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AF447 Thread No. 3

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AF447 Thread No. 3

Old 27th May 2011, 15:27
  #81 (permalink)  
 
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There is a F/CTL STAB CTL FAULT procedure.

It basically says to use the Pitch Trim wheel.

One of the subsections reads: If trim is locked above 8 degrees UP, pitch down authority may be insufficient for speed above 180 knots.
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Old 27th May 2011, 15:30
  #82 (permalink)  
 
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... or simply being constantly told during training "You can't stall an Airbus." as an absolute statement, reinforced by full back & side stick climbs at the lowest possible speed in the simulator to demonstrate "How the aircraft won't let you stall
That might be an (far fetched) explanation for the initial pitch up. Maybe the PF had a reflex action and applied a kind of windshear/terrain avoidance maneuvre. But after a few seconds it should be clear that that is not working.

I wonder in what state the aircraft was when the AP dropped out. Was it pitching down, or up? That's crucial information.
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Old 27th May 2011, 15:35
  #83 (permalink)  
 
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Originally Posted by checkboard
No - for any aircraft with this configuration, the stabilizer is more effective than the elevator, and easily overpowers it, especially with the added pitch up moment from high thrust.
Thanks for the reply. I agree with your basic answer - although I would not go so far as to say "any aircraft" .

I presume you are AB330 qualified therefore, second question:

The BEA release (which I have now read) seems to indicate that the position of the THS was +13 deg. (nose up).

Question: On the AB330, what is the maximum nose up deflection of the THS? Might it be +13 deg or anything close to that?
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Old 27th May 2011, 15:41
  #84 (permalink)  
 
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No indication that the airspeed on the PFD was inaccurate. Just that after it went out of range, the PFD came back about a minute before the standby. They were close to max cruise alt, got a stall warning and zoom climbed to 38000.
On first reading this doesn't look good!
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Old 27th May 2011, 15:43
  #85 (permalink)  
 
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Not A330, but A320 series qualified. On that type, the THS limits are 13.5 nose up and 4 nose down.
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Old 27th May 2011, 15:47
  #86 (permalink)  
 
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Originally Posted by PENKO View Post
Dozy, I would not dare to say that yet, the report is very unclear. It feels as if we are presented only half the information.
Just to clarify - I wasn't suggesting that's what happened, I was responding to your question as to why a pilot approaching stall would pitch up suddenly in that manner. All I meant by the example was to show that pilots have done it before.
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Old 27th May 2011, 15:48
  #87 (permalink)  
 
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Checkboard

Thanks for the AOA post - never flew the bus.

BOAC
regarding pilot pulling back on the stick with a stall
- seen it but not on an airliner - it is a natural reaction to a falling sensation as is sticking out a hand which leads to a broken wrist.

Re; simultaneous stall and overspeed warnings for the non ATPL holders.
Three pitots and two static sources - depends on timing and sequence of freezing up.

Similar to the Trident crash;
the crew would have faced many simultaneous aural and visual warnings.
it would be very confusing.

The philosophy at the time of the trident crash was that if the stick push fired then dump it as it would be a malfunction.

I can understand with the bus design philosophy of not being able to stall the bus that the crew disbelieved the stall warning.

One question that has not been addressed is whether the horizon on PF side was indicating correctly?

I doubt if we will ever know what the pilots were looking at.

ITCZ 12o heading change - quite normal - it's like flying through a bowl of tapioca with different sized lumps.

hopefully we will one day have 24/7 data links with all parameters including video - I suggested video for sim checks 20 yrs ago and was told why?
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Old 27th May 2011, 15:50
  #88 (permalink)  
 
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Old 27th May 2011, 15:50
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Can you tell what the other guy is doing?

Simple question, how easy is it with the side stick to know what inputs the other guy is making?
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Old 27th May 2011, 15:50
  #90 (permalink)  
 
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@Checkboard:
From a training briefing dated 1999 on Airbus 330. I don't know if Airbus has changed this. Looks similar to what you are familiar with.

"Pitch control is provided by two elevators and the THS :
- elevator deflections 30 nose up - 15 nose down
- THS deflections 14 nose up - 2 nose down."
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Old 27th May 2011, 15:54
  #91 (permalink)  
 
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Where on earth has this idea that you can't stall an Airbus come from? It's made perfectly clear during ground school before you even get near a simulator that you can stall the aircraft, and you will stall the simulator during training. What is more of a concern is the full left and nose up sidestick input, something which would not be evident to the other pilots.
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Old 27th May 2011, 15:55
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Originally Posted by Svarin
In the Perpignan accident, manual pitch trim was not used.
In this accident, it would appear it was not used either.
Perpignan was a test flight where they tried to kick "Alpha prot-Alpha max" at low altitude with defective AoA probes. They had no time to recover from FL380 like AF447 was. I think I do remember that those test pilots crashing in Toulouse (1994), very close from recovering from a low alt LOS with an engine stopped on test purpose, used manual ths trim. But what would be the point if they did? They would have been authorized and any other pilot forbidden.

Originally Posted by Svarin
The fact that the manufacturer left this manual pitch trim wheel in the cockpit does not exclude the fact that in real life, in real airlines, on board real airplanes, pilots are actually taught not to use it, and never use it, according to design.
Right, of course: it is like having a "direct law" with only manual THS trim available, with a message poping up and saying "Manual pitch trim only"... WTF!!! I won't ever use this [email protected] or I'll be fired!
Your position doesn't make sense: it is not "per-design", it is not "forbidden": it is always better not to have to use it (like being in normal law instead of direct)... up to the point that you need it!
Now, how training is performed is a different issue.

Last edited by takata; 27th May 2011 at 16:09.
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Old 27th May 2011, 15:56
  #93 (permalink)  
 
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I wonder what caused the first stall warning. Was it loss of airspeed or was it G-induced by the pilot trying to recover after the AP dropped out? After that warning they still managed to climb with 7000 feet per minute to FL380...
This was recovered by a nose down command, followed by nose up for the second stall warning.
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Old 27th May 2011, 15:58
  #94 (permalink)  
 
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Cool

Hi,

For those who understand french .. it can be interesting ...
A graphical chronology of the events commented in the BEA communication.... (from a french forum)
It's more easy to see the gap in time of no comments at all (shadow zones)

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Old 27th May 2011, 16:01
  #95 (permalink)  
 
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interesting similarities

One may want to compare this accident with Pulkovo Flight 612 accident:

- in both cases, aircraft stalled at high altitude when crossing severe turbulence;
- in both cases, pilots were perfectly aware of weather conditions and made attempts to avoid flying into the worst;
- in both cases, pilots were mainly pulling the stick (control column in case of Pulkovo 612) instead of applying proper stall recovery procedure until it was too late.

And yet:

- Pulkovo 612 was a Tu-154 aircraft, which is not FBW and is lagging almost 50 years behind A330 in terms of automation;
- One of the Pulkovo 612 pilots was a former aerobatic champion, so he probably knew something about stalls and stall recovery;
- Tu-154s have AoA indicators in cockpit, which provided meaningful and valid information throughout the accident. Also, pitots did not freeze and the airspeed indicators were also valid.

Yet it seems that in both cases pilots either did not recognize that the aircraft has entered fully-developed stall, or somehow failed to apply proper recovery procedure.

One can probably draw a conclusion that such proposed measures as "upgrading the pitots so that they never freeze" or "reducing level of automation" (whatever falls into that category) would not prevent such accidents from happening again.

Just my 2 cents.
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Old 27th May 2011, 16:07
  #96 (permalink)  
 
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Thank you very much, gentlemen (Checkboard, Garage Years, Lonewolf 50).

From your replys and the BEA release, I gather that the THS was within 1 deg. (+13) of its maximum nose up position - and approximately 5 deg. beyond the point at which it could be overcome by full nose down elevator (without changing THS angle). [Please correct me if this is wrong.]

One final question: Is the thrust line of the AB330 such that the application of TOGA thrust will induce a significant nose up (pitch up)moment?
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Old 27th May 2011, 16:07
  #97 (permalink)  
 
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Thanks

Wow! Super answers, and the Garage guy's reference is outstanding. Hell, I'm almost ready to try to fly the beast after a few more hours of study, heh heh. As a TV ad says, " it's so easy that a caveman can do it".

I raised the runaway trim issue, as many of us were taught to roll the plane if we had runaway nose up trim. The technique was intended to maintain a reasonable pitch attitude. For nose down, the idea was to reduce power/slow down in order to overcome the elevator trim. Of course those procedures were for "elevators" and not the horizontal stab.

As we try to digest the data and maybe cry a bit, I'll ad lib and add a war story about horizontal stabs. JT Moderator can delete if appropriate, but it explains a few things about many planes' horizontal stab designs.
++++++++++++++++++++++++++++++

So first few months at Hill we had all kindsa celebrities drop by the first Viper unit in the world. One was Chuck Yeager. And we all assembled in the main briefing room and he sat on the stage, feet on the floor, and told us war stories and answered questions. Was a magic moment, I tellya.

He got to the part about the first supersonic flight and a bit of advice from a Bell technician/aero dude. He told Yeager that once supersonic or even close to the mach that they were worried about losing elevator control due to the shock waves. So they had a manual wheel to 'trim" the horizontal stab. He told Yeager that if all else failed, to use that sucker and he might gain pitch control.

Sure enough, above the mach the elevators didn't work very well, if at all. So Yeager cranks the wheel back and forth and regains pitch control. Back below the mach all was "normal". He told us that this discovery was why North American and other folks developing the new jets went to the one-piece horizontal stab. Moving the entire thing as one piece changes the shock wave pressures and the thing acts like a "normal" jet.

Gotta love it!
++++++++++++++++++++

We now return to our regular hypothesizing and second-guessing, heh heh
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Old 27th May 2011, 16:12
  #98 (permalink)  
 
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Originally Posted by Checkboard View Post
... or simply being constantly told during training "You can't stall an Airbus." as an absolute statement, reinforced by full back & side stick climbs at the lowest possible speed in the simulator to demonstrate "How the aircraft won't let you stall."
You're forgetting the caveat "as long as the relevant protections are working", which is a pretty important one.

Originally Posted by takata View Post
Now, how training is performed is a different issue.
Agreed - there seems to be considerable confusion here between recommendations made by Airbus themselves versus how those recommendations are filtered down to airline training departments. If what Svarin says is true, then I'd say that's a pretty serious deficiency in that airline's training!

Someone asked me in the previous thread about what I meant by Airbus acknowledging some of the more lurid claims made about the safety aspects of the system in the early days were unhelpful, to which I'll say that their whole training and marketing syllabus changed tack dramatically in the 1990s. Rather than focusing on how easy the aircraft was to fly compared to more traditional aircraft, the focus changed to one of the systems "assisting" the pilot.
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Old 27th May 2011, 16:14
  #99 (permalink)  
 
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Wouldn't a warning help?

JPI33600
Apart from R&D work about how to prevent UAS condition, this seems to call for a better training of pilots in unusual situations.
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.

Regards, Peter

PS The more I think about a "flight engineer's console", the more it seems to complement the strengths of existing FBW systems.
For example, the u/s (but not 'faulty') RA at Schiphol could have been identified by sanity and/or consistency checks, and [manually] taken out of service.
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Old 27th May 2011, 16:14
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Originally Posted by eireoflot82 View Post
Could the physical sensation of a rapid descent combined with doubt about the veracity of the flight information and the lack of outside visual references simply trick the brain into misreading the situation they were in?
You don't feel descent, only acceleration. You will feel the initial downwards acceleration but once travelling at a steady speed there is nothing to feel.
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