From BEA's Second Interim Report on AF447:
... as the ATSB mentions in its second interim report(3) on the incident to the A330-300 that was performing flight QF72, in relation to problems with ADIRU’s, the maintenance messages relating to the events on flight AF447 and flight QF72 show significant differences, both in their sequence and in their content.
The accident during flight QF72 was caused by an as yet unidentified fault in one ADIRU, which produced 'spikes' in multiple parameter output signals, in particular that of angle of attack. There is indeed no basis for assuming a similar fault in flight AF447.
On the other hand, there was no anomaly in the way the flight control computers reacted to the faulty AoA signal: the response to a 'high AoA' signal was apparently 'as designed'. As described in the ATSB report, that response was the simultaneous activation of two effects: the high AoA protection (alpha prot) nose-down elevator command of 4 degrees and the high Mach anti pitch-up compensation of 6 degrees. The 10 degrees of elevator movement resulted in the airplane pitching to 8.4 degrees nose-down and a negative normal acceleration of 0.8 g. From the ATSB first Interim Report:
If the PRIMs detected that the aircraft’s AOA exceeded a predefined threshold, the computers would command a nose-down elevator movement to reduce the AOA. (...) Anti pitch-up was a pre-command included in the control laws to compensate for a pitch-up at high Mach due to aerodynamic effect. The compensation was available above Mach 0.65 and when the aircraft was in a ‘clean’ configuration (that is, with the landing gear and flaps retracted).
I doubt if an updraft would cause the airplane to pitch up. The immediate effect of an updraft is to increase the AoA, as shown in the graph I posted in #2664. Since the airplane is aerodynamically stable, it tends to return to the AoA for which it is trimmed, i.e. pitch down. Perhaps more important is how the systems respond in an updraft. The A/P, if engaged, will command pitch down to regain the commanded altitude. Stall warning occurs at an AoA of about 4 degrees
(in alternate law). I wonder at what AoA the two effects observed in QF72 would occur. The yellow triangle in my graph
at about 5 deg indicates 'buffet onset', which is also 'alpha max', corresponding to Vs1g at 1 g. Is this where 'alpha prot' attains it maximum authority? Should BEA look more closely than ATSB has done into the AoA that triggers the 'anti pitch-up' command?
Suppose that all this happened just prior to the loss of airspeed data, how would the pilot(s) react?