CONF iture:
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Originally Posted by HN39
The curious thing is that the threshold did not change to 10° when the speeds became invalid.
I think the answer is in the FCOM 3.02.34 (also mentioned in the Air Caraibes Note) :
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Rely on the stall warning that could be triggered in alternate or direct law. It is not affected by unreliable speeds, because it is based on AoA.
As you say, the stall warnings ACA got were not false, they were only inappropriate in the way that the crew did very well to ignore them by maintaining a pitch and a thrust setting and not destabilizing that precarious situation.
I must say this ACA note is terrific. Congratulation to Mister HOUANG. Not much to see with the usual bla bla of a BEA report ...
I'd be very interested to hear Airbus pilots' thoughts on what might have happened if the Air Caraibe pilots (for there were 2 almost identical incidents...) had *not* made the quick decision to ignore the stall warnings, when flying through high-level turbulence, with iced pitots, and in alternate law.....
Also, their actions tend to test the general rule proposed above by DeSitter,
All this discussion of what the Airbus FMCs do is interesting, but irrelevant - when humans are confronted by a computer that is either not working, or working in a regime they are not intimately familiar with, they freeze - they go into brain lock.
Which obviously those Air Caraibe guys didn't.....