Originally Posted by TheShadow
The above debate disregards where the THS may have been trimmed to and what instantaneous pitch effect it may have had upon the aircraft at autopilot disconnect. That's another ball-of-wax that's unclear to me. i.e. where's the THS being trimmed to when the datum indicated airspeed is artificially low - and how much deflected elevator can the autopilot's baro-hold handle in order to maintain the dialled in flight level (before disconnecting)?
Not far from your comment, the BEA made a note on page 53 of the second interim report :
The reappearance of the flight directors on the PFD when two air speeds will be calculated that can lead the crew to rapidly engage the autopilot. However, these speeds, though of the same order, can be erroneous and weak and thus lead the autopilot to command movements of the flight control surfaces that are inappropriate for the real speed of the airplane.