Here's an extract from
an EASA EAD, issued 9th December, for A330 and A340 aircraft. Exactly the same words are used in an
EAD for A318, A319, A320 and A321.
An occurrence was reported where an Airbus A321 aeroplane encountered a blockage of two Angle Of Attack (AOA) probes during climb, leading to activation of the Alpha Protection (Alpha Prot) while the Mach number increased. The flight crew managed to regain full control and the flight landed uneventfully.
When Alpha Prot is activated due to blocked AOA probes, the flight control laws order a continuous nose down pitch rate that, in a worst case scenario, cannot be stopped with backward sidestick inputs, even in the full backward position. If the Mach number increases during a nose down order, the AOA value of the Alpha Prot will continue to decrease. As a result, the flight control laws will continue to order a nose down pitch rate, even if the speed is above minimum selectable speed, known as VLS.
This condition, if not corrected, could result in loss of control of the aeroplane. (My bold.)
Does this have any resonance whatsoever with the 2 cases of Airbus loss of control that we are all thinking about at the moment, specially the last one? What could cause "blocked AOA probes"? I don't even know what they look like on an Airbus, or how they work; could ice do it?
Probably not, but it crossed my mind when I read the EAD, and I'm curious. Not least at the way that seemingly it has only recently been discovered.
I've buried the question here, in the hope that someone knows the answer while avoiding the R&N hamster-wheel and FS experts.