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AF 447 Thread No. 10

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AF 447 Thread No. 10

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Old 20th Aug 2012, 23:11
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AF 447 Thread No. 10

Thread part -

(a) #1 starts here and finishes here. Posts = 3895
(b) #2 starts here and finishes here. Posts = 2537
(c) #3 starts here and finishes here. Posts = 2073
(d) #4 starts here and finishes here. Posts = 1070
(e) #5 starts here and finishes here. Posts = 1980
(f) #6 starts here and finishes here. Posts = 1696
(g) #7 starts here and finishes here. Posts = 1355
(h) #8 starts here and finishes here. Posts = 1552
(i) #9 starts here and finishes here. Posts = 1476

Total posts to date = 17634 .. with in excess of 2.7 million views overall.


Links to the various BEA reports are given below. If I have missed any of the useful papers, please PM me with the URL and I can include it.

(a) BEA site - French, English
- Report link page - French, English

(b) Interim Report (No, 1) Jul 2, 2009 - English

(c) Interim Report No. 2 Dec 17, 2009 - English
- Update Dec 17, 2009 - French, English

(d) Estimating the wreckage location Jun 30, 2010

(e) Wreckage search analysis Jan 20, 2011

(f) Briefing and associated update May 27, 2011
- Briefing - update French
- Briefing - update English
- Briefing - update German
- Briefing - update Portugese

(g) Interim Report No. 3 July 2011 - French, English

(h) Links to final report Jul 5, 2012 and associated documents.

Miscellaneous pertinent links -

(a) Airbus Operations Golden Rules
(b) ALPA FBW Primer
(c) C* and Civil Transports - Cranfield
(d) Longitudinal Flight Control Design - RAeS
(e) Longitudinal Stability: Effect of High Altitude and CG - Boeing
(f) pitot static system performance - USN (Pax River) FTM
(g) The Problem of Automation: Inappropriate Feedback and Interaction, Not Over-Automation. Donald A. Norman UCSD
(h) Upset Recovery - 16MB zip file
(i) Ironies of Automation. Lisanne Bainbridge UCL
(j) Cognitive Capability of Humans. Christopher Wickens Uni Illinois
(k) Trust in Automation: Designing for Appropriate Reliance John D. Lee, Katrina A. See; Human Factors, Vol. 46, 2004
(l) Training for New Technology. John Bent - Cathay Neil Krey's CRM site


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Old 21st Aug 2012, 00:57
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Originally Posted by Lyman

Has it at any time been attempted to hold the trim wheel to prevent Autotrim?
Have line pilots ever done this? In addition to quick sticking to prevent the THS from Trimming? Could something have gotten stuck in one of the wheels? Was anyone sitting or resting a foot on the pedestal?
In the narrowbodies, I've attempted manual trim as per the FCOM' statement that manual trim is available and primary at all times. The manual lies. Auto trim fights the man trim wheel and removes any pilot applied man trim as soon as the pilot releases the wheel. When forced, the trim wheel will make jerk-y pitch movements.

In NO sense, does Airbus manual trim resemble manual trim in any other civilian jet of my experience. (various models of Lear, B737-engineering sim, DC9)

It is highly unlikely that anything could jam/interfere with the manual trim wheels. Only the top quarter of the wheel is available and it's tightly "cowled".

Last edited by TTex600; 21st Aug 2012 at 00:58.
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Old 21st Aug 2012, 02:49
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Originally Posted by TTex600
In the narrowbodies, I've attempted manual trim as per the FCOM' statement that manual trim is available and primary at all times. The manual lies. Auto trim fights the man trim wheel and removes any pilot applied man trim as soon as the pilot releases the wheel. When forced, the trim wheel will make jerk-y pitch movements.
Not really a surprising result. In Normal and Alternate 1&2 Laws, holding the trim wheel can result in inadequate control effectiveness for proper operation of the flight control system.

Of course, if the flight control system is off in La La land, you still can seize control, but it will be at the expense of someones free hand and (apparently) smooth control. If you do this, you are fully responsible for observing all aircraft limits, so I can understand a bit of caution in applying this technique, but ultimately you do have the "hammer" should you want to use it. The crew of AF447 could have stopped the trim from its run to the nose up trim limits if they had been aware of the motion.

Just as there isn't any good reason to point the nose high in the air at cruise altitude, there is also no good reason to have full nose up trim dialed in at cruise altitudes.
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Old 21st Aug 2012, 04:06
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Disturbing post

Good grief, Tex.

Your war story scares the hell outta me.

For some reason, I expect that when the human "commands" something, that the machine will obey.

Sheesh, I can see HAL learning how to read lips in order to counter the clever humans.
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Old 21st Aug 2012, 07:23
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Machinbird;

The BEA Final Report into the XL Airways A320 accident at Perpignan makes for interesting reading, bearing in mind what information has been provided thus far on the THS design, stall warnings, normal, alternate and direct laws and so on. (The G-THOF incident has been brought up here before).

We know that the THS is the long term follow-up to elevator input and so with AF447 and here the trim dutifully followed the sidestick commands as the stall exercise at Perpignan was approached. Some here have offered the notion that the THS should stop trimming at some point but what are the all the effects of such a design change? Should it be stopped at a stall indication? In these two accidents that would have been too late as the THS was already at the NU stop. Ironically, for AF447, stopping the autotrim function at that point would remove the ability of the autotrim to follow a ND stick order and reduce from -13.6 back to normal as the trim did in our little sim exercise, as it would have for AF447. However, for the XL A320 dropped from normal to alternate and then quickly to direct law where manual trim was required but by that time things were happening too fast. There's an animation on the BEA site, (with a caution not to use it to come to specific conclusions...a caution for ALL animations!)

TTex600, re the autotrim and THS, you told only part of the story! The trim went back to its original setting when you fiddled with it because that's what it is and does...it's a full-time autotrim in normal and alternate laws. Manual (mechanical) trim IS available at all times just as the FCOM says, when needed, (such as in direct law or a G+Y Hyd flr), it will stay in the position the pilot puts it in. That's just part of knowing one's airplane. Hey gums...no worries.


From the BEA Report, p.92-93:

2.4 Functioning of the Automated Systems

When the real angle of attack increased, the blockage of AOA sensors 1 and 2 at similar values caused the rejection of the ADR 3 anemometric values, even though these were valid. This rejection was performed by vote without any check that the parameters were consistent with each other. The crew was not aware of this rejection, except indirectly through the loss of CAT 3 DUAL approach capacity.

The low values of the limit speeds did not attract the crew’s attention. Due to the blockage of the AOA sensors, calculation of the limit speeds was erroneous and the triggering of the AOA protections in normal law was rendered impossible. The values of the speeds corresponding to angle of attack protections (Vaprot and Vamax) were proportional to the computed airspeed of the aeroplane (see 1.16.2). The display of the amber CHECK GW message on the MCDU(58), a consequence of the gap between weights calculated on the one hand by the FAC, based on the angle of attack, and on the other hand by the FMS, based on the takeoff weight and the fuel consumption, would have allowed this anomaly to be detected. This message is however associated with no aural warning, which contributes to reducing its importance.

On approach to stall and taking into account the dynamic of the flight and of the complexity of the displays, the automatic changes in the control laws can fail to be perceived and their consequences can sometimes be misunderstood by pilots. In this case, the passage to direct law rendered the auto-trim function inoperative. Even if the amber USE MAN PITCH TRIM flag was displayed on the two PFD artificial horizons, the crew did not notice the position of the stabilizer and did not command the trim wheel manually during the twentyfive seconds in direct law between 15 h 45 min 15 s and 15 h 45 min 40 s. From this time on and for the rest off the flight, as a result of passing into abnormal attitudes law, the amber USE MAN PITCH TRIM flag was no longer displayed. The systems thus functioned in a degraded manner, without the real overall situation of the aeroplane being known by the crew.

The necessity to trim the aeroplane manually can occur in a situation that is already degraded, as was the case during the accident. This then leaves the crew no time to analyze the situation, especially since, on this type of aeroplane, the crew was used to not performing this task in normal operations. One of the only circumstances in which a pilot can be confronted with the manual utilisation of the trim wheel is during simulator training. However, in this case, the exercises generally start in stabilized situations. It should also be noted that the technique for approach to stall does not remind crews of the possible need to have recourse to the trim wheel in direct law. This absence de reference to the use of the trim is also mentioned in AAIB report into a serious incident to a Boeing 737 on 23 September 2007(59). In addition, the angle of attack constitutes essential information to characterize the situation of an aeroplane on approach to stall, while the speed information is that which is always used.

(59) http://www.aaib.
gov.uk/publications/
bulletins/june_2009/
summary___
aar_3_2009___
boeing_737_3q8__g_
thof.cfm

Last edited by PJ2; 21st Aug 2012 at 07:29.
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Old 21st Aug 2012, 10:04
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Originally Posted by PJ2
Some here have offered the notion that the THS should stop trimming at some point but what are the all the effects of such a design change? Should it be stopped at a stall indication? In these two accidents that would have been too late as the THS was already at the NU stop.
I agree that inhibiting autotrim would not be a good idea. But how about limiting the range of THS settings it trims to as suggested in my post here? That would retain autotrim for trimming nose-down in response to sidestick demand, just as it does in normal law above alpha-prot.

EDIT:: In AF447 the THS was at about 3.1 degrees NU at stall warning 2. The effect of limiting the THS to that value is described here.

Last edited by HazelNuts39; 21st Aug 2012 at 11:55. Reason: wording change
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Old 21st Aug 2012, 12:26
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Originally Posted by PJ2 View Post
Some here have offered the notion that the THS should stop trimming at some point but what are the all the effects of such a design change? Should it be stopped at a stall indication? In these two accidents that would have been too late as the THS was already at the NU stop. Ironically, for AF447, stopping the autotrim function at that point would remove the ability of the autotrim to follow a ND stick order and reduce from -13.6 back to normal as the trim did in our little sim exercise, as it would have for AF447.
Mhmm, are you sure?
I agree for Perpignan's A320, but not for AF447: In the latter case, the trim was -3° when the stall warning went on, and the motion toward -13° was done with the stall warning shouting all the long.

Still, as stated previously, I'm no more advocating that inhibiting the NU autotrim when S/W in ON would be such a good idea:
1/ Someone quoted the "black swan" theory, and that's worth to think about (plus the fact that under the current implementation, the elevators may try to compensate for the "unavailability" of the autotrim).
2/ As you said, that would be of no use at all in a Perpignan-like scenario.

KISS principle. If autotrim available ("normal" scenario, the crew must be aware of that, and of how it works). If autotrim not available, the crew must be notified of that (USE MAN PITCH TRIM must be displayed, which was not always the case in the system logic, IIRC that has to be (has been?) corrected).

Last edited by AlphaZuluRomeo; 21st Aug 2012 at 12:32.
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Old 21st Aug 2012, 13:15
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Originally Posted by PJ2
TTex600, re the autotrim and THS, you told only part of the story! The trim went back to its original setting when you fiddled with it because that's what it is and does...it's a full-time autotrim in normal and alternate laws. Manual (mechanical) trim IS available at all times just as the FCOM says, when needed, (such as in direct law or a G+Y Hyd flr), it will stay in the position the pilot puts it in. That's just part of knowing one's airplane.
PJ2, I told the story the books tell. My original, literal, reading of the manual said that man trim always works. The books mean what you write, but in today's "self study" world such language should be more clear. Truth is, it is only usable, it only works when the computers give up and say use man trim.

As usual, my round-a-bout point is that the bus doesn't fly like "any other airplane". I have attempted to "fly it like any other airplane"' and it DONT. Some have a seeming desire to discus this accident as if the Bus is flown like the airplane they retired from, or like an airplane that is pilot flown vs computer flown; some want to assume that Bus trim works from their perspective. This just isn't so. One needs to place one's self in Bonin/Roberts exact shoes before judgement.

Edit to add: the bus almost totally removes trim from the pilots conscience thought process. More later

Last edited by TTex600; 21st Aug 2012 at 14:27. Reason: Spelling
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Old 21st Aug 2012, 15:55
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...autotrim to follow a ND stick order and reduce from -13.6 back to normal as the trim did in our little sim exercise, as it would have for AF447.
I have observed both the autotrim response you describe and the response that CONF described in his exercise. I think there may be more to this.

...but in today's "self study" world such language should be more clear
I always felt the best instructional aid was an expert with a piece of chalk in his hand.

Whatever happened to chalk.....or for that matter, experts?
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Old 21st Aug 2012, 18:46
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Originally Posted by TTex600 View Post
Auto trim fights the man trim wheel and removes any pilot applied man trim as soon as the pilot releases the wheel. When forced, the trim wheel will make jerk-y pitch movements.

In NO sense, does Airbus manual trim resemble manual trim in any other civilian jet of my experience. (various models of Lear, B737-engineering sim, DC9)
Hey Tex. Autotrim won't "fight" the manual trim wheel, but you will probably feel the electro-mechanical interlocks disengage when you hold it for the first time. As PJ2 says, when in Normal and Alternate laws, letting go of the manual trim wheel will allow autotrim to re-engage - this is per design. If you want to keep the trim held where it is you will have to hold the wheel in position - you may even get a warning that autotrim has been inhibited, but as this is what you're presumably trying to do this shouldn't be a surprise.

Originally Posted by TTex600 View Post
As usual, my round-a-bout point is that the bus doesn't fly like "any other airplane". I have attempted to "fly it like any other airplane"' and it DONT.
I think your interpretation is too literal - but that's fair enough, given that the statement "like any other aircraft" isn't especially clear. That statement is usually made to counter the misapprehension that the FBW bus is under automatic control at all times and cannot be hand-flown. It can of course be hand-flown, and the pitch, bank and yaw commands are essentially performed in the same manner as any other aircraft through the PFC and rudder pedals.

The trim arrangement is not the same - by design - but the average layman is unlikely to know what trim does, and so that's usually put aside. The FBW Airbus pilot is not required to have trim as part of their conscious thought process, and the fact that autotrim has barely warranted discussion up until now implies that in almost all cases, that's not a problem because the system is very reliable.

In this particular design, manual trim has gone the way of wing-warping, trim tabs and cable reversion - in that other ways to implement that function have been found that either reduce pilot workload or design complexity. A pilot that does not have to trim manually is no less a pilot for not having to do so, and just because older types required manual trim to be part of the pilots' muscle memory does not mean that it should always be so.

The fundamental fact is that the trim worked the way it did because the PF's pitch commands required it to. Maybe it's worth revisiting that behaviour, maybe it isn't - but to make a blanket design change that would involve significant man hours in development, fitting and re-training on the basis of one relatively minor factor in one accident - a factor that was a consequence of crew action - would be foolish.
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Old 21st Aug 2012, 19:14
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Hey Tex. Autotrim won't "fight" the manual trim wheel, but you will probably feel the electro-mechanical interlocks disengage when you hold it for the first time.
And you'll feel them again & again & again &......as you continue to hold the trim wheel and it 'fights' you.
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Old 21st Aug 2012, 19:18
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If I understand the design, it'll disengage as soon as it feels any resistance - so it won't try to move the wheel against the direction it's being moved in or against the position at which it's being held. In that sense it's checking to see if it can re-engage, but it won't actively counter (i.e. "fight") what the pilot is doing with it.

Last edited by DozyWannabe; 21st Aug 2012 at 19:19.
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Old 21st Aug 2012, 19:24
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...so it won't try to move the wheel against the direction it's being moved in or against the position at which it's being held.
It would appear that 'checking' is done by 're-engaging' as indicated on the SD FLT CTL page by momentary movements of about .2-.3.
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Old 21st Aug 2012, 19:37
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Devil

Originally Posted by DW
one relatively minor factor in one accident
... etc.

DW, in this 10. thread you work as designed.

Two different conceptions of effective aircrafts
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Old 21st Aug 2012, 19:42
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@roulishollandais:

The systems status of AF447 and Perpignan was different, so I'm treating them as unrelated until strong evidence suggests otherwise.

The "Effective Aircraft" theory seems to be yours alone, and I must confess I don't follow it, but that's possibly because I'm a poor reader.

Last edited by DozyWannabe; 21st Aug 2012 at 19:43.
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Old 21st Aug 2012, 20:22
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Snoop

1. "Effective aircraft"
Originally Posted by Dozy Wannabe
The "Effective Aircraft" theory seems to be yours alone, and I must confess I don't follow it, but that's possibly because I'm a poor reader
Aviation safety and pilot control: understanding and preventing unfavorable Pilot-Vehicle Interactions
isbn=0309056888...National Research Council (U.S.). Committee on the Effects of Aircraft-Pilot Coupling on Flight Safety - 1997 - Transportation - 208 pages
Implications for Design of the Effective Aircraft Dynamics Reduce time lags in the high-frequency effective aircraft dynamics. To reduce tendencies for ...

In this book (1997), some very good Machinbird reference, you will find 51 occurences of "effective aircraft".
[/quote]

I already posted this reference months ago...
I would have been very proud to have the idea of that perfect concept !

2.
Originally Posted by Dozy Wannabe
one relatively minor factor in one accident
I did not compare AF447 and Perpignan flights, every crash is a new one and always something different, but your philosophy of design based on insurance rates vs trying to progress in air safety, improving the methods.
One crash is not less serious than ten, if working better in system conception would help to decrease that number, and we refuse to do it. Research and development is mandatory.

Last edited by Jetdriver; 22nd Aug 2012 at 00:43.
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Old 21st Aug 2012, 21:18
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OK - so looking at that document, I notice two things.
  1. The document itself seems to be a treatise on Aircraft-Pilot Coupling, with a focus on Pilot-Induced Oscillation.
  2. The term "effective aircraft" seems to be used in the "existing in fact; not theoretical; real;" sense, not the "able to accomplish a purpose; functioning effectively;" sense.

The FBW Airbii seem to be no more susceptible to PIO/APC than any other type based on the amount of time they've been around and no discrepancy has shown itself, and the fact that there is no significant positive discrepancy in accidents between FBW Airbii and other types suggests that Airbus's "effective aircraft" design is no more or less flawed than any other modern type.

Last edited by DozyWannabe; 21st Aug 2012 at 21:37.
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Old 22nd Aug 2012, 07:31
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Semantics: The theory seems to be about "Effective Aircraft Dynamics", i.e. the dynamics of aircraft, effectively, or the effective dynamics of aircraft (and pilot).

Last edited by HazelNuts39; 22nd Aug 2012 at 08:53.
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Old 22nd Aug 2012, 08:02
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HN39, re
Originally Posted by post #6 [URL
http://www.pprune.org/tech-log/493472-af-447-thread-no-10-a.html#post7370832]I[/URL] agree that inhibiting autotrim would not be a good idea. But how about limiting the range of THS settings it trims to as suggested in my post here? That would retain autotrim for trimming nose-down in response to sidestick demand, just as it does in normal law above alpha-prot. EDIT:: InAF447 the THS was at about 3.1 degrees NU at stall warning 2. The effect of limiting the THS to that value is described here.
HN39, AZR, first, thank you for your responses and links and for your reminder re the trim value at stall warning 2 for AF447.

As the discussion had turned to autotrim, elevator and their behaviours I was curious to see if the Perpignan accident which was an intentional reduction of speed to test low-speed flight and the alpha response, offered any new understanding.

As expected the THS moved to trim NU as the stick was held back and speed reduced. The flight data shows that the THS reached the NU limit at the same time that the stall warning occurred, (I still don't know if a stall warning stops the autotrim on the A320 or not. I suspect not). Accordingto the BEA Report, stick inputs at the initial stall were insufficient to cause the THS setting to move ND. The aircraft reacted to the developing stall and rolled, with sideslip causing a disparity between the airspeeds ADRs 1 & 2. This caused the FAC then ELAC to reject all three ADRs and the flight control laws reverted to direct law, requiring manual input to the THS which was annunciated on the two PFDs.

This is a case in which the THS would not have moved towards the NU position with forward stick if autotrim were stopped with the stall warning.

The case may be "academic" in some eyes due to the fact that there was no time for forward stick but it serves as a sufficient counter-example to indicate that the idea needs careful thought. If Bonin had placed the stick full-forward and held it, we know that there was a likely chance for recovery. But there is a great deal behind any such pilot's decision to take such action.

So AZR I agree with you regarding not stopping the autotrim at a stall warning and I'm merely adding here something to the recent discussions on THS and elevator behaviours which I think hasn't been considered, (unless I've missed someone else's comment on this).

I agree with you HN39 regarding limiting the autotrim in some form. My thought is, as the Perpignan accident serves to illustrate, at what point and for what reason should the autotrim be stopped in its motion (either way), and then re-engaged again?

It IS re-engaged in one circumstance: The abnormal attitudes law, in which autotrim is stopped but re-engaged once the abnormal attitude limits are no longer exceeded and the aircraft is recovered, (AMM).

TTex600; Re
One needs to place one's self in Bonin/Roberts exact shoes before judgement.
I don't think anyone who knows this business is "judging" this crew. Judging means one believes it can't happen to them and most of us know better. Many have said, "There but for the grace of god, etc"but in a way that isn't the case either because thirty-odd other crews WERE in Bonin's and Roberts' shoes and nothing untoward occurred. Why?

This is a performance accident. There is nothing about the airplane that caused an absence of SOPs, CRM, a disciplined cockpit and a disagreement between crew members which went unaddressed and unresolved, (PM taking control, PF taking it back after PM says get the nose down, etc). This absence has been noted by the BEA and much earlier by many here including me. That isn't judging the crew, that is asking why, when SOPs, CRM etc are what we do, they didn't respond as expected of an airline transport crew. Training, checking, standards, a professional culture are intended to ensure the performance of these fundamental and critical tasks but here that did not occur. Why? Startle effect has been noted for many years now. No one is immune of course, but the difference in the character of response is what solid training, knowledge, memory items and disciplined CRM is about. For lack of a better word, a "fear" has crept into the checking and standards regimes partly due to risks of liability but also through other, more subtle reasons, that prevents some required bluntness and otherwise clear address regarding crew performances. I would never return to some of the means I've seen to "ensure" crews do their job but the cockpit isn't a democracy, either.

If the airplane let them down, even in part and after they were well into serious trouble, then we need to ask the question, would another random crew similarly be "let down"? If so, how, when and why?

Last edited by PJ2; 22nd Aug 2012 at 08:14.
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Old 22nd Aug 2012, 09:11
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Startle effect ?
I think these pilots indeed had enough reasons to be suffering from startle effect
However, the result was different from that of AF447
Why?
The answer is not difficult to find

United Airlines Flight 232 - Wikipedia, the free encyclopedia
So ... fail to prepare .... prepare to fail

Last edited by jcjeant; 22nd Aug 2012 at 09:15.
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