@OK465
Why would the board glom onto 'alpha floor' as a probable when it's inhibited above 0.53 IMN?
What am I missing here? Has someone else covered this earlier?
The straight answer is that I don't know
Partly because I'm not sure what "alpha lock" entails and partly because the recorded behaviour of the engines is consistent with an 'alphafloor' occurrence regardless of what the book says said about its 0.53M threshold.
The AIB report text is:
Alpha floor is an autothrottle function which applies full thrust, irrespective of the position of the thrust levers, if the airspeed is likely to reduce to a value approaching alpha max
Its all a bit confusing, as the thrust increase came at about the same time, or even a little after, the A/T was disconnected, but the report makes no mention of any throttle increase by the PF, only the thrust reduction. Also the phraseology "if airspeed is likely to reduce to a value approaching alpha max" leaves one wondering! It does imply though that alpha floor switching is also a function of rate of change (of speed?)
Ducking the issue somewhat, I imagine that the AIB will have taken advice from Airbus on what might have been and I would think (well hope anyway) that AI would understand their own system
Edit: OK I now understand what alpha lock is, (prohibiting slat retraction in certain circumstances) but so far as I can see it would in no way be relevant to the cruise condition where this incident occurred.