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AF447 Thread No. 3

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AF447 Thread No. 3

Old 29th May 2011, 20:46
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ChristianJ, I was more or less pleading for something to replace "the pilot did it" with "why did the pilot do it?" Who carries with it implicit blame for the person. Why at least "spreads the blame" to perhaps faulty stimuli, faulty training, he just had a bad day, and other possibilities.

And to be above board at the moment it looks like there is a training gap that may need to be filled and like there is a software design level inadequacy that can lead to stimuli that confuse even well trained pilots. (This latter comes from referencing past events as well as this crash. There is a sage old computing homily worth remembering, "Garbage in, garbage out.")
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Old 29th May 2011, 20:50
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Originally Posted by Minorite invisible
The PF commanded nose up in manual flight, alternate, law. The aircraft was just attempting to trim the aircraft to comply with pilot input. Quite normal.
Agree, but what do you make of the stall warning ...
Let's say you want to practise a full stall exercice on a 757, would you still trim up past the initial stall warning ?
The question is why the automation is doing something you would not ?

That the low speed stability protection disappears in a scenario of unreliable airspeed is logic, but also auto trim should.
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Old 29th May 2011, 20:55
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Originally Posted by JD-EE
This event may end up as a bonanza for the people who make the simulators as more time may be needed for more unexpected events.
As mentioned earlier, the issue there is that there is very little data on the real aerodynamic behaviour of big jets 'outside the envelope'. For simulator purposes, most is just extrapolated from available data (see the NASA report on the subject).
Simulator manufacturers wouldn't mind, but they cannot afford the (highly instrumented and risky) flight testing needed to acquire such data....;
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Old 29th May 2011, 20:58
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Originally Posted by TLB
It has been suggested on one or more of these threads that the corrective action in the event of airspeed failure above FL 100 is: TOGA and 5 degrees pitch.
Not exactly. Its CLB and 5 degrees pitch.

TOGA is only at take-off and below 10,000 feet in the climb
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Old 29th May 2011, 21:04
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Originally Posted by Minorite invisible
A small detail, but one that must be cleared up nevertheless
I agree with your translation.
Basic problem with a "text" description, rather than the actual plots of the actual parameters, which we're unlikely to see before the July interim report, if even then.
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Old 29th May 2011, 21:09
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Originally Posted by JD-EE
ChristianJ, I was more or less pleading for something to replace "the pilot did it" with "why did the pilot do it?" Who carries with it implicit blame for the person. Why at least "spreads the blame" to perhaps faulty stimuli, faulty training, he just had a bad day, and other possibilities.
OK, you put it better than I did.
"Who did it" is the first link in the chain, "why did he do it" is the second.
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Old 29th May 2011, 21:09
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In French, is it not saying "during thirty seconds"?

In Normal Law, a pilot can input full left roll and full aft stick and hold it, without fear, "protections". N'est-ce pas?
 
Old 29th May 2011, 21:10
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As mentioned earlier, the issue there is that there is very little data on the real aerodynamic behaviour of big jets 'outside the envelope'. For simulator purposes, most is just extrapolated from available data (see the NASA report on the subject).
Simulator manufacturers wouldn't mind, but they cannot afford the (highly instrumented and risky) flight testing needed to acquire such data....;
There are several companies that specialize in aerodynamic modeling - I will leave them nameless for now, PM me for details - that CAN extrapolate meaningful modeling (supplemented by wind-tunnel testing to refine) that will provide valid flight model extensions. I have posted several times about the ICATEE RAeS - see RAeS Flight Simulation Group - Introduction to the ICATEE
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Old 29th May 2011, 21:17
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Originally Posted by CONG iture
Agree, but what do you make of the stall warning ...
Let's say you want to practise a full stall exercice on a 757, would you still trim up past the initial stall warning ?
The question is why the automation is doing something you would not ?

That the low speed stability protection disappears in a scenario of unreliable airspeed is logic, but also auto trim should.
Many of these Airbus "protections" are based on speed indication. In an unreliable airspeed situation as we had here, all "protections" and logic can be thrown out the window since the aircraft has no idea what speed its really at.
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Old 29th May 2011, 21:19
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PF/PNF

TLB, I think Pilot B was PF in his usual RHS, and Pilot C took the LHS as the PNF.
Pilot B was at the controls with the airspeed indiction that was not recorded ...
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Old 29th May 2011, 21:21
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Originally Posted by bearfoil
In French, is it not saying "during thirty seconds"?

In Normal Law, a pilot can input full left roll and full aft stick and hold it, without fear, "protections". N'est-ce pas?
Yes, it does say "during thirty seconds"

You are also correct about what would be possible under Normal Law, but the aircraft was in Alternate law, and the pilot knew it for he called it 11 seconds after the autopilot disengaged.
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Old 29th May 2011, 21:24
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Originally Posted by CONF iture
TLB, I think Pilot B was PF in his usual RHS, and Pilot C took the LHS as the PNF.
Pilot B was at the controls with the airspeed indiction that was not recorded ...
Which is backed up by the fact that Autopilot 2 was engaged as per the report.
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Old 29th May 2011, 21:28
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GY & CJ, perhaps what is really needed is a reactions test for something like AP and AT disconnect during cruise. Does the person make the correct action when it happens? That takes care of the er "meatware" part of the equation. The second part of the equation is whether the "correct action" is properly defined.

The really unfortunate thing is spending an hour letting the people in the cockpit relax because sometimes nothing happens during this phase of the simulator check becomes "expensive" quickly. What a person does in real life is not necessarily what she or he does when knowingly facing a test situation.

(That's why I think looking into past experience and the reactions honed there may be well worth it. One tends to go back to "imprinted" reactions when in a crisis. Is extreme mobility between types a good idea or not? Most of the time it is OK, accident records prove this. But when fighting for that extra 9 in reliability speak you look at this type of issue. And this accident is really in the decimal places to the right of the 99. part of the number.)
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Old 29th May 2011, 21:30
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"You are also correct about what would be possible under Normal Law, but the aircraft was in Alternate law, and the pilot knew it for he called it 11 seconds after the autopilot disengaged."

Yes, I am aware, but the PF made his correction in Normal Law, without fear (at the time) of any bad behaviour. The drop to ALT Law found him with a fist full of back stick and roll left? What does he do then? More importantly, what does a/c do? The THS?

thanks
 
Old 29th May 2011, 21:32
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milsabords. It is good that you are exploring these ideas. I don't wish to discourage you unduly. Please consider the below as constructive advice.

"Use of a gas behind the membrane would not work because of PV=RT."

Mariott's law is not a problem: V, R are fixed values. T is measured, so P can be computed
Let me challenge some of the assumptions above. Since the membrane is by definition flexible, is V really fixed? Is T realy uniform?

My personal philosophy in designing mechanisms and devices is KISS.
The fewer moving parts, (or variables) the better.

The law is the ideal gas law (of which the Boyle-Mariotte law is a special case.)

I do not think you would be building on a stable foundation if one used a trapped gas behind the membrane.
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Old 29th May 2011, 21:32
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Minorite invisible, minor correction - it was PNF who made those statements. PF never, in the transcript, replied to the statements. (He may have replied and it was not noted in the partial transcript.)
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Old 29th May 2011, 21:33
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NU input

Originally Posted by CogSim
Why nose-up. Was this required to arrest the roll to the right?
A particularity of the sidestick, depending how you grab it, is that it can be easy to involuntary command a NU or ND input by implying a generous side input.
Was that NU input intentional ...
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Old 29th May 2011, 21:34
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TLB, I think Pilot B was PF in his usual RHS, and Pilot C took the LHS as the PNF.
> Pilot B was at the controls with the airspeed indication that was not recorded ...

> Which is backed up by the fact that Autopilot 2 was engaged as per the report.

Thanks ... that makes sense
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Old 29th May 2011, 21:36
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CONFiture

And "to the stops" infers either confidence or sloppiness. Or, over-reaction.
 
Old 29th May 2011, 21:48
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> It has been suggested on one or more of these threads that the corrective action in the event of airspeed failure above FL 100 is: TOGA and 5 degrees pitch.

> Not exactly. Its CLB and 5 degrees pitch.

> TOGA is only at take-off and below 10,000 feet in the climb

Minorite invisible,
Thanks for that. So my deduction remains: if the PF initially concluded (immediately following AP/AT disengagement) that his main problem (of many) at the time was that he was experiencing an unreliable airspeed situation, the fact that he increased power and raised the nose was exactly the correct response. Non ?
How the aircraft ended up zooming to FL 380 and high AoA is another story.
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