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AF 447 Thread No. 12

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AF 447 Thread No. 12

Old 2nd Oct 2014, 13:27
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Originally Posted by PuraVidaTransport
...you see the yolk in the laps of the pilots?
Horrifying. You have no idea how difficult it is to get dried egg out of the crotch of your uniform trousers...

More to the point it's not a "hole in the cheese", as there is no proof that connecting the things would have made a difference, and pilots have, on several occasions, ignored a yoke that was where it shouldn't have been - they are trained to look *through* it, not *at* it.
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Old 2nd Oct 2014, 14:04
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thf:
Before the stall: The biggest puzzle, in my opinion, is Robert. He did notice that Bonin was behaving erratically. But he didn't follow up on that thoroughly enough. Why not? Langewiesche has the idea that, when Bonin took away his control immediately after Robert took over, Robert didn't notice this and wondered why his sidestick didn't work. Maybe that is a clue: Did he think his machine was uncontrollable even before it really was? If you want to question unconnected sidesticks, I think that would be the moment.
You are addressing a bedrock CRM issue: one pilot flies, the other monitors/assists. If they were, in Airbus fashion, "fighting over the controls" ... either the controls "sum" the conflicts or the "take command" function returns to Bonin (per how AB designed the interaction between the two side sticks), then your point on Robert being cut out of the loop (and hence calling the Captain?) goes to the heart of a CRM and cockpit gradient issue far more than a flight control style issue. (That, and at least one instrument scan that was broken/behind).

More troubling for AF than for Airbus, in some ways.

The further mess of going so far into stall that stall warning was disabled (AB design feature), lack of an AoA gage (done to death back in the original threads) and the return of a stall warning when AoA was again alive ... if they even acknowledged stall warning as other than spurious ... combined with the most recent "condition/response" training for approach to stall being the "down low/near the ground" scenario ... puts a lot of conflicting and non-normal things saturating the crew's awareness at the same time in a scenario I doubt either had seen in a sim.

Small wonder that at least one of them was confused.

Captain Dubois had quite a bit to clean up and sort out when he arrived on the flight deck and tried to figure out what these two had done to his plane when he left them alone together, in cruise, straight and level, a short while before that.

Last edited by Lonewolf_50; 2nd Oct 2014 at 19:50. Reason: A few words were missing that made it look silly
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Old 2nd Oct 2014, 20:14
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@LW_50:

Hullo sir - I do in general agree with what you're saying. If you don't mind a bit of clarification though, the stall warning was not explicitly "disabled" by the logic, it was more a case that the stall warning cannot function without reliably functioning AoA vanes, and the AoA vanes cannot function reliably without at least 60kts forward airspeed. While this scenario is part of the Airbus design spec, there has been a curious level of silence from other builders with regards to whether their current systems run to a similar spec or not. One might suppose that if a better spec existed from another manufacturer, they would have said so by now.

As I recall the discussion from the earlier threads, it quickly became apparent that this particular scenario is rather difficult to solve for every possible permutation of circumstances. The concept of "no warning is preferable to a false warning" is a reasonable one, but it seems that few thought it likely that one could apparently drop below 60kts IAS in mid-air, then come back to it from behind and reactivate the warning.

As for "fighting over the controls" - the only "DUAL INPUT"s happened towards the end of the sequence. As you state and I mentioned earlier, Bonin verbally handed over control to Robert more than once and both times silently took priority back. Robert's priority button would have changed to red in that instance, but in the heat of the moment it wouldn't be a tricky thing to miss.

I ask everyone to have another look at Fig. 64 and see what they think about the following points:

It may be possible that the roll direct aspect of Alt2B might have thrown Bonin initially, but consider these points:
  • Bonin had *no* training or experience in high-altitude manual handling in Normal Law, let alone any of the Alternate configurations - how could he have known what to expect (put another way, how could he be 'thrown' or 'confused' by the control law change when he had no prior experience with which to compare it)?
  • Take a close look at the "Lateral Wind" graph alongside the pink trace on the "Roll Attitude" graph. At the moment Bonin took manual control, a 25kt right crosswind with an updraft component suddenly dropped sharply. The pink trace indicates that even with no input, the simulated aircraft actually rolls about 2 or 3 degrees to the left from inertia.
  • The right crosswind returns and averages around 30kts for the next 12 seconds, but at this point, Bonin's initial overcontrol to the left has him disorientated and making input reversals.
No matter what control law you are in, or even if you're in a type with traditional controls, I'd imagine that kind of initial quick reversal would be very tricky to damp out manually, and practically impossible if you've just been handed control from the AP with little warning. The return of a near-constant right crosswind for the next 12 seconds can only complicate matters further.

Penny for anyone's thoughts?

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Old 2nd Oct 2014, 22:47
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it was more a case that the stall warning cannot function without reliably functioning AoA vanes, and the AoA vanes cannot function reliably without at least 60kts forward airspeed
At at least 60 knots forward airspeed we can suppose that a A330 (if in the air) is stalled (or no more what is called "flying")
Can we agree on this ? (I suppose yes)
So .. why (under the reason that AoA vanes cannot function reliably at this speed) stop the stall warning alarm .. as other parameters (but maybe not show or seen by the pilots) indicate a stall condition
I don't catch the logic of this one !
As I tell already before .. this will be a debate ( like here ) about this (and certainly other Airbus things) .. on the trial
Wait and see for the results ...

Last edited by jcjeant; 2nd Oct 2014 at 23:00.
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Old 2nd Oct 2014, 22:49
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Originally Posted by thf
Before the stall: The biggest puzzle, in my opinion, is Robert. He did notice that Bonin was behaving erratically. But he didn't follow up on that thoroughly enough. Why not? Langewiesche has the idea that, when Bonin took away his control immediately after Robert took over, Robert didn't notice this and wondered why his sidestick didn't work. Maybe that is a clue: Did he think his machine was uncontrollable even before it really was? If you want to question unconnected sidesticks, I think that would be the moment.
Not too sure about that as the airplane was already stalled when Robert took control.
That being said, not knowing how Bonin was actually dealing with the sidestick, he possibly lost trust in the FCS integrity so asked Dubois to switch off or reset some FCCs.

Originally Posted by PJ2
It is a common one when doing various tests within a Just Culture, but I think it is particularly relevant here when we're trying to sort out ways of examining cockpit behaviours, ergonomics and human factors. What it helps do in normal practise of airline work is place issues succinctly before those who must manage a Just Culture on a day-by-day basis and handle events which their airline's safety and data programs present, some of them serious. They are examining the "incidents" before they occur, so to speak and this is one way to sort out which way to focus when fixing a problem that is emerging in the data.
Airbus missed the opportunity to apply that Just Culture :
http://www.pprune.org/7450265-post576.html
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Old 2nd Oct 2014, 23:10
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At at least 60 knots forward airspeed we can suppose that a A330 (if in the air) is stalled (or no more what is called "flying")
Can we agree on this ? (I suppose yes)
So .. why (under the reason that AoA vanes cannot function reliably at this speed) stop the stall warning alarm ..
I don't catch the logic of this one !
I doubt the designers ever envisioned a scenario where an aircraft "in-flight" could be traveling less than 60 knots (it's even hard to envision now knowing that it happened).
On some of the older Boeing aircraft the engine control uses airspeed as a defacto air/ground indication (using something like 120 knots or Mach 0.2, with hysteresis, for the threshold).
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Old 2nd Oct 2014, 23:15
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Originally Posted by jcjeant
At at least 60 knots forward airspeed we can suppose that a A330 (if in the air) is stalled (or no more what is called "flying")
Can we agree on this ?
If all the sensors are functioning normally, sure - but you have to design for the possibility that they won't be. Prior to this accident, an apparent IAS of less than 60kts would likely have been considered far more likely to be a sensor failure than an actual occurrence (as tdracer alludes to above). So, no, can't necessarily agree.

Originally Posted by CONF iture
he possibly lost trust in the FCS integrity so asked Dubois to switch off or reset some FCCs.
Aside from the fact that there's nothing to suggest this in the slightest on the CVR.

Airbus missed the opportunity to apply that Just Culture :
http://www.pprune.org/7450265-post576.html
The majority of the contents of the "Red OEB" you say should have been published in your linked post were already covered in the UAS procedure included as part of the report (Annexe 06):
http://www.bea.aero/docspa/2009/f-cp...nexe.06.en.pdf

What difference would the OEB have made (AFAIK a "Red" OEB would have required an AD - something which AF would probably have pushed back on)?

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Old 3rd Oct 2014, 00:36
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At at least 60 knots forward airspeed we can suppose that a A330 (if in the air) is stalled (or no more what is called "flying")
Can we agree on this ? (I suppose yes)
yes, the disagreement is for compliance of the stall warning

25.207 Stall warning
(c) Once initiated, stall warning must continue until the angle of attack is reduced to approximately that at which stall warning began
More over, FBW algorithm does not meet the Federal Aviation Regulations Part 25 for static longitudinal stability,
which requires a pull force to achieve and maintain a steady state speed decrease relative to the trim speed and vice versa Also, after having released the stick, the speed has to return to the trim speed.
Therefore, for this reason, I strongly believe that the awareness of the crew with respect to the stabilizer position is vital, as well the active sidestick that provides awareness for out of trim and the mushy feeling at low speed or stall.
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Old 3rd Oct 2014, 01:57
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Penny for anyone's thoughts?
The simulation for hands off is highly speculative. Yes, it used the winds that the aircraft encountered (apparently) BUT the simulation results in an aircraft in a ~ 10 degree right bank on average which will have the effect of circling the aircraft back toward the storm and in any case, on a different path than AF447 took to get where it ended up.

To properly run the hands off scenario, about the best one can do is to do a long series of simulations with random turbulence injected to see where the most probable result lies. Maybe there was a fortunate circumstance in the data used to create the simulation and in reality the spiral dive would dominate the results. One thing you can hang your hat on is that the resultant flight path in Fig 64 is only a speculative path that starts with closely similar winds aloft and diverges from what would have been encountered had the hands free course been taken.

Dozy's statement that the AOA vanes cannot measure below 60 knots is not strictly correct in that it is not the vanes that are the limitation, but the down stream electronics that are processing the signal. Az33ab provided that information several times. Apparently that same box is also used on other non-AB aircraft so the problem is broader in scope than just Airbus.

With regard to Roberts lack of assertiveness, just how long did he have after being summoned back to the cockpit? Perhaps we are reading too much into his words when he said he had he had grabbed a little bit of sleep. Perhaps he had awakened out of a deep sleep and didn't really trust himself yet.
One of the things that used to scare me, (but there was nothing to be done about it) was sleeping in the cockpit while strapped in on 5 minute alert on the flight deck of an aircraft carrier. When the alert sounded, you knew that the catapult would be firing you off the deck within 5 minutes. I wasn't sure I would be up to the task but the flight schedule didn't give you sufficient opportunity to sleep otherwise. Perhaps crew members need a certain amount of time to come up to speed after they have been sleeping. Did AF have a clear cut procedure that spelled out how long must be given before putting a sleeping pilot back in control. Think of the Mangalore B-737 accident. The Captain had been sleeping in his seat for over 1.5 hours , and was awakened just in time to do the approach which he butchered and caused a high speed overrun accident.
Sleep is one of those things that is necessary but needs careful management because it has such a strong effect on human performance if mis-managed.
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Old 3rd Oct 2014, 01:58
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Hi,

Dozy
If all the sensors are functioning normally, sure - but you have to design for the possibility that they won't be. Prior to this accident, an apparent IAS of less than 60kts would likely have been considered far more likely to be a sensor failure than an actual occurrence (as tdracer alludes to above). So, no, can't necessarily agree.
Now that all (by all I mean the entire world!) know that it is possible that pilots themselves can put a aircraft in a situation resulting a airspeed at 60 knots or even under (and with all censors working fine .. except the speed censors for a limited time) what Airbus (or regulators) will change regarding stall alarm .. as all we know that history repeats itself even in the world of aviation
A Chinese proverb says
For know your future look back

Machinbird
Dozy's statement that the AOA vanes cannot measure below 60 knots is not strictly correct in that it is not the vanes that are the limitation, but the down stream electronics that are processing the signal
Of course but what about the "Stall Alarm" ?

Machinbird
The simulation for hands off is highly speculative. Yes, it used the winds that the aircraft encountered (apparently) BUT the simulation results in an aircraft in a ~ 10 degree right bank on average which will have the effect of circling the aircraft back toward the storm and in any case, on a different path than AF447 took to get where it ended up.
Hand off
So when on a flightdeck .. begin the music (a concerto!) of alarm of all kind (like it was on the AF447) the answer is hand off ?
With insight for this particular case.. maybe yes ...
In reality .. certainly not !

Last edited by jcjeant; 3rd Oct 2014 at 02:12.
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Old 3rd Oct 2014, 06:18
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@Machinbird

I tend to disagree when you suggest the hands off calculation is highly speculative.
The excellent match between DFDR and the hands on calculation shows that the wind/gust/control combination was accurately measured, and from there to a hands off state is a simple subtraction of the response to the control applied.
If AI can't calculate that accurately then you won't have any approved simulators.
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Old 3rd Oct 2014, 07:33
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The hands off simulation demonstrates two points within the initial first minute of the upset:

The pitch excursion was caused by Bonins initial pitch input
The roll excursion was worsened in frequency by Bonins attempt to level the wings.

While the pitch excursion only manifested itself for Bonin in an increased pitch indication and a steady climb rate (if he noticed those), the roll excursion was changing from left to right (like wing rocking) despite the inputs Bonin made.

That's Machinbird's point, which i share. Bonin was obsessed in geting the roll under control, causing PIO by his inputs in roll direct, and thus not gave much attention to the pitch excursion.

Last edited by RetiredF4; 3rd Oct 2014 at 07:46.
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Old 3rd Oct 2014, 12:36
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Pitch Versus Roll inputs.

I fly 319/320 s and have a couple of years on 340 s. During manual flight whilst Pilot not flying I've noticed some pilots inducing roll whilst intending to pitch the aircraft and vice versa. Why?

I started checking their control inputs during the control checks on the ground and every time their roll inputs also induced pitch inputs ie ailerons full left and there would be some up elevator, ailerons full right and there would be some down elevator. Once I brought it to their attention and they adjusted their hand wrist positions and tried again (calibrated their senses) so that they could make "pure pitch" and "pure roll" inputs things went a lot better during manual flight.

It would be interesting to see what the flying pilots last manually flown approaches looked like in respect of pitch and roll inputs.

For non Airbus pilots - your seat armrest position is critical so that your inputs are correct, if the armrest is forgotten up accurate inputs to the side stick are virtually impossible as you are making inputs with your arm instead of your wrist. If the armrest is down but not setup for you then it's really hard as well.

Last edited by groundfloor; 3rd Oct 2014 at 12:51. Reason: Grammar, sigh.
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Old 3rd Oct 2014, 12:57
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groundfloor

An excellent observation, which very plausibly might have a bearing on this incident. Pilots swap positions and/or don't bother to adjust the chair properly. Aircraft on autopilot and no expectation of having to take manual control before the next changeover. Easy to visualise this happening.
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Old 3rd Oct 2014, 14:38
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Originally Posted by CONF iture
Not too sure about that as the airplane was already stalled when Robert took control.
You are right, it is at 2:11:37, on the way down, not at about 2:10 as I had remembered. Shame on me for trusting a journalist.
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Old 3rd Oct 2014, 16:23
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I tend to disagree when you suggest the hands off calculation is highly speculative.
The excellent match between DFDR and the hands on calculation shows that the wind/gust/control combination was accurately measured, and from there to a hands off state is a simple subtraction of the response to the control applied.
If AI can't calculate that accurately then you won't have any approved simulators.
Hi Owain,
I am not commenting on the accuracy of the measurements implied. I am commenting on using those measurements in a situation where you are computing the effects on a theoretical aircraft whose flight path diverges from the known flight path.

If the the aircraft averages ~10 degrees wing down for the duration of the simulation, then it will be flying through a different part of a turbulent air mass, and the assumptions used to develop the effect on the aircraft will diverge from what would have happened in reality as time increases.

I think everyone would be better served by a Monte Carlo simulation of the possibilities so that we could better understand the aircraft's natural tendencies and the factors required to make it diverge substantially from those natural tendencies.
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Old 3rd Oct 2014, 17:01
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Originally Posted by groundfloor
It would be interesting to see what the flying pilots last manually flown approaches looked like in respect of pitch and roll inputs.

For non Airbus pilots - your seat armrest position is critical so that your inputs are correct, if the armrest is forgotten up accurate inputs to the side stick are virtually impossible as you are making inputs with your arm instead of your wrist. If the armrest is down but not setup for you then it's really hard as well.
Actually his inputs on the departure up to the point where A/P was engaged should be available on the DFDR record, but that was not released in the accident report.

Going back to grity's stick movement chart.

The first point I would like to make is that the initial stick move which begins at 7 seconds is not just lateral but is instead diagonal to the left and aft. Sort of a wrist curl leading to a further finger push to the left. This would be too early in the event to be making a conscious decision to climb the aircraft as part of a procedure. He must have been in reaction mode, not a planning mode.



At that point in time, all Bonin knew is that the autopilot had dropped out and that the aircraft needed a roll correction to the left. The reason for the aft stick could be explained as simultaneously trying to pick up the nose to regain the indicated 300 or so feet lost when the airspeeds were rejected, but in actuality, that probably is not the reason!

Consider this. If Bonin is a stick pulse correction type pilot, why is he maintaining the stick almost exclusively in the range of 4 to 8 degrees aft stick while making mostly large (pulsing) lateral corrections?

This suggests that his inner tension was being reflected as an inadvertent aft stick pressure. (Never mind, Dozy, if it takes a fair amount of force to do this, we are talking about a guy who is really on edge already and has just fallen into an unfamiliar flight condition) The adrenaline is kicking in.

Then finally at 15.9 seconds and at 17.2 seconds, he begins making nose down pulses while traversing the stick to the right. Finally! A pitch motion that seems in character with his assumed style of flying. Does that prove the almost constant aft stick position was inadvertent. No. But it sure does suggest it.

This is why I would greatly like to see the DFDR traces from the period just after the takeoff to further characterize his style. How can we get access to the initial manual flight portion of the DFDR record? Who do we write to? Is BEA free to release it or is it now up to the court?
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Old 3rd Oct 2014, 18:16
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@Machinbird


[If the the aircraft averages ~10 degrees wing down for the duration of the simulation, then it will be flying through a different part of a turbulent air mass, and the assumptions used to develop the effect on the aircraft will diverge from what would have happened in reality as time increases.]


In that of course you are entirely correct, although the major difference I think would come from the different winds at different altitudes. I do think though that there is enough meat in the simulation to show that the aircraft, left to itself, would have stayed safe, which is why, I think, the simulation was attempted.
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Old 3rd Oct 2014, 19:39
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Originally Posted by _Phoenix_
More over, FBW algorithm does not meet the Federal Aviation Regulations Part 25 for static longitudinal stability
Not in the strictest sense. In Normal Law, the aircraft has neutral longitudinal stability. Outside of Normal Law, the EFCS is configured to provide a form of longitudinal stability in concert with low energy warnings.
http://easa.europa.eu/system/files/d...Airbus_340.pdf
http://www.caa.govt.nz/aircraft/Type..._A320_A321.pdf
http://www.caa.co.uk/aandocsindex/22733/22733000000.pdf

There were special dispensations based on certification tests, which all regulators (including the FAA) approved.

There's a nice summary of the Airbus EFCS here: http://www.davi.ws/avionics/TheAvion...ook_Cap_12.pdf

Remember that the trim did not move of its own volition - it moved because the pilot input was commanding it to move. In fact, had Robert looked to his right during the minute the trim was rolling back in response to Bonin's sidestick, he may not have been able to see the latter's sidestick, but he'd definitely have been able to see the trim wheel moving. There is a trim position indicator on the wheel which would have told them their trim position had they looked.

Originally Posted by Machinbird
This suggests that his inner tension was being reflected as an inadvertent aft stick pressure. (Never mind, Dozy, if it takes a fair amount of force to do this, we are talking about a guy who is really on edge already and has just fallen into an unfamiliar flight condition) The adrenaline is kicking in.
That's one possibility, as is Franzl's suggestion regarding 'tunnel vision' on roll - but as always I'd urge caution on terms of reading too much into things. The fact is that we cannot know for certain what was going through his head, and that fact is as immutable as it is frustrating.

But it sure does suggest [inadvertent back pressure].
Again, it's possible - but as I said before though, his explicit reference to being "at maxi nose-up for some time" implies otherwise.

So what we're left with includes these possibilities (please add any I've either forgotten or don't know):
If inadvertent:
  • He may have had his seat/armrest positioned badly, and induced a pitch component to the input
  • He may have been "tensing up" from adrenaline with the same response

If deliberate:
  • He may have been trying to follow the intermittent FDs
  • He may have not heard and/or realised the consequences of Robert's "Alternate Law" callout, and assumed the hard protections were still there
  • He may have fixated on the risk of excessive speed or overspeed from the outset, and been trying to mitigate that risk by using pitch to slow the aircraft

My personal opinion, for what it's worth, is that the last point (i.e that it was intentional and he was fixating on excess/overspeed risk) is the most plausible - though again, I should add the caveat that it's an educated guess and certainly not a done deal. So why do I think it most likely?
  1. The "crazy speed" comment, followed by his attempt to deploy speedbrakes, is the most obvious indication that he's concerned about overspeed
  2. This happens about a minute and a half into the sequence, but if you look at his comments prior to this, there's a distinct impression that he's been concerned about overspeed for some time ("We don't have impression of speed", "TOGA", "I'm in TOGA eh")
  3. He's been sounding nervous about transiting the weather and potential turbulence since before Capt. Dubois went to rest - IIRC standard procedure in turbulence is to reduce thrust and slow down to reduce risk of airframe stress
  4. He's likely aware that the THR LK function has been disabled with the TLs in CLB, which goes contrary to the principle of reducing thrust and slowing down
  5. Thrust is then set to TOGA, which goes further contrary to that practice
  6. He's a glider pilot, so how do you reduce speed? Pitch up.
  7. Possibly due to concentrating on damping the roll, he seems to be unaware of the climb he began with the pitch up, and the stall regime begins to creep up just as he gets the roll under control
  8. The SW sounds, but he's still in the "overspeed" mindset (similar to the case of the Birgenair 301 Captain), and either does not hear or disregards it
  9. The stall condition becomes fully developed and the aircraft begins to descend. When the descent becomes established, Bonin's stick soon becomes slammed against the backstop for almost a minute
  10. Nevertheless, the aircraft does not climb - and furthermore, the roll control is lost again
  11. This lack of control response is indicative of stall, but similar unusual control responses can also be indicative of overspeed
  12. If Bonin did not notice the extent of the pre-stall climb (which he does not mention on the CVR), but he's aware that they've been at higher than normal thrust settings for nearly two minutes (which he refers to twice on the CVR) - he's already set up his mental model with an expectation of overspeed

From this point on, the lack of cohesion on the flight deck becomes terminal. Bonin clearly thinks they're in overspeed, but Robert, in choosing to wait for the Captain, is second-guessing his own SA by the time he returns. Neither Robert nor Dubois offer an alternative explanation for the situation to Bonin, so in the back of his mind he may still be thinking "overspeed" and reacting accordingly.

This is all supposition on my part, but it seems like a fairly logical progression.

@Winnerhofer - there is no useful "car" analogy to that situation. ABS works by using sensors to detect zero wheel rotation when braking is applied at any speed.

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Old 3rd Oct 2014, 21:38
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I started checking their control inputs during the control checks on the ground and every time their roll inputs also induced pitch inputs ie ailerons full left and there would be some up elevator, ailerons full right and there would be some down elevator. Once I brought it to their attention and they adjusted their hand wrist positions and tried again (calibrated their senses) so that they could make "pure pitch" and "pure roll" inputs things went a lot better during manual flight.
I'm not a pilot and this could be a load of rubbish, but perhaps the control laws play a part as well. You're taught on 'traditional' aircraft which require back-presure (pitch) to maintain altitude when rolling. Maybe this sub-conciously transfers over to the Airbus?
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