Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

AF 447 Thread No. 5

Tech Log The very best in practical technical discussion on the web

AF 447 Thread No. 5

Old 3rd Aug 2011, 22:28
  #1461 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
Dozy "Well, this is the thing - we've had two explanations doing the rounds - one, that the stall warning is inhibited by a software setting and the other is that once the airspeed has fallen that low that the AoA vane no longer functions. No doubt we'll find out if one, the other, both or neither is true in the coming weeks and months."

Don't forget that with a very high AoA the airspeed indication is VERY spurious. You get some ram air into the drain and you get reduced air into the business orifice of the pitot. The AoA vane was probably working. And when the nose was 10 degrees down would have clarified the stall warning by showing the AoA was still way too high to fly.

(I suspect it would be wise to get that green line I've started harping about into your graph for thinking purposes. It may explain some of the cockpit psychology.)
JD-EE is offline  
Old 3rd Aug 2011, 22:32
  #1462 (permalink)  
 
Join Date: Jun 2009
Location: Germany
Age: 67
Posts: 782
@DozyWannabe

DozyWannabe
In Normal Law you are commanding *rate* of movement in the axis rather than deflection. The FCU will do whatever it deems necessary with flight controls and thrust to get you the rate you're commanding. As you progress down through the laws, channels move from rate to deflection. In that case, I don't think the amount of time you hold the stick in a given position changes the deflection, but obviously the longer you hold the stick in position, the more time that deflected surface has to act, same as any other aircraft.
Could you reflect on my post post1433.html, please?
After your above statement i´m the more interested.

DozyWannabe
Quote:
Yellow : Elevator movement commanded
Green : THS begins following movement (autotrim)
Unfortunately the inputs are never held long or forcefully enough for the THS to make significant movements (remember it took over a minute of nose-up to go from cruise settings to full-aft), and the nose-down elevators last for 10-15 seconds at most - crucially they are immediately followed by a return to nose-up
could you point me to the indication, that the THS is moving? THS is the blue straight line on the bottom?

But by chance, how should THS move when after 15 sec. of SS ND the elevator peaks max at -15°NU (the magenta line)? Would the THS start moving prior elevators move to the ND range? How long is SS ND and in what magnitude required to get the elevator in a ND position?

If i read your above statement from post1436.html correctly, then elevator should be in "deflection channel" as you name it? Why does the elevator move only to 15°NU, even distinctive ND SS inputs where present (also not over prolonged time).

I hope, i didn´t get on your ignore list.
RetiredF4 is offline  
Old 3rd Aug 2011, 22:34
  #1463 (permalink)  
bearfoil
Guest
 
Posts: n/a
Hi Dozy. I think those Notches are what I took to be sawteeth, earlier.

"Serrata" if you will. I noticed two things. First I believe you are exactly right, each notch shows a 'command'. Also, they register as one second intervals on the timeline. What do you think?
 
Old 3rd Aug 2011, 22:37
  #1464 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
Dozy "@JD-EE - I'm pretty sure that "Assiette" can refer to pitch or trim, but in this case I think it means pitch. If it is a valid trace then yes, the nose fell down, but I suspect not in a controlled manner. In any case, the THS position, along with that of the elevators meant that as soon as the nose was down it would immediately come back up due to aerodynamic forces."

Good, we're that far. Notice the correlation between the PF's nose up and the nose down the aircraft executed. What would that do to the PF's mind?

As a side not I vaguely remember some discussion back in 2009 about the aircraft's behavior if airspeed really does decrease well below stall. It might even have been in the context of place the plane in the air at zero airspeed. The conclusion was that the swept back wings would make the nose go down. The data presented from the FDR seems to indicate this is exactly what the plane did. ("Good plane", as she pats it on its metaphorical head.)

Could the pilot have had a problem admitting the plane was stalled even with the nose pitched down 10 degrees? It is very clear to me that the pilots were both pretty much mentally rejecting that #$)**#@_) stall warning. (Imagining irritated profanity in their thoughts.)

edit
(Is incidence emis par... the AoA? It looks like it. That would have been a GIANT clue.)
JD-EE is offline  
Old 3rd Aug 2011, 22:42
  #1465 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
bearfoil, look at the graphs again. Is the real root cause the lack of a real AoA indication in the cockpit? That is rather hard for pilots to mentally reject. The AoA warning was easy for them to reject after training that it CAN happen spuriously. There is a hardware (design) error for you to consider.
JD-EE is offline  
Old 3rd Aug 2011, 23:03
  #1466 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,182
Originally Posted by JD-EE View Post
Good, we're that far. Notice the correlation between the PF's nose up and the nose down the aircraft executed. What would that do to the PF's mind?
The PF's inputs towards full nose-up begin at 2:11:40 and he's back against the stops at 2:11:42. The nose-down pitch doesn't begin until 2:11:45 and reaches 10 degrees nose-down (the lowest point it will ever reach) at approx 2:11:55. I might be being daft, but I see no correlation.

On top of that, if I pulled hard back and the aircraft's response was to pitch down in short order, recall of my Air Cadet days would suggest I might be stalled.

Am I missing something?
DozyWannabe is offline  
Old 3rd Aug 2011, 23:05
  #1467 (permalink)  
bearfoil
Guest
 
Posts: n/a
Hi JD-EE, The real root cause of what? Look, I think it is fascinating, this discussion re: AoA, Culture, and snarky repartee, ad nauseum.

The fact remains, the stage was set at AutoPilot disconnect, it becomes ever more clear. If the pilots were right, they would have recovered, and if they had grokked STALL soon enough, they would have recovered. But they were wrong, and kept expecting NU to solve their overspeed problem. It is certain. (my opinion only)

Three qualified Pilots ignore STALL WARNINGS and input near constant NOSE UP. Not an Approach to STALL recovery, (This is Not Colgan for silly sakes), and their mistake is clear to the hangers on, after the fact, Regardless the conclusion!

The initial PF saw Nose Up, Roll Left. The last one, Also PF saw Nose Up, Roll Left. None of the Pilots, NONE, grokked STALL.

Are you Pilot? High altitude, cruising, 500knots TAS. AP quits, must hand fly. Too much hand, a climb, a big climb. After Topping out, immediately see huge loss of altitude, and noise like you would not believe. Having heard one "bogus" fart from 447, I have huge airstream din, huge and continuing LOA, and I say "I think we have crazy speed!" They've seen UAS, so he isn't saying "Duff speed" he is saying "Way Fast".

There is no other way to see this, except to claim the boys were idiots.
That is perhaps the looniest opinion in two years of being here. Because there are some armchair pilots here (guilty) and pilots being who they are, everybody has a handle on it. The case is all but closed.

Nonsense.

See #1448

Thanks for all your input, I've learned much from you fund of expertise, and your way of presenting it.
 
Old 3rd Aug 2011, 23:21
  #1468 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Hi JD_EE,
Originally Posted by JD_EE
we've had two explanations doing the rounds - one, that the stall warning is inhibited by a software setting and the other is that once the airspeed has fallen that low that the AoA vane no longer functions.
There is only one single and simple explanation:
If no alpha_probe real failure is declared and no particular phase inhibition is declared:
1) - Stall Warning alarm is working provided that at least one ADR_alpha_channel is valid. (e.g. turning OFF all ADRs imply that Stall Warning alarm is totally lost).
2) - ADR_alpha_channel is valid provided that its own ADR_airspeed_channel is > 60 kt.

Consequently, if all three ADR_airspeed_channels are < 60 kt => case 1) Stall Warning alarm is lost.

But, this may become circular:
If alpha increases and is reaching a very high level, pitot_probes starts to under-read airspeed (due to angle of airflow related to ram tube orientation). At one point, alpha can be so high that airspeed is falling under 60 kt, causing alpha_probes to display NCD (invalid) values, causing the complete loss of Stall Warning alarm.

Consequently, the measured airspeed could be < 60 kt while aircraft is actually flying at 100+ kt but at very high alpha. Hence, high alpha will cause invalid alpha and Stall warning alarm will drop off at much higher airspeed than designed.
takata is offline  
Old 3rd Aug 2011, 23:21
  #1469 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 77
Posts: 1,330
@bearfoil;

You are dealing with a "cultural problem", and it is indicative of some attitudes that have developed over the last 40 years - or so.

This excerpt from an email, received from a French lady a few hours ago, may provide an insight into what I suspect you already know.
Do you know much about french-style education post 1968? Taking of initiatives, thinking for oneself, individual responsibility, curiosity of all things, CHECKING facts - have been deliberately educated out, the automated response and the supposition are supreme, the group action favoured. A few years ago government announced its intention of trying to return to the responsible individual attitude; put back the "jagged edge" which is the glue safeguarding democratic society, but which the unthinking have difficulty encompassing. It will be hard with more than two generations brainwashed. And then there are the "grandes écoles".

My Lebanese (but passionately pro de Gaulle) companion used to say of the French: "all the gear and no action".
Now, don't get me wrong! I'm not starting a "cultural" war.
mm43 is offline  
Old 3rd Aug 2011, 23:23
  #1470 (permalink)  
 
Join Date: Feb 2001
Location: right here inside my head
Age: 61
Posts: 178
Bearfoil,
With respect,
Originally Posted by Bear
Are you Pilot? High altitude, cruising, 500knots TAS. AP quits, must hand fly. Too much hand, a climb, a big climb. After Topping out, immediately see huge loss of altitude, and noise like you would not believe. Having heard one "bogus" fart from 447, I have huge airstream din, huge and continuing LOA, and I say "I think we have crazy speed!" They've seen UAS, so he isn't saying "Duff speed" he is saying "Way Fast".
The man with his hand on the stick [PF] should have realized early on that, if that were the case, the aircraft would respond MUCH differently to his inputs. I seriously doubt that many pilots I've ever known could mistake the one for the other [stall - overspeed] after even a moment at the stick, even while blind.

Also, there were not 3 pilots mistaking that for most of their fall... only the one. At best the PNF had a few moments to explore it himself, but not the Capt.

In an earlier post you alluded to people calling them morons... I haven't heard that from anyone yet, have you? I doubt even the most myopic among us would deny that at worst, they were at the mercy of their training, SOP's and a damned difficult situation.
3holelover is offline  
Old 3rd Aug 2011, 23:41
  #1471 (permalink)  
 
Join Date: Jun 2009
Location: somewhere
Posts: 451
In english

English version
A33Zab is offline  
Old 3rd Aug 2011, 23:43
  #1472 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 80
Posts: 1,689
Originally Posted by takata
If alpha increases and is reaching a very high level, pitot_probes starts to under-read airspeed (due to angle of airflow related to ram tube orientation).
Correct, but don't forget that static pressures are affected also, reading high. Pitot minus static can become negative in extreme cases, as mentioned in one of the BEA reports.
HazelNuts39 is offline  
Old 3rd Aug 2011, 23:52
  #1473 (permalink)  
 
Join Date: Jan 2006
Location: Dorking
Posts: 472
Bearfoil

This will get deleted soon, I'm sure.

Bearfoil might be a Civil Engineer. They all fell asleep during Fluid Dynamics lectures on my degree course.

Not many months ago he was certain that the tail had fallen off. Mainly because it was made in Europe. We don't do glue as well as the Americans.

Put him on your ignore list. Worked for me.

The frustration rises when I see him quoted.

Hope this doesn't get me banned?
boguing is offline  
Old 3rd Aug 2011, 23:54
  #1474 (permalink)  
 
Join Date: Jun 2009
Location: California
Age: 51
Posts: 203
Bear
IMHO they were convinced of overspeed. Nose up, give me all the stick back you got, why does she stop at pitch +16 deg, I want more. Deploy spoilers. Idle the engines. Crazy speed.

What made all three believe in overspeed. To the extent that they can ignore stall warnings, the UAS procedure, ignore the high pitch, low IAS, low ground speed, ambient noise changes. Was it the deceleration giving them the perception they were in a dive and PF thought the attitude indicators were wrongly showing +16.
Something made them all convinced of it. Did the PFD show the red black overspeed ladder?
Even a sceptic has to wonder if there was something else they saw that we do not.
I might believe one or maybe 2 had it totally and insanely wrong but not all 3 pilots.
xcitation is offline  
Old 3rd Aug 2011, 23:55
  #1475 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,182
Originally Posted by RetiredF4 View Post
If i read your above statement from post1436.html correctly, then elevator should be in "deflection channel" as you name it? Why does the elevator move only to 15°NU, even distinctive ND SS inputs where present (also not over prolonged time).
I can't answer for sure, but I have a feeling that the trace in the FDR describes elevator position relative to THS position. I hope someone else will confirm/refute this, but if you compare the SS traces, the elevator traces and the THS traces it seems to make sense.

I hope, i didn´t get on your ignore list.
Franzl, I've never put a single person from a single forum of which I am a member on ignore list in my life! I'm quite capable of mentally filtering out waffle if I need to, and I've always operated under the assumption that even people who get on my nerves probably have something to teach me, so it would be ignorant of me to ignore them.

And even if I did - you're a long way from anywhere near the list that I'd contemplate putting on ignore!
DozyWannabe is offline  
Old 4th Aug 2011, 00:07
  #1476 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Hi HazelNuts39,
Originally Posted by HazelNuts39
Correct, but don't forget that static pressures are affected also, reading high. Pitot minus static can become negative in extreme cases, as mentioned in one of the BEA reports.
Yes Sir! ... high alpha affects every probes, including, static and alpha probes!
Hence, airspeed is twice affected (did you try to derivate aircraft actual airspeed from ground speed and other parameters to see at which estimated (true) value airspeed was reading under 60 kt ?)
And V/S is also affected (obvious from graph)... and somewhat baro altitude...

This limitation of +60 KCAS for alpha validity would be due to good reasons, but I don't know which one... it seems to me easier to inhibit this alarm during specific phases when you don't need it (ground, rolling...) than doing it this way in relation with airspeed.
takata is offline  
Old 4th Aug 2011, 00:36
  #1477 (permalink)  
 
Join Date: Oct 2007
Location: France
Age: 69
Posts: 136
Originally Posted by Shadoko
Think correct translation in English of aeronautic use of "gauchissement" is "wing warping".
Originally Posted by ChistianJ
Sorry... but you're wrong, unless you're talking about the "Wright Flyer" and aircraft from that age..
It may well be the logical original 'source' of the term in French aeronautical terminology, but today it just refers to "roll" or "roll angle".
Thank you for the correction. The word have been discussed without clear answer, so I tried with dictionaries : no knowledged people under hand ("lost" in the meddle part of France).
I understand you have a very fine knowledge of aeronautical wording, both French and English. If you do not mind, could you say what you think of AF447 conversations as they are transcribed (wording, technicity,...)? I am very surprised by them (but have no knowledge at this), even if there were an understandable "stress". When compared with those in the cockpit of the Airbus which landed on the Hudson (supposing the YouTube retranscription is valid: wwwDOTyoutubeDOTcom/watch?v=tE_5eiYn0D0). And if you don't want, for any reason, to write about that, I would understand. Thanks anyway.
Shadoko is offline  
Old 4th Aug 2011, 00:40
  #1478 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 80
Posts: 1,689
Originally Posted by xcitation
What made all three believe in overspeed.
The altitude tape scrolling down at an unusual rate, the 'vario' at the negative peg?
HazelNuts39 is offline  
Old 4th Aug 2011, 00:57
  #1479 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Hi mm43,
Originally Posted by mm43
This excerpt from an email, received from a French lady a few hours ago, may provide an insight into what I suspect you already know.
Your French lady's statement and her view on French "society" seems seriously connoted!
It should be taken it with a (big) grain of salt, excepted, maybe, the quote from her Lebanese (nonetheless pro-De-Gaulle) companion!
takata is offline  
Old 4th Aug 2011, 01:17
  #1480 (permalink)  
 
Join Date: Mar 2006
Location: England
Posts: 868
GarageYears, re #1451
“I suspect you are not really accepting that the system designers have generally NOT considered the region deep into a stall.”

Quite possibly; particularly in the manner in which it is being discussed in this thread.
Certification considers a locked-in deep stall from aircraft geometry aspects, as with a ‘T’ tail, but the A330 stall appears to be ‘locked-in’ due the control system, predominantly trim holding a pro-stall condition. Certification, be it right or wrong, considers that the control condition should not be considered, or if so it is recoverable by crew action


Certification flight tests will examine all aspects of an aircraft’s stalling characteristics, including searching for a ‘deep stall’ on geometrically susceptible aircraft. However, the tests may not evaluate an extreme mis-trimmed condition outside of the normal flight envelope.

Modern designs aircraft have moved toward ‘preventative’ systems. Some stick pushers which I have flown should not to be argued with - high forces, but as in your example, a fearful pilot can overcome such systems. Thus the digital trend is towards avoidance / limiting, but as is being discussed this may not cover all non-normal conditions.
The probability of protective systems failing together with stall AOAs and mis-handling the aircraft clearly exceeds the probabilistic certification assumptions. This is ‘black-swan’ territory where the industry depends, either consciously or not, on the human rescuing the situation.
We celebrate many notable successes. Unfortunately we have to suffer failures; this hurts our pride, beliefs, and our professional standards, and correctly we search for a solution, but as I questioned earlier, do we understand the problem – all aspects of the problem.


I agree that we are bombarded by technology, automation, etc, but adding more to ‘encase’ the pilot will only increase the complexity of an already over complex operational environment.
If technology is to help then it should be in a form as you suggest, releasing the pilot from the technological cage and encouraging cognitive excellence; but if this is achieved via technology, we still have to consider what happens when that technology is unavailable.
In such circumstances the human is still best placed to evaluate and judge the situation; but the human might benefit from some generic skills training to improve awareness, managing surprise, and knowledge recall; aspects of higher professional standards perhaps.
PEI_3721 is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.