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AF 447 Thread No. 12

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AF 447 Thread No. 12

Old 26th Feb 2017, 16:15
  #1361 (permalink)  
 
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"Disparate" was my word, I did not intend to imply you believed they were.

"Maintain" back stick? My comment was that back stick seemed not to be maintained, but was "choppy". I assumed that since you didn't direct me to the report, that indeed the report did not do the integration you suggested, and that I would have thought that the report should have done that, to educate those of us who are not geniuses?

I won't paraphrase you again, and I am sorry it irritated you.

Are autostabilized commands of any import to a conclusion about why the THS acted so?

If the THS continues to trim Nose Up, after the Stall, is that a "Protection"? It would seem counterintuitive that in a Stalled condition, the aircraft acted, automatically, against what might be considered "recovery" of aerodynamic flight?
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Old 26th Feb 2017, 16:54
  #1362 (permalink)  
 
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Another reference-Bruce Tognazzini on Panic

Bruce Tognazzini wrote this blog on panic some time ago. His specialty is software design however he is a pilot and diver as well.
Panic! How it Works and What To Do About It
Suggest you follow the link before reading the rest of this paragraph.

This particular paragraph explains what I believe happened to the crew of AF447 right at the beginning of the event:
The natural role of the anxiety leading to panic appears to be to guide us toward immediate evasive action, be it flight or fight. Panic ensues when we are unable to formulate an effective evasive action, we choose the wrong evasive action, the evasive action is ineffective, or the evasive action goes terribly wrong in ways we do not understand.
From this, we see that development of the panic state is a two step process.
  1. Activation of the Fight or Flight response
  2. Inability to formulate/execute an effective evasive action.
This parallels the initial AF447 experience:
  1. Autopilot drops out inside a turbulent cell while crossing the ITCZ=Activation of Fight or Flight
  2. The aircraft roll response is strongly stimulated by the PF's initial correction and he cannot get it quickly under control as it continues to oscillate in roll= cause for panic.
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Old 26th Feb 2017, 17:40
  #1363 (permalink)  
 
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As I said, the THS takes its commands from the elevator position. Look at Fig.63 of the report. When the THS was moving towards a NU trim the elevator was ALWAYS negative (nose up command). I assumed you had read the report.
However, I think you are using the report in an unintended manner. I believe accident reports are written to inform not to educate.
The autostabiliser commands are in this case relevant only to reinforce the point that one cannot judge the THS movement solely on the basis of stick position.
Of course the THS movement seems counterintuitive, but the THS control system knows nothing of the aircraft's stall state. I repeat, it only reacts to the elevator deflection it sees. In this case the elevator was driven almost entirely by the pilot's command, the contribution from pitch damping being very low as the pitch rates were very low. In normal law of course it would be a different story and the THS would be prevented from further NU movement by the down elevator applied as stall protection.
As Machinbird said in an earlier post, the puzzle is why NU movement was not inhibited in alternate law when stall protection became active.
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Old 26th Feb 2017, 17:51
  #1364 (permalink)  
 
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Protections lost....

Thanks for being patient. My understanding is that the report is written and published "to the public".... I don't consider it overly technical, but my expectation is that any "study" undertaken in the investigation would not include "assumptions should be made when the study is incomplete?"

So I consider the THS "study" incomplete.

You state:

"As Machinbird said in an earlier post, the puzzle is why NU movement was not inhibited in alternate law when stall protection became active."

At the risk of tarnishing my non genius status further, aren't "protections lost" in alternate law? IOW, what does "when stall protection became active" have to do with this initial, and ultimately unrecoverable Stall?

And in discussing this wreck, how can the pilots be at fault?

I have to be missing the plot.

Thanks

jmo

(When AP, AT, FDs, and other automated systems are lost, why would one "Automatic System" be retained? THS......)
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Old 26th Feb 2017, 18:09
  #1365 (permalink)  
 
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Machinbird,

"From this, we see that development of the panic state is a two step process.
Activation of the Fight or Flight response
Inability to formulate/execute an effective evasive action."


I would disagree, in that it also takes two additional steps to activate the fight or flight response. Fight or flight does not initiate without two precursors that ennable the response. Fight or Flight is not a spontaneous condition, save for an individual who is predisposed to spontaneous panic? That is actually discussed in the DSM IV? Panic disorder.

"Stimuli"

1. Recognition. (stimulus)

2. Awareness (the conscious evaluation of the threat)

Which create the chemical flow that enables the conflict? (Fight or Flight)

The conflict then potentiates the panic, which flows from "unresolved anxiety/stress"

The state of panic can then prevent resolution, as the thought process degrades.

The PF had no opportunity to engage the only prevention of panic: "Assessment"? He had to move the controls, as we agreed to that earlier?
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Old 26th Feb 2017, 18:58
  #1366 (permalink)  
 
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IOW, what does "when stall protection became active" have to do with this initial, and ultimately unrecoverable Stall

You are correct, in that protections are lost in alternate law, so my remark was perhaps misleading and I should rephrase my comment to be "inhibited when stall warning became active".
If it had been so inhibited the THS would have been frozen at 3 deg NU. That would not have prevented the accident because the pilot's continued pitch up command would have resulted in the application of full up elevator which is quite enough to drive the aircraft into stall.
It would of course have made recovery easier, and incidentally would have prevented the aircraft from developing a 50 deg angle of attack so the position error would not have gone haywire, the indicated speed would not have dropped below 60 kts and the stall warning would not have been inhibited.

Others (pilots) will have to tell you if and why the pilot was at fault. I don't feel myself competent to comment on piloting affairs.

The THS "system" is retained because it is an integral part part of the basic C* system. The other systems you mention are self contained and separate.
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Old 26th Feb 2017, 19:58
  #1367 (permalink)  
 
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Originally Posted by Concours77
Fight or Flight is not a spontaneous condition,
Now I have personal experience that refutes that statement.
I went from normal alertness while flying formation to an adrenaline heart slam as I was looking to spot and avoid flaming wreckage (that fortunately did not materialize) when that other formation flew through our formation.

Is your source of information credible? Can you cite it? DSM-IV is not relevant since being crazy enough to fly jets is not a disorder.

Last edited by Machinbird; 26th Feb 2017 at 20:34. Reason: Note on DSM-IV
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Old 26th Feb 2017, 21:51
  #1368 (permalink)  
 
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THS

Hello. Owain Glyndwr

"It would of course have made recovery easier, and incidentally would have prevented the aircraft from developing a 50 deg angle of attack so the position error would not have gone haywire, the indicated speed would not have dropped below 60 kts and the stall warning would not have been inhibited."

The inhibited "StallStall" cricket created what might be argued as a "bar" to understanding that they were Stalled.

The Full Nose Up can not be defended, IMO, regardless the design consideration.

Did BEA do flight test to determine the extent to which the Taiilpane prevented or seriously inhibited recovery? If not BEA, then AI? The manufacturer has what is called a "duty of care". It is not to be glossed over... As With Concorde, we see a verdict that "apportions" responsibility, including jail?

I say again, the THS study is incomplete, and if the occasion to develop a rational foundation for safety sake was not addressed, more than incomplete, perhaps negligent.

Machinbird,

Quote:
"Originally Posted by Concours77
Fight or Flight is not a spontaneous condition,"

"Now I have personal experience that refutes that statement.
I went from normal alertness while flying formation to an adrenaline heart slam as I was looking to spot and avoid flaming wreckage (that fortunately did not materialize) when that other formation flew through our formation."

"Is your source of information credible? Can you cite it? DSM-IV is not relevant since being crazy enough to fly jets is not a disorder."

My source of information is credible. If you would like a cite, I can do that, otherwise I would ask you to trust that my statement is accurate.

I don't aim to be definitive here. I read, ponder and write quickly. What you read from me is a first draft, mistakes and all. I look to be corrected, that is a plus, an opportunity to learn from some one with more knowledge and experience...

I doubt what you call fight or flight happened spontaneously. The conflict itself is a product of sensation. Again, you cannot experience something you don't sense.

My proof would be my near miss over LA. I was piloting the Skylane, and my passenger grabbed my right arm. "Did you see that"? I said no. He said, "it was a twin, going "that way" he almost hit us!!"

I stayed calm, my immediate response was to check the instruments, reassure us both that we were straight and level, and that we experienced no contact.

My instinct was something to feel good about. I had no fear, no panic, no fight or flight....

I hadn't seen it. If I had, well, I like to think I would have told myself what I told myself in the moment. "We're OK, no contact, we're safe." The Skylane has no potty...but I checked later, any way...
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Old 26th Feb 2017, 22:07
  #1369 (permalink)  
 
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Sorry Concours, your example is not comparable. You didn't even see the threat.
No wonder you didn't get a fight or flight response. I saw the image of two planes (in the midst of my formation!) going from right to left. I had to then tell myself, "Its over, turn off the response," so that I could keep flying smooth formation.

Please cite your reference.
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Old 26th Feb 2017, 22:10
  #1370 (permalink)  
 
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My reference is my memory of a study in Psychology at the University. I remember the year, but I may have trouble locating the textbook....for now, will you agree that Fight or flight is a conscious and internal conflict?
My guess is you were well and truly startled, but your solution interrupted the more toxic binary dilemma?
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Old 26th Feb 2017, 22:12
  #1371 (permalink)  
 
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Auto-trim

In the midst of his discussion with Owain Glyndwr, Concours77 has quoted a paragraph I wrote in post #1359:
"The function of any auto-trim system is to remove the necessity for the PF or AP to continue to command the deflection of a primary flight control. In this case the auto-trim is concerned with pitch control, and adjusts the incidence (angle) of the THS (trim-able horizontal stabiliser) to enable the elevators to return to neutral in a few seconds after they have been deflected to comply with a command from the pilot or AP for a pitch-change (actually, in the case of C*, a change in normal G)."

That was a half-decent explanation of auto-trim, mainly for the benefit of pilots who haven't used it. But perhaps it can be improved in relation to Airbus FBW aeroplanes like the A330. It may also be helpful to reflect that auto-trim is merely an automated version of the various trimming systems with which virtually all aeroplanes have been fitted since the early days of aviation.

So here goes:
The function of a flight-control trimming system is to remove the necessity of a PF or AP to apply a continuing command to deflect a primary flight control in one direction. Pitch trim has been achieved traditionally by a hinged trim-tab which forms part of the trailing edge of an elevator. The pilot can adjust the position of the tab, which then exerts an aerodynamic force on the elevator as a substitute for the force previously exerted by the pilot's elevator control, which will then maintain the desired position "hands-off." Most large jet transports use a different system, in which changes of the angle of incidence of the "trimmable" horizontal stabiliser (THS) allow the elevators to return to neutral. On aircraft with conventional flight-control systems the elevators are controlled by the PF or the AP. In manual flight the PF uses a trim wheel or piccolo switches to move the THS, but with the AP engaged an auto-trim system moves it. In Airbus FBW with the AP disengaged the EFCS interprets the PF's sidestick position according to C* logic, which at cruise speed effectively means normal acceleration, and any resulting displacement of the elevators is reduced in due course by the auto-trim slowly moving the THS in the appropriate direction.

Please don't hesitate to inform me of any errors or possible improvements.
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Old 26th Feb 2017, 22:21
  #1372 (permalink)  
 
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Machinbird,

From the Harvard Medical School, paper on "the physiological reactions to stress" date not known.


"This combination of reactions to stress is also known as the "fight-or-flight" response because it evolved as a survival mechanism, enabling people and other mammals to react quickly to life-threatening situations. (The carefully orchestrated yet near-instantaneous sequence of hormonal changes and physiological responses helps someone to fight the threat off or flee to safety.) Unfortunately, the body can also overreact to stressors that are not life-threatening, such as traffic jams, work pressure, and family difficulties."

So my point is that fight or flight is a response triggering what I include in parenthesis, above.

Stimulus. A-4? "Conflict in flight path, bad, dangerous, or Jesus!!" A response, dependent on the stimulus, and the physiology of the result, the "conflict" I don't mean to parse words, but to say Flee or Fight is spontaneous ignores the physiology the body describes.
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Old 26th Feb 2017, 22:34
  #1373 (permalink)  
 
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Thanks Chris, it gets clearer and clearer....

My criticism remains in place though, since the elevators return to "neutral" and the THS has actually "supplanted" the elevators as primary flight control?

My concept of trim, even high altitude heavy jets, is that trim is a replacement for deflection, and is extremely suitable for Cruise. To the extent that aft loading of fuel helps fuel economy, it also challenges the stability of the airframe?

I fall back on the first lesson of trim, "not for maneuvering". But for tuning the attitude to allow continuous flight without constant correction, or deflection?

So I see the tailplane at -14 degrees as not a good idea when the purpose is to maneuver, to recover. At a time when Nose Down is a critical need, that immense aft "wing" is at its most powerful, and opposite to the appropriate input?

Imagine, "briskly Push the controls Nose Down, hold a descent, and carefully ascend when the risk of secondary Stall, is mitigated?"

I maintain the flight crew were cheated of that opportunity.... Perhaps a recovery was impossible, but I would quote the above post, where it is said "would have made recovery easier...."?
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Old 26th Feb 2017, 22:38
  #1374 (permalink)  
 
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I wasn't defending anything, merely trying to answer your question as to what effect THS inhibition might have had.
I should have known better than to offer facts to a lawyer - a mistake I won't make again
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Old 26th Feb 2017, 22:46
  #1375 (permalink)  
 
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Well

I admit to a fear response when I see you have responded....

No, I take everything you say as Gospel. My comment is an opinion, and I did not sense that you were defending a position. Your position needs no defense.
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Old 27th Feb 2017, 00:09
  #1376 (permalink)  
 
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Quotes from Concours77:
(1) "... the elevators return to "neutral" and the THS has actually "supplanted" the elevators as primary flight control?"

No, the THS remains the secondary flight control, having merely backed-up the activity of the elevators, which remain always the primary. If at any time the PF gives consistent inputs in the reverse sense, the THS will in due course travel in the appropriate, opposite direction. The auto-trim has no bias in one direction or the other, and it is certainly not a ratchet-type device.

(2) "I fall back on the first lesson of trim, "not for maneuvering". But for tuning the attitude to allow continuous flight without constant correction, or deflection?"

The first lesson of trim is ALWAYS to use the primary control first, and then unload the primary control with trim. Never use trim as the primary control, except (once in many lifetimes) when the primary control fails.

(3) "To the extent that aft loading of fuel helps fuel economy, it also challenges the stability of the airframe?"

No. Life is a compromise in regard to safety and stability, or we would never get out of bed. And so is aircraft stability.

(4) "Imagine, "briskly Push the controls Nose Down, hold a descent, and carefully ascend when the risk of secondary Stall, is mitigated?"
I maintain the flight crew were cheated of that opportunity...."


First of all, as far as we know the two co-pilots never recognised that the aircraft was stalled, which is what Machinbird's hypothesis is investigating. AFAIK they never attempted a stall recovery.

Had they attempted a stall recovery, would they have been cheated of it? IIRC, Owain has previously calculated that, even with the THS at full nose-up (NU) trim, there is enough elevator authority to pitch the A330 down. And there is evidence that the A330, height permitting, is recoverable from extreme alphas as in AF447. But it's true that the rate of pitch-down would be lower with full NU than a lower angle.

Setting that aside, there comes a point in any control-departure when an aircraft cannot be recovered before impact. This crew took the aircraft to that point, and then well beyond it. They seem to have misdiagnosed an overspeed when it should have been evident that the (presumably unintended) rapid climb of no less than 2000 ft would have depleted the vast majority of the aircraft's kinetic energy.
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Old 27th Feb 2017, 02:30
  #1377 (permalink)  
 
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carefully orchestrated yet near-instantaneous sequence of hormonal changes and physiological responses
Concours
There is a triggering sequence for activation of fight or flight, but as your own reference indicates, it is near instantaneous, at least within the body's own internal measurement of time. Once triggered by visual, audio, or by physical impact, activation of the fight or flight response moves at nerve impulse velocity to prepare the body for action.

The BEA in their final recommendations noted the effect of "Startlement" as the cause of the accident. If you substitute triggering the fight or flight response for "startlement" you come pretty close to my own assessment of fight or flight response triggering and leading to panic when the roll became unstable.

Originally Posted by BEA FINAL REPORT AF447-CONCLUSIONS
The startle effect played a major role in the destabilisation of the flight path and
in the two pilots understanding the situation. Initial and recurrent training as
delivered today do not promote and test the capacity to react to the unexpected.
Indeed the exercises are repetitive, well known to crews and do not enable skills in
resource management to be tested outside of this context. All of the effort invested
in anticipation and predetermination of procedural responses does not exclude the
possibility of situations with a “fundamental surprise“ for which the current system
does not generate the indispensable capacity to react.
The rapid increase in crew workload in an unusual and unexpected situation led to the
degradation of the quality of communication and coordination between the pilots.

Last edited by Machinbird; 27th Feb 2017 at 03:28. Reason: double word
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Old 27th Feb 2017, 03:25
  #1378 (permalink)  
 
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Chris,
That is a good summary of the trim function. It was surprising how stable AF447 was in the stall. I initially expected that such an aircraft would drop a wing and progress into a spin, but that did not happen. I have to attribute that to the automatic action of the yaw damper.

In Normal Law THS trim is limited by AOA protection activation.
From FCOM
When angle of attack protection is active, THS is limited between setting at entry in
protection and 2 nose down (i.e. further nose up trim cannot be applied).
For some reason, in Alternate Law, there is no inhibition on nose up trim related to angle of attack. It would seem logical to inhibit THS trim at stall warning activation when in Alternate Law. From Owain's comments recovery from stall would have been greatly enhanced.
Originally Posted by Owain
If it had been so inhibited the THS would have been frozen at 3 deg NU. That would not have prevented the accident because the pilot's continued pitch up command would have resulted in the application of full up elevator which is quite enough to drive the aircraft into stall.
It would of course have made recovery easier, and incidentally would have prevented the aircraft from developing a 50 deg angle of attack so the position error would not have gone haywire, the indicated speed would not have dropped below 60 kts and the stall warning would not have been inhibited.
The BEA did not address the lack of THS trim limits in Alternate law in the accident recommendations. I have to assume that there were good engineering reasons for not adopting limits on the THS trim system in Alternate law, but I have no clue what they might be.
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Old 27th Feb 2017, 09:49
  #1379 (permalink)  
 
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A question? I asked Owain Glyndwr at one point why the graph in the report of the THS movement looks "smooth"? Yet the graph of the stick trace looks anything but? The trace is full of bumps, up and down....
The traces released by the BEA from the 'readout' of the DFDR on AF447 were rather coarse in comparison to those released from other crash investigations.
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Old 27th Feb 2017, 11:47
  #1380 (permalink)  
 
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Quote from Concours77 [my emphasis]:
"I asked Owain Glyndwr at one point why the graph in the report of the THS movement looks "smooth"? Yet the graph of the stick trace looks anything but? The trace is full of bumps, up and down...."

Here is a video of an A320 co-pilot handling the sidestick on what is probably a fairly average day:

https://www.youtube.com/watch?v=vBuoA9qkKi4

(Several other similar videos are available on line.) The aircraft is presumably in Normal Law, but the pilot is consistently over-controlling the sidestick; behaviour that I often saw from the jump seat during many years of line-checking on the A320. I doubt that the pilot concerned was even aware he was doing it.

In AF447, the control laws were C* in pitch, but Direct in roll. That makes for a bad combination, because a lot of firm** movements may have to be made to keep the wings level, while only small movements are appropriate in pitch. With the Airbus sidestick it is more difficult to avoid roll commands affecting pitch commands (and vice-versa) than it is on the traditional column/control-wheel combination.

** [EDIT, in deference to comment by IcePack - below]:
(larger than those needed for pitch)

Last edited by Chris Scott; 27th Feb 2017 at 17:00. Reason: See **
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