Hi,
Originally Posted by Belgique
........c. If the accumulation/compaction rate was sufficiently subtle (i.e. slow) then the effect would be insidious. Thinking here that the speed loss seen by the system would not be actual but would be acted upon by autothrottle incremental increases, thereby putting the constant airspeed/mach (but actually accelerating) aircraft ever closer to the corner of the coffin corner envelope at that height.
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When, in turbulence perhaps, the aircraft actually hit that critical mach (that you must avoid), what happened then?
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Did the autopilot disconnect? Did the pilots assume a coffin corner aerodynamic stall (because they were seeing a low IAS), and then take stall recovery action (lower the nose/cob the throttles?).
The main problem with such scenario is that it just doesn't fit with ACARS reported:
1. Pitot Probes freezing was actually detected by the systems;
2. Auto Pilot and Auto Throttle also disengaged automatically as a consequence of 1 (as designed, and it was not a manual disconnection).
How the pilots reacted is certainly open to speculation but nothing is telling us at this point that an insidious freezing was an issue for the system to change any of the flight parameters. So an upset due to speed issues is very less likely to have happened by itself if it was the only factor in cause.
S~
Olivier