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AF447 final crew conversation - Thread No. 1

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AF447 final crew conversation - Thread No. 1

Old 26th Oct 2011, 11:35
  #401 (permalink)  
 
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Originally Posted by Capn Bloggs View Post
The purpose of washout (look at the outboard 1/4 of a 747 wing from the rear) is to prevent this entire-wing-stall-at-the-same-time. The entire wing won't stall "at the same time", surely?
Yes absolutely. But if any part of the wing stalls it still has the effect of moving the centre of lift forward purely because of the separation of the airflow from the rear of the wing section.

My 'entire wing' thing was just an example of that.

A deep stall can be induced on any aircraft with enough elevator authority or as a result of design. Recovery from a deep stall can be harder to achieve if the elevator then becomes less effective as per T-Tail aircraft or some other configuration.

Considering that AF447 AoA was somewhere between 35 and 60 degrees you can surmise that the horizontal stabiliser also had a similar AoA, effectively the HS was also stalled. If they had made a large nose down input to attempt recovery that would have the effect of increasing the AoA of the HS past 60 degrees. Coupled with TOGA power I suspect the effect of the ND input would have been negligible.
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Old 26th Oct 2011, 12:16
  #402 (permalink)  
 
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If they had made a large nose down input to attempt recovery that would have the effect of increasing the AoA of the HS past 60 degrees. Coupled with TOGA power I suspect the effect of the ND input would have been negligible.
In that case, pull one throttle to idle, give it a handful of aileron and a boot of rudder to get it into an incipient spin, then recover to flying speed with full forward stick.
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Old 26th Oct 2011, 12:53
  #403 (permalink)  
 
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The "then recover to flying speed..." part, though sounding good, appears to have at least the potential to be a bit problematical.
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Old 26th Oct 2011, 12:59
  #404 (permalink)  
 
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Originally Posted by OK465
appears to have at least the potential to be a bit problematical.
Got any better ideas?
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Old 26th Oct 2011, 13:09
  #405 (permalink)  
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You are all ignoring the nose down pitch change that occurred each time nose down elevator was applied?
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Old 26th Oct 2011, 13:16
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BOAC indeed +1
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Old 26th Oct 2011, 13:20
  #407 (permalink)  
 
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Was there a significant trend of AOA reduction with the pitch changes?
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Old 26th Oct 2011, 13:29
  #408 (permalink)  
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Have you actually looked at the FDR trace? Tell me what you think.
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Old 26th Oct 2011, 14:07
  #409 (permalink)  
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Nose drop with back stick is a classic stall indication taught at the PPL stage.

I don't think Flap 1 is used for stall recovery. It is, I believe, in the QRH POST stall recovery. However, if nothing else is working, most pilots would (I hope) try lots of things including gear down.
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Old 26th Oct 2011, 14:42
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And at no time did the AOA get below 35, but this of course may be a matter of magnitude & duration of ND inputs. I wish I knew.
Note that even during the two attempts at ND inputs the elevators only reduced from 30 deg to 15 deg up, they never even got to down elevator...
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Old 26th Oct 2011, 14:58
  #411 (permalink)  
 
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Very true, and as AZR stated, we don't 'ACTUALLY' know the effect of a positive ND SS input, because they never got there.

It is one possibility that a stall recovery could have been achieved, but not a certainty. I would prefer to see the final report rather than make assumptions, regardless of how well founded they seem to be from experience with previous or other aircraft flown.
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Old 26th Oct 2011, 15:50
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Clandestno.....fantastic post:
Well, we're out of prejudices here as it happened to long established western flag carrier. Most of the posters feel that it struck close to home and they can not write it off easily as something-that-can't-happen-to-me. Mental gymnastic they perform to deal with their shock and horror is very interesting thing to behold but its results are not particularly informative.
True, what also doesn't sit well is the fact that the plane just fell out of the sky in a stall. The tail didn't tear off, the engines didn't fail, there was no "act of God"...

I have been reading the AF447 threads since day one and have absorbed every conceivable scenario pointing towards some sort of aircraft malfunction. This obviously would have been an easier way for people to digest and understand what had happened.

But from what we know so far...it seems two qualified pilots became disorientated, didn't correctly address the situation, and foundered without fully understanding they were in a stall....

That is hard to deal with, and adds to the depth of the dilemma of trying to comprehend this disaster.

This is everybody's nightmare: pilots, passengers, manufacturers, airline companies....and it isn't going away...

Last edited by Razoray; 26th Oct 2011 at 17:52.
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Old 26th Oct 2011, 16:01
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This is everybody's nightmare: pilots...
It's only a nightmare for me because some expert has told me I can no longer practice what probably would have saved their lives: flying the aeroplane. I don't care what it is: a gentle turn here and there, a raw data ILS on a gin-clear day with no traffic, it all helps me to get in tune with the machine and hopefully, when things to go completely haywire, I'll have the skill to assess and react correctly. An auto-trim design doesn't help, of course.

Originally Posted by OK465
seems preferable to a spin
Don't get me wrong; I am not suggesting spin it, just "upset" the upset to break the status quo. Incipient is the word I used.
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Old 26th Oct 2011, 16:05
  #414 (permalink)  
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Yet again we are seeing a thread that is out-performing the Oozlum bird.

Here we are, over two years of time to digest, argue, prove that (supposedly) type-qualified pilots don't understand it, look at FDR traces, see CVR transcripts - and we still don't really understand what happened.

We have two fairly inexperienced lads, and an experienced Captain, who presumably have been told that this a/c will protect you from cradle to grave (!!) and cannot be stalled and that one 'OK' thing to do when in difficulty is to put on full power and pull back the Sidestick - and she will sort it out. 'She' didn't. To make matters worse, when they relax the back pressure, it tells them it is stalling again. Is it any wonder they were confused?

What is apparent is that auto-trim contributed to this accident as it also did in PGF when it trimmed in manual flight and the 737 at SPL. when it trimmed in A/P.

If, apart from training issues, nothing else comes out of this I would hope that as I said after each of these three crashes - there HAS to be a point at which the trim system stops at some pre-determined value and ASKS for confirmation that what it is doing is what is wanted, particularly in the AB types and the newer Boeings where trim operation is 'un-noticed' - 'silent - but deadly'?
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Old 26th Oct 2011, 16:07
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Doesn't auto trim stop when you go below Vls? The worry for me isn't that they couldn't get out of the stall but that they got it there in the first place!
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Old 26th Oct 2011, 16:11
  #416 (permalink)  
 
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Oozlum Bird. Good one BOAC.
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Old 26th Oct 2011, 16:22
  #417 (permalink)  
 
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Originally Posted by OK465
Does the Velocity stall description bring anything to mind?
Of course it does! It reminds of my snide remark that mental gymnastics some posters apply are awesome to behold while being of poor to nil informational value.

I don't mind stressing for the third time: we're discussing the deep stall as related to transport category aeroplanes and as is described by DP Davies, certainly an authority in the field of transport aeroplanes behaviour. Reference is "Handling the big jets", pages 115-119 in the third edition.

Velocity is four seater aeroplane. A330 is not.

Velocity is piston powered aeroplane. A330 is not

Velocity is single engine pusher aeroplane. A330 is not

Velocity is canard aeroplane. A330 is not.

There are also some differences between Velocity and A330 regarding the mass and wing loading.

To just wink-wink-nudge-nudge-you-know-what-I-mean in order to somehow make an impression that something that Velocity's test pilot has encountered during test flight and was labeled by NTSB as deep stall has anything to do with transport aeroplane's deep stall and therefore further imply that Velocity incident somehow proves that A330 is susceptible to the phenomenon is beyond my ability to comprehend. Why would anyone mix handful of facts with bag of suspect notions and expect to get something meaningful out of it is enigma to me.

If we'd call every extremely high AoA situation deep stall, there would be no end of it.

Originally Posted by Lord Spandex Masher
I can't, I have paper copies of several flight test documents on controls and stability.
Why? Because you would have to kill me if I see it? Can't you at least hint what aeroplane is dealt with in your papers or someone would get you if you release that little bit of information?

References contrary to your claim can be found in "Handling the big jets". third edition, page 119. Or any decent basic aerodynamics textbook, e.g. Atlantic Flight Training ltd JAA ATPL training handbook, Principles of flight, pages 8-14 to 8-16 in 2006. edition. Those were first that I dug out of my bookshelf and I can't publish excerpts due to copyright issues but if you really want to know what's written in them, i don't think you'll have problem finding out.

Originally Posted by Lord Spandex Masher
It is not the tendancy of a T-Tail to deep stall it is the recovery that can be a problem
You were on good way to tautology before you slipped into something akin to surrealism. Of course that recovery is the problem! The biggest part of the deep stall definition: it's irrecoverable!

Originally Posted by Lord Spandex Masher
Even if the entire length of a wing, swept or straight, stalls at the same time the separation of the airflow occurs towards the rear of the wing causing the centre of lift to move forward. Unchecked that may cause pitch up.
(...)
But if any part of the wing stalls it still has the effect of moving the centre of lift forward purely because of the separation of the airflow from the rear of the wing section.
But it doesn't follow that moving the Cp in stall forward results in pitch-up! If it were so in the real world, we would be in deep trouble and I certainly would not be writing this post but pushing daisies at certain quiet village graveyard.

Originally Posted by Lord Spandex Masher
Did you not spot the part about several roll excursions, some up to 40 odd degrees and the 270 heading change?!
These roll excursions started when aeroplane was extremely deeply stalled. Whether they were stopped by CM2's monstrous effort on the stick or by sheer incident is something for aerodynamicsists to resolve. Aeroplane has stalled somewhere around 02:11:06 Z. Next 30 seconds roll is quite gentle, not exceeding 9 degrees. AoA increase is also gradual and that is somewhat at odds with the theory of tips stalling first.

As for 270 turn, I find it quite astonishing for diametrically oposite reason to you: that it was so mild. 270 over three minutes gives astonishing average of 1.5 per second or four minutes to complete single turn. Now I'm only waiting for the next ignoramus in line to state that it was Airbus fault that aeroplane which was never intended to have good post-stall characteristics had so benign stall and if it spun (as B752 at Puerto Plata did) the pilots would have at least an idea what was wrong.

Originally Posted by Retired F4
I raised that question (how would the FCPCs behave during manual trim when not in direct law) some moons ago. Nobody followed my lead there.
Reason for it might be that I don't recall this information being included in FCOMs, I remember it as part of my training syllabus. When my captain & me went on Airbus 320 TR course, it was for both of us our first MRJT so our company thought it was good idea to put us through something called "Jet transition" It was ten hours of raw data, manual flight in direct law without autothrust for each of us. Direct stick-to-control displacement. Normal pitch-power couplings. Trimming with the wheel all the time. It certainly gave us the feeling what is the aeroplane like to fly without FBW holding your hand. Contrary to horror stories we heard, after ATR it was piece of cake. Near the end of jet transition, ALT law was introduced to give us taste of autotrim and that's when we were demonstrated why it isn't good idea to fight the autotrim - to make sure there's no negative transfer from "Jet transition" into "Normal" phase of training which was conducted in normal law. It didn't come cheap - we have used up 20 hours of sim time and prolonged our course by a week. So did it pay off by making us better A320 pilots than we would be if we just started with full FBW and making just casual acquaintance with direct law during abnormals? It's just my severely biased opinion but I'd say - hell, yes!
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Old 26th Oct 2011, 16:25
  #418 (permalink)  
 
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OK.....here I am.....again. Why can't we all just admit that if this had been a "conventional" airplane [cable-operated, not computer/electric-operated] that we would not even have a thread on this? #378
Not Necessarily

Narrows, Virginia; ABX Air (Airborne Express) DC-8; December 22, 1996

"probable causes of this accident were the inappropriate control inputs applied by the flying pilot during a stall recovery attempt, [and] the failure of the nonflying pilot-in-command to recognize, address, and correct these inappropriate control inputs . (Summary)"

"... the airplane remained in an aerodynamic stall condition because the PF held significant back pressure on the control column all the way to impact.(2.2.1)"
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Old 26th Oct 2011, 16:33
  #419 (permalink)  
 
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BOAC writes

You are all ignoring the nose down pitch change that occurred each time nose down elevator was applied?
Isn't it possible that only happened because of the full up trim? eg it was full up trim that was preventing the THS from stalling.

Had they wound in nose down trim it might initially have caused some nose down pitch but would it have been enough to keep the THS from stalling as the up trim came off?
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Old 26th Oct 2011, 16:52
  #420 (permalink)  
 
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CLANDY: Thank you for sparing us the pictures this time.
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