AF 447 Search to resume

[Chris Scott]

Quote from HN39:
All things combined, the conclusion could be that it is not likely that the airplane stalled at 2:10, and remained stalled all the way down to the surface.

Agreed. Perhaps I can chip-in to offer a few related observations I've been chewing over for a while, at risk of re-stating the obvious (or needing correction).

Prior to 0210z
(a) 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 seems unlikely, though not impossible.
(b) Alpha-Floor was available, looking at alpha (not speed), and its intervention would have generated warnings.
(c) 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 individual ASIs or between the 3 ASIs (although the relevant failure message later transmitted by ACARS would not have been displayed to the crew).
(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. If the former, Thrust-Lock would have maintained the N1 at time of disconnect.
(4) Flight controls degrade to Alternate Law (thought to be be ALTN 2). On both pilots' PFDs, therefore, speed protection bands and indices re-configure on ASIs, and "Speed Lim" flags appear; bank-angle protection marks on attitude indicators change to amber Xs.
(5) Alpha-Floor protection is lost (meaning the crew would have to order TOGA thrust for any stall recovery).

I think most of us believe that an upset sequence started between 0210z and 0211z, or very soon after: perhaps while the crew started to realise that they had no reliable speed indication, and were attempting to establish a thrust/pitch regime; perhaps due to severe vertical windshear during this change of modus-operandi. As I think HN39 has stated, the aeroplane would have taken a long time to slow down to the stall.

Prior to 0210z, it seems unlikely the speed would have fallen seriously except in the event that the crew were not monitoring AND all 3 pitot-heads iced-up in concert to produce false, but similar, over-readings. The latter seems implausible.

To sum up: it seems unlikely that the initial upset involved a stall.

Chris