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Old 12th Apr 2013, 16:59
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predictorM9
 
Join Date: Jun 2011
Location: France
Age: 39
Posts: 17
stall recovery in AF447

I just read the leaked (French) experts report on AF447 (I won't put the link here, just google it) and it explicitly mentions that the plane may not have been recoverable at all because of the alternate 2b law, which limits the deflection of the elevator when the stick is full nose down deflection. They showed that even when one of the pilots put the nose down for two seconds (and then neutral) the elevator did not move much.

As a contribution factor of the accident, the report states:

6.4: alt2b flight law, which is hybrid, does not guarantee longitudinal stability for speeds below the stall speed (VS1g)

6.5: The auto trim of the THS is not deactivated below the minimal flight speed (VLS) in alt2b flight law.

Based on these, I think the flight crew was probably in an unrecoverable situation (no matter what they would have done), unless maybe deactivating the ADRs to go into direct mode (as in the recent EVA air incident).

Being a faculty in systems engineering (on a totally unrelated domain), I am shocked by these conclusions. The A330 cannot stall in normal mode, but why do we need a crash to understand that the ALT2B mode is putting pilots into trouble during a stall? They must have done tests during certification. I'm sure they must have stalled the plane in alternate mode to see how it worked...

I know that pilots are to blame etc, but this sheds a different light. Even if the pilots had been professional test pilots, maybe the plane would still have been irrecoverable.
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