Originally Posted by
Microburst2002
In case of an AoA failed in such a way that erroneously gives a stall output, the normal law would pitch down to reduece the AoA. Because it would remain fixed, erroneously, FCS would keep pitching down... Or so I believe.
The AoA in Normal Law will be held just short of Alpha Max if Alpha Prot is triggered. An increase in Mach will cause the Alpha Max to decrease - and the pitch angle will follow, but it would be a gradual process - you're unlikely to find yourself in even a shallow descent if corrective action is taken in a timely manner.
The fbw can take over and we need to be able, firstly, to detect that normal law is no longer desirable and secondly to revert to a safe control law.
I'm a little fuzzy on what "taking over" constitutes - Alpha Prot should not command significantly opposite the input it is given as that is not the way it is designed to work.
I'm all for waiting to see the incident report before making sweeping judgements. I find the fact that Alpha Floor is not mentioned interesting, as I would have expected it to have been activated if there was a manual pitch-up command given in that circumstance. Equally intriguing is the fact that the crew managed to correctly troubleshoot the situation and return the aircraft safely to the ground despite having no forewarning of the problem. Someone out to bash Airbus at any opportunity probably won't care about such questions, but if we're being open-minded about things it should definitely give pause for thought.
@jcj - No-one's talking about the Airbus ADR procedure being a permanent solution - it is clearly presented by the EAD bulletin as a temporary workaround while the AD is being implemented on the affected airframes.