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AF447 final crew conversation - Thread No. 1

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AF447 final crew conversation - Thread No. 1

Old 12th Dec 2011, 08:36
  #741 (permalink)  
 
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An extract from the PM article posted some time ago .....

At 1h51m, the cockpit becomes illuminated by a strange electrical phenomenon. The co-pilot in the right-hand seat, an inexperienced 32-year-old named Pierre-Cédric Bonin, asks, "What's that?" The captain, Marc Dubois, a veteran with more than 11,000 hours of flight time, tells him it is St. Elmo's fire, a phenomenon often found with thunderstorms at these latitudes.
Amazing Bonin question about St Elmo fire
In any case from a commercial pilot
No need to have a university education or be a veteran pilot to know what is a St Helmo fire
I wonder more and more questions about the knowledge of Mr Bonin
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Old 12th Dec 2011, 10:37
  #742 (permalink)  
 
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" Amazing Bonin question about St Elmo fire ".....
Agreed! This is something I learned about in my instrument ground school and SAW during my instrument flight training. To me, this tragedy is very much related to TRAINING.....or lack thereof.....I guess I was just 'lucky' to have a very good primary, instrument, multi and commercial instructor. I know that training is a 'cost'....but where do we draw the line between 'cost' and SAFETY? Or....DO WE??
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Old 12th Dec 2011, 13:16
  #743 (permalink)  
 
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Had they had 'conventional' controls, F/O Bonins' full nose up control input would have been a thousand times more obvious as he would have been hauling back on the yoke and probably with both hands.
can someone tell me (an interested slf) how it works with boeing´s 777 and 787 which are fbw as well but have no sidesticks? do both the yokes move the same? can one pilot feel the "force" performed by the other pilot?
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Old 12th Dec 2011, 14:40
  #744 (permalink)  
 
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(slightly simplified, but along the general layout)


On the modern Boeings the two yokes are interconnected, thus move the same way. Force felt on one side is according to input force from the other. It is done by a so called drive back. This is a artificial replication of the force input to the ACEs (actuator control electronics) by the pilots.
The ACEs transmit the input to the PFCs (primary flight computers) who then process it and send it back to the ACEs who in turn actuate the hydraulics for the flight control surfaces.
If the input sensed by the PFCs exceeds the programmed parameters of the envelope or protection, the PFCs increase the necessary force up to not executing the commands. However, if the pilot then increases his own input force above a certain value, the PFCs give up and say: "You want it, you get it" and the input is routed directly to the ACEs for execution.

This latter function is the so called soft protection, as opposed to the hard protection of the Airbus that does not allow override of the protections. Only if 3 of the 5 Airbus computers (2 Prims and 1 Sec) are switched off from the overhead panel, the system goes into direct law and then allows unprocessed input.
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Old 12th Dec 2011, 15:08
  #745 (permalink)  
 
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sf25 - can someone tell me (an interested slf) how it works with boeing´s 777 and 787 which are fbw as well but have no sidesticks? do both the yokes move the same? can one pilot feel the "force" performed by the other pilot?


777 works like every other airplane. The yokes move together. It is visually obvious what inputs the flying pilot is doing.
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Old 12th Dec 2011, 15:24
  #746 (permalink)  
 
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Shy talk, - “The issue with the sidestick is important.”
Not necessarily as you infer. An aircraft’s response to control input is the combined effects of stick and trim, with the latter providing a significant, perhaps dominant effect. You can compare this with previous accidents / incidents where conventional aircraft suffered upsets due to incorrect trim position; there are several involving go around.

A difference between conventional and sidestick is the trim force. With conventional aircraft an out of trim situation might be detected by an abnormal force, and many pilots take this as an indication of the aircraft position / motion, which is not always true – a lazy, inferred assessment of the control situation.
With a side stick (without feedback), there is no trim force, thus an alternative method of checking trim state is required – look at the trim wheel, check trim indications.

This is not an issue of one system being better than another, it’s that they are different, but the industry has grown up with a force system and this provides a general understanding of the norm.
In normal and those abnormal situations which had been considered, the sidestick system is quite adequate and may have safety and workload advantages.
With AF447 the particular situation was apparently unforeseen, the trim functioned as designed, but together with the surprise and complexity of overall situation the crew had difficulty in determining the situation.
The situation was novel; it required time, knowledge, and reasoned assessment (and reassessment). It appears that these aspects either ran out or did not occur.

Re coupled sticks; it could be incorrect to accept that stick position, coupled or not represents what the aircraft is doing. Checking, monitoring, and establishing the true situation requires looking at the output of control systems – what the aircraft is actually doing.
This requires assessment of the flight instruments, some of which were not available / accurate in AF447.
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Old 12th Dec 2011, 15:49
  #747 (permalink)  
 
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About the sidesticks. It is my understanding that Airbus sidestick inputs are taken as requested deviations in control surface positions, and not as states for these positions. That is, when a pilot wants to adjust the attitude of the plane by some finite amount, s/he pulls the SS back/forward a specified amount, AND THEN RELEASES THE SS which then returns to a neutral position. The amount of the initial deflection in the SS is what determines the degree of attitude change. Holding the SS at a deflected position causes continually cumulative control surface inputs in that direction.

Thus, isn't it extraordinary that Bonin kept the SS in a deflected back position? Or is my understanding of how the SS works incorrect?
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Old 12th Dec 2011, 15:58
  #748 (permalink)  

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"This requires assessment of the flight instruments, some of which were not available / accurate in AF447"

As I understand it, at least the standby AI (if not the main AI) was functional.

I would have thought that the sight of a lot of blue might have been a hint that they had a rather excessive NU attitude and that consequently their rapid descent might indicate a stall.

Admittedly the main AI may have been almost obscured by alarm messages but from what I have read the standby AI was working.

But what do I know......?
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Old 12th Dec 2011, 18:25
  #749 (permalink)  
 
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With more tragic irony than flippancy, I propose a slight redesign of the AB sidesticks: a bamboo stick 12-18" long, tied onto each side with two rubber bands.

And that Airline subsidise and mandate glider and/or microlight hours, say 20/year.

My CTSW will do the pilot held stall thingy, showing 28kts IAS or less on high power, plus a dollop of neg VSI
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Old 12th Dec 2011, 18:49
  #750 (permalink)  
 
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SeenItAll

Excellent points, but a hard sell, at least here. It is not in the interest of the fanatics to accept exculpatory reasoning (exonerating). The PF did not achieve PITCH plus actual for ten seconds (per BEA: "The aircraft did not immediately climb"). We are all also unaware of what the PF saw on his Panel.

PEI_3721

You do not address the point. This is not about TRIM, nor is it in re: feedback, or anything else. This discussion is about "POSITION" of the stick, and its importance to the PM. Had PNF SEEN THE STICK FULL BACK, he would have sussed the problem........period.
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Old 12th Dec 2011, 19:42
  #751 (permalink)  
 
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Well again; beating a dead horse; with conventional control columns/wheels, there wouldn't be an accident investigation about AF447.
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Old 12th Dec 2011, 19:49
  #752 (permalink)  
 
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SeenItAll,

Your understanding is not correct.
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Old 12th Dec 2011, 20:10
  #753 (permalink)  
 
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Lyman (#757), agreed, it’s not all about trim, it’s about force, but that comes via trim in conventional aircraft.
Thence please read my last para (#753):
Re coupled sticks; it could be incorrect to accept that stick position, coupled or not represents what the aircraft is doing. Checking, monitoring, and establishing the true situation requires looking at the output of control systems – what the aircraft is actually doing.

Do you mean that with coupled sticks, and both full back, this would indicate the aircraft flight path – which with AF447 was actually descending?
There have been accidents and incidents where a nose-up mis-trim and full forward stick resulted in a nose-up attitude and climb; the significant difference with AF447 is the aerodynamics, one condition was not stalled, the other was.
Pilots have to assess the situation, determine the aerodynamic state of the aircraft and then act accordingly. Control stick input position does not indicate aerodynamic state, although within suitable confines of trim position it will determine an aerodynamic state.

Re your loud “Had PNF SEEN THE STICK FULL BACK, he would have sussed the problem........period.
Then, you will have to explain why any other pilot might have questioned why the aircraft was not climbing with the stick full back. This might have been the dilemma which AF447 crew were pondering, to the point of distraction.
The aircraft was descending, the stick was back, but the descent was not arrested. Unfortunately, between the ‘up’ and the subsequent ‘down’, the aerodynamic sate changed (stall), the trim condition changed, and thus the required control input changed – apparently this was not understood.
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Old 12th Dec 2011, 20:33
  #754 (permalink)  
 
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I didn't visit this thread for . . . . .months/pages, as I have already made MY mind up (as a Boeing -tractor driver) what may have contributed to this almighty cock-up.
Jumping back in after so long , you are the only post on this page, & you have said it all in a few lines. Thanks for such brevity/accuracy
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Old 12th Dec 2011, 20:36
  #755 (permalink)  
 
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Second....
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Old 12th Dec 2011, 20:47
  #756 (permalink)  
 
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Shy talk, et al,
If he'd had a yoke, the others could have more quickly grasped what he was doing.”
See #760. The problem was not directly with what the pilot flying was doing, and the other pilot might see, it was the resultant aircraft flight path. By focusing on the controls, the crew could easily have deduced a control failure – the aircraft did not responding.
The presence of a yoke, coupled side stick, or any other control is unlikely to have triggered the required change of mindset. The problem was that of what was going on out-side of the aircraft and not inside. Excepting of course for the human abilities to assess and understand the situation which required a change of control input.
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Old 12th Dec 2011, 20:47
  #757 (permalink)  
 
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PEI

Two things. First, I did not mean for my last comment to be so LOUD. I edited in a ....NO? But forget to send.

Secondly, I mean for all my comments to isolate the first 10-20 seconds of the Manual Flight regime. Once Climbing, the discussion is to me unhelpful.

The conditions are so negatively serendipitous that I believe almost everyone here cannot fathom the challenge. So it galls me that so many here presume to be so skilled that the crash would not have occurred.

Apology One:

PEI: I have read your input on these pages many many times, and I appreciate your point of view. I apologize if my comment, in its shrillness, may have been taken as doubtful of your pov.

Apology Two:

HazelNuts39: I assumed your graph was a reprint of something BEA had produced, not original work based on BEA data. As such, the lack of respect I showed was based erroneously on mistaken genesis.

Mea Culpa. You have my utmost respect for your no nonsense input, and its quality is unassailable.
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Old 12th Dec 2011, 22:02
  #758 (permalink)  
 
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Amen ! but for the DGAC/Airbus to accept the blatantly obvious, it is also (prohibitively) expensive. . . . . so you & I (and anyone who cares to agree with us) are wrong. . . . OK ?
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Old 12th Dec 2011, 22:23
  #759 (permalink)  
 
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In the first 10 seconds after taking control, the PF wasn't holding full aft stick. his stick movements were between 1/4 and 1/2 aft, while moving full travel left to 3/4 right and letting pitch increase to 11.5 degrees NU.
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Old 12th Dec 2011, 22:24
  #760 (permalink)  
 
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Originally Posted by shy talk View Post
If he'd had a yoke, the others could have more quickly grasped what he was doing.

Surely, no-one can argue with that.
Not in one sense, but I would argue that it isn't understanding what he was doing (pulling back) that is important, but understanding the consequences of that action on the a/c.

The aviation accident record is littered with the smoking craters and floating wreckage of stalled yoke-equipped planes. Planes which crashed with PF pulling back into and through the stall. Surely in those cases, "the others" must have grapsed what PF was doing ?

I would argue that yes they did, but it didn't help. They grasped "pulling back" (doing) but they did not grasp "stalling the a/c" (consequence). Or to put it another way, what would you say the Colgan PNF "grasped" about what PF was doing (pulling back) when she took action to pull the flaps up ? Stall ? or "climb" maybe ? [Yes, he might have been thinking "tail stall", if you believe that theory, but only he had seen the tail stall video and the flaps was without his command, so can't be that]


Now back to 447, where was it lost ? In the climb (I'm with Lyman on this). Once stalled, in poor conditions and without visual reference, their chances (I think) are already slim.

So, did lack of visual control feedback prevent PNF grasping what PF was doing in the climb, thus resulting in the stall ?

Nice theory, but no. PNF knew PF was climibing, he also knew PF shouldn't be climbing and told him to descend. More than once. Had PF followed that instruction they'd probably still be alive.

The fatal problem is not that PNF didn't get what PF was doing at the critical time, it is that neither of them grasped the consequences of that action, despite all the warnings and instrument indications of stall. Why they failed to grasp that is a very very interesting question, but it has nothing to do with stick, because PNF knew PF was climbing - crystal clear from the transcript.


[ I'm excusing the captain at this point - he comes back in when the a/c is already so far beyond tested and simulated flight envelope that systems are going wrong all over the place, and he's fed a history that is well on the misleading side of useless. ]
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