Interesting.
EMERGENCY AIRWORTHINESS DIRECTIVE 2014-0266-E_1 NOVEMBER 2014
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.
This is not only interesting, but essential, but only if the lower part of that EAD is mentioned:
To address this unsafe condition, Airbus has developed a specific AFM procedure, which has been published in AFM TR 502. For the reasons describe above, this AD requires amendment of the applicable AFM to advise the flightcrew of the emergency procedures for abnormal Alpha Prot.
Although it's early, most contributors would speculate (it's a rumour forum) in some sort of upset scenario in conjunction with CB or icing. So now the multi million question is:
- Were the pilots aware of and trained in this emergency directive?
Another question to ask yourself: Re-read the directive carefully and ask yourself if you would step into your car, if a similar chilling warning about its driving characteristics would be issued.
I guess not! You would rather leave it in the garage and sue the manufacturer.
It begs the question how any public transport machine gets the absolution by the regulators with such emergency directives, especially in regions perfectly prone to such weather phenomena.