it seems that the A/C could have exited its flight enveloppe underspeeding or overspeeding once the A/P & A/THR gone OFF. but I also feel that a large excursion in the high mach numbers (overspeed) take some time to become critical (see
http://www.pprune.org/5102068-post4106.html for a basic/not validated attempt to get an idea), even descending at 1 or 2° with N1=95 or 100%. In past cases, 5 crews reacted to stall alarms by a nose down and a descent, -3500 ft max. but if there were increased turbulences close to the Cb cell and/or a turn to avoid a weather hazard, maybe the aerodynamic margins were further narrowed ? I thought that the overspeeding possibility was more probable / explainable given the known conditions/procedures/past cases, but if the plane is really south of LKP (so far from its route) close to the region where the pingers were detected by the French Navy & Thales, then the high altitude upset (in alt2, no alpha prot, no low speed stability) must have been more sudden/immediate than an overspeeding event ? (at 02:10 or early 02:11, not 02:12 or over). Then the other possibility, the low speed stall (BEA: low index vs the pich remaining locked)(possibly accompanied with a large roll excursion complicating the recovery) would appears more probable if the flight ended around 02:15Z in the pinger area ? in one past case of Pitot freezing the A/THR remained engaged and the N1 was varied between 48 and 100% (airchasing in turbulences ?). And as it was said, a low speed stall at high altitude can turn into an overspeed. Can a low speed stall due to a low N1 (50, 60%) locked occur rapidly from A/P A/THR OFF ? (say less than 20-30s)
Jeff