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Old 21st Jul 2009, 15:46
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Hyperveloce
 
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Stall warnings & corrupted airspeeds

From what was said, can we conclude that stall false alarms are a very natural outcome from an ADR disagree ? (and the subsequent alternate law 2). It may go hand in hand with overspeed alarms in certain cases.
If we assume there is a high probability that the AF 447 may have been subjected to false alarms, we could then try to figure out how a pilot could react to these stall alarms given the known contextual elements. Or try to find past cases of false alarms of stalling and the associated crew reaction. There are basically two main possibilities: either the crew discard the stall alarms and do not consider them as justified, or the crew makes the opposite choise ? The first possibility would lead to something similar to the Air Caraïbes scenario (not exactly the same though). Don't you think we should explore the second scenario ?
Jeff
PS) We could assess the aerodynamic margins as a function of time from this opposite crew decision & action (beyond whether a pilot could take this opposite decision or not given the context), to try to see how long could it take from the initiation of an overspeed situation to a loss of aerodynamical control, how much time the crew had to recognize and correct this situation gradually leading them out of the flight envelope, to get some timing references. We could try to see which were the clues or indicators that crew may have relied upon to make a correct assessment of the situation, even in the absence of airspeeds (taking in account past cases, we can also make hypothesis so as to the Pitot freezing event duration, or the time when the airspeeds may have recovered their normal values). We can compare this timeline to the ACARS sequence chronology (keeping in mind that the PRIM and SEC failure at 02:13Z may result from an intentional crew attempt to reset the faulty Master flight computer to regain the normal law for the rest of flight).
We would need inputs from experienced pilots for the crew reactions to the multiples signals given the context.
PPS) The Birgenair flight 301: Pitots problems due to maintenance, corrupted airspeeds, false overspeed alarm, and high altitude stall:
http://www.youtube.com/watch?v=vDd2fL5XYSA&feature=related

Last edited by Hyperveloce; 21st Jul 2009 at 23:08. Reason: the post-post-scriptum with Birgenair flight 301 case
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