection.

It has to be noted that Alt1+2 are Load Factor Demand laws with Auto trim.
So pulling Nose- Up sidestick command would cause Auto trim to trim Nose-up even above the stall.
I do not see anything indicating in the description of the laws preventing that in the situation AF was in.
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Old 27th May 2011, 21:01
  #187 (permalink)  
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Owing to the lack of meaningful disclosure by the BEA, speculation is fairly useless at this time.

It sure is interesting how the detail drops off after AP/AT disconnect and the zoom climb.
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Old 27th May 2011, 21:05
  #188 (permalink)  
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Different type (advanced autopilot, but no envelope protection), different set of inputs entirely.

If I remember correctly, what happened there was that immediately after selecting TOGA, the PF in that case felt that the climb gradient was too steep, so he instinctively pushed forward on the yoke to get the nose down. This led the autopilot to apply up elevator and trim to counteract the yoke force. The PF then re-applied forward yoke pressure and the AP responded again with opposite (nose-up) inputs. The oscillations this caused led to the aircraft pitching up almost to the vertical before control was regained.

What we have in this case appears to be deliberate nose-up commands applied by the PF in response to the loss of speed information - for reasons as yet uncertain. There was no autopilot to counteract those inputs as it had tripped out due to loss of speed data. Everything else that happened on the flight deck at this point is unknown, so all we know for certain is the trajectory the aircraft took. It's obvious that the BEA want to get this right rather than rush a report, so I for one don't see why we shouldn't let them get on with it - those that are complaining about lack of information at this juncture seem to be almost childishly impatient.
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Old 27th May 2011, 21:06
  #189 (permalink)  
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So presumably you'd have preferred the software to decide this wasn't allowed and roll off the trim - despite the input from the pilot demanding nose up? You really can't have it both ways now, can you? On the one hand half the crowd here are screaming for the head(s) of the software programing team for removing so much 'authority' from the crew, and here we have a request for the software to "decide" that the crew demand was unhealthy - even if it *was* unhealthy, are you sure you want additional laws and protections? Given that the aircraft has an auto-trim system, it appears to have been operating as expected, given the commands from the crew?
I understand that
Nevertheless the question was not about the first input .. but about a timing (3.5 minute)
3.5 minutes at 13° climb (about the max obtainable) position for the horizontal stabilizer with many other parameters complety jammed
How manage this by software (protection) is another story
Just a tought.
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Old 27th May 2011, 21:07
  #190 (permalink)  
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hello gents
a small question, does anyone know if any of the crew on this unfortunate had any time on older generation types? i dont want to start some sort of pissing contest but i do think the type of experience is relevent- lets not forget 5000hrs on one type is exactly that but 5k on 4 or 5 types must be worth 10k on on type yes or no?

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Old 27th May 2011, 21:09
  #191 (permalink)  
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Pitch up

Henra, maybe I got it wrong but I understood from the report that the aircraft was in a pitch up attitude of 16º when it reached 38.000 ft.

Level attitude would not be something around 4 or 5º ?

I understand that a good attitude indicator should indicate pitch variations of, at least, one degree. Sixteen degrees on the A-330 attitude indidator is not very noticeable?
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Old 27th May 2011, 21:10
  #192 (permalink)  
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Yellow Pen; I'm not in the aviation software business so I'm not familiar with the details of any particular aircraft system. I have some experience in software writing and crisis management. I'm just asking why the software would accept the THS being at its limit for so long.
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Old 27th May 2011, 21:11
  #193 (permalink)  
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The level of arcane systems knowledge this crew needed to dig up in the heat of battle in order to solve the riddle it was faced with is frightening. Having the return of the stall warning triggered by an appropriate control input would have been fiendishly difficult to comprehend under the circumstances. So sad that at this late date new knowledge of our craft is still being written in blood.
A simple question for Airbus pilots:

Until today were you aware that the stall warning could go away if a stall developed to the point that indicated airspeed dropped below 60KT?

And that it would return as you recovered?
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Old 27th May 2011, 21:14
  #194 (permalink)  
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Peter H
As someone with no aviation experience, can I ask how much a timely warning of [the likelihood of] UAS would have helped the pilots?
If it would have helped, perhaps more attention should be given to monitoring systems.
If cars can warn of hazardous road-temperatures, might not planes try to warn of ice-crystals.
As far as I can say, the requirements are very different: your car warns you about the external temperature, which would be useless for an airplane flying in an air mass at -50°C and below. The problem seems to be associated with ice particles having a very specific size; if they are smaller, they will be easily processed by the pitot heating system; if they are too big, they will not enter the pitot tube. Thus a suitable warning device would have to accurately predict ice crystals size in a timely fashion, say 20 seconds. With a plane flying at 300 m/s, that requires being able to monitor the size of ice particles having a diameter of a few millimeters as far as 6 km away, possibly through several layers of ice crystals having a different size. I can't imagine a way to do that with the technology currently available.
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Old 27th May 2011, 21:18
  #195 (permalink)  
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@ studi (#117 page 6) : Thanks for answering

Originally Posted by studi View Post
I was thinking of speed stability in Alternate Law.
OK so this one, I presume (*) :
"A nose up command is introduced any time the airplane exceeds VMO/MMO to keep the speed from increasing further, which CAN be overridden by the sidestick." (source)
My problem with accepting this hypothesis is that as far as we know, the indicated speed was not exceeding VMO/MMO. In fact, it was the contrary if the last BEA note is to be trusted.

(*) another (low) speed stability function exists, but this one commands a nose down input, not the case here.

Originally Posted by studi View Post
If we look at it from the other side, IF the plane was functioning normally, we would have a case of 3 pilots being TOTALLY inapt for their job, which I honestly can not even believe for Air France being the case.
Uh oh, I don't agree. They may have made a (fatal) mistake, i.e. not recognizing the situation. Are they to be called "totally inapt" for that? I'm not sure.
What were the conditions ? Why did they seem to loose all confidence in all of their "indications" (after having firstly correctly recognized a problem with the -sole- speed) ?
I don't know and some parts of the story are still missing.

MurphyWasRight's post #119 is for example very interesting with the stall warning on/off/on and the possible consequences of that on the PF's mind.
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Old 27th May 2011, 21:26
  #196 (permalink)  
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KMD - Apologies, I thought you were a pilot. I would speculate the software allows the THS to remain at it's upper limit because thats precisely what the pilot was commanding. There's got to be an approved upper limit to THS position somewhere, and if it's approved then having the THS at that position is not necessarily unsafe. There are numerous failsafes to counteract THS runaway or uncommanded movement, but if none of these failsafe triggers have been activated and the pilot is commanding nose up THS movement then as far as the machine is concerned it's situation normal. When an Airbus enters alternate law it's because the computers don't have sufficient information to reliably keep the aircraft within the normal flight envelope protections. I would suggest the more sensible option in that situation is to err towards greater control authority for the pilot.
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Old 27th May 2011, 21:27
  #197 (permalink)  
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center of gravity

Would that stall happen (the plane having no aft-forward velocity before a "natural nose down") with a "more forward" CG ?

I mean: Wouldn´t the plane go nose down before the a/c aft-forward speed got so low even with the HS trying a "pitch-up" if the cg was properly set ?
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Old 27th May 2011, 21:29
  #198 (permalink)  
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  • China Airlines Airbus Industrie A300B4-622R, Nagoya Airport April 26, 1994
  • Bournemouth Airport, U.K. - A Thomsonfly (now known as Thomson Airways) Boeing 737-300 with 132 passengers on a flight from Faro in Portugal to Bournemouth in England, September 2007
  • An Air New Zealand Airbus A320-200, registration D-AXLA (ZK-OJL), test flight GXL888T from Perpignan (France), Nov 2008
  • Turkish Airlines Boeing 737-800 at Amsterdam's Schiphol Airport, February 2009

etc etc All aircraft which crashed (or very nearly so) because the pilots failed to realise that the trim had been set full nose up, and couldn't understand why they lost pitch control.

Generally airline stall recovery training doesn't use or show a set up with the trim set this way - it is usually an artificial "OK, we are going to stall ... disengage the autopilot and slow the aircraft down, and stop trimming to allow for the recovery..."
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Old 27th May 2011, 21:30
  #199 (permalink)  
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It sure is interesting how the detail drops off after AP/AT disconnect and the zoom climb.
Don't forget there is a judicial enquiry engaged: maybe communicating too much info about the cockpit conversations could be considered a violation de l'instruction (early disclosure of judicial information) ?
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Old 27th May 2011, 21:34
  #200 (permalink)  
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Who knows what was happening in the office (cockpit). Unreliable airspeed indications, stall warnings and watching the altimeter winding down.

My feel is the overwhelming urge to pull up to address the reality of loss of height.... being led to believe they must be in a dive, not dropping like a brick due to being held in a stall.

No time, confused data and three pilots possibly adding to the confusion.
We grieve for all on board.
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