Airbus Alpha Protection
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Airbus Alpha Protection
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.
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.
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.)
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.)
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.
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A red OEB was re issued for this problem around a month or so ago following an inflight upset on a lufthansa A321 near Bilbao. This was distributed to all bus operators worldwide so one would hope that this was not the cause of the QX flight. However it is up to the airlines to pass this info on to their line pilots. However as this problem had occurred a couple of years back, one would have hoped that faced with the situation they would know what to do.
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Apologies all round; research, which should have been done earlier, reveals an earlier pprune Tech Log thread
However, reading that, and a lot of other stuff, does little to confirm my already wobbly faith in FBW!
However, reading that, and a lot of other stuff, does little to confirm my already wobbly faith in FBW!
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And someone has just launched the same discussion, again, in Tech Log.
I must say it does seem odd that the Airbuses have been flying for all this time, evidently, with an FBW system that in certain - extreme but possible - circumstances would push the nose down further and further with no way for the pilot to regain control unless he/she knew the fix of turning off 2 ADRs, which has only recently been promulgated.
But I suspect that's an over-simplification.
I must say it does seem odd that the Airbuses have been flying for all this time, evidently, with an FBW system that in certain - extreme but possible - circumstances would push the nose down further and further with no way for the pilot to regain control unless he/she knew the fix of turning off 2 ADRs, which has only recently been promulgated.
But I suspect that's an over-simplification.
