Originally Posted by
Chris Scott
Quote from HN39:
Prior to 0210z
1) The A/THR was supposed to be controlling speed, and may even have been used by the PF to slow the A/C to turbulence speed. Partial (subtle) loss of thrust (as-per BA038) seems unlikely so early in the flight.
2) Alpha-Floor was available, looking at alpha (not speed), and it's intervention would have generated warnings.
3) AP was controlling the selected pressure-altitude: probably still FL350.
Between 02:10:00 and 02:10:59 (selected events – sequence unclear)
1) Inconsistencies may be apparent on or between the 3 ASIs.
2) Duty AP disconnects: either due to a system failure or a sidestick forced off-centre.
3) A/THR disconnects: either due to a system falure or PF closing the throttle levers.
4) Flight controls degrade to Alternate Law (thought to be be ALTN 2). On both pilots' PFDs, therefore, speed protection bands and indeces re-configure on ASIs, and "Speed Lim" flags appear; bank-angle protection marks disappear from attitude indicators.
5) Alpha-Floor protection is lost.
Chris
I'm with you in the camp that agrees that the poop really left its pile (as you say, "the upset sequence started") at or after 0210. None of the available alternatives make sense-- really, including a stall. It's obviously shocking enough to all of us to have inspired this much discussion.
I guess I have always thought of severe turbulence as being the physical force instigating the upset, with recovery complicated by unreliable or unavailable airspeed information. With autothrottle set at turbulence penetration speed (or Mach?) the commanded thrust varying all over the place to cope with gusts, lateral shear, and vertical shear-- this seems like a phenomenally bad time to have to very suddenly "pitch and power" fly the plane... especially with temperature shears in my assumed CB affecting recorded Mach. But then it's hard to figure out how the plane got from penetration speed to stall speed (or even within, say, 50kts of stall speed) so fast.
I suppose I settle meekly back in to the "wait for the recorders" group. It's like we got every 10th page of a 100 page mystery.