Originally Posted by extricate
I know the AOA sensors were iced up
You shouldn't be knowing this as they were not simply iced up. Bearings on 2 out of 3 AoA probes froze due to water ingress, consequently to pressure washing the a/c without protective covers fitted.
Why coudn't the PF control the aircraft? Due to flight law degredation? Can someone explain the mechanics here?
Flight control laws passed into direct and then abnormal alternate, both without autotrim. THS overpowered elevators per design. MAnual trim was not used.
I let the speed degrades to vPROT and when aPROT engages, i disconnect it purposely because I want to let the speed reduces to vMAX? Am I correct?
No. Idea was to test AlphaProt, disconnecting it would be pointless. Pulling the stick to stop will give you alpha max, it won't disconnect protection.
This is part of the stall test too right?
Wrong. It is not and no full stall was planned - for that FCS laws have to be deliberately degraded and this is not line pilots' stuff.
If the speed is reduced to vMAX, the aircraft will fly at vMAX
1. V
alphaMax 2. stick has to be held against the back stop 3. in normal law only.
why in this case, the speed continued to degrade? Due to loss of flight laws?
No. Protections are based on measured alpha, which bore no resemblance to actual one so prots weren't triggered. FCS law degradation occurred after the first stall.
Lastly, could the aircraft be saved even though if this flight was conducted at 3000ft?
If aeroplane had been washed properly, the crew would get away with improvised flight test.
What would you do differently?
I'd stop wondering about people so blissfully unaware of environmental and organizational factors affecting the pilot's decisions and actions that they come up here with simple question of "What would you do differently?".
This is what it looks like when I'm going easy.
Originally Posted by WeekendFlyer
unfortunately for the crew the AOA sensor failure caused the FCS to degrade from normal law to alternate
No. There was no unequivocal failure of any AoA probe right down to impact. Probes 1 and 2 send values that were false but stable and within normal range. Law degradation occurred as the aeroplane was tumbling following full aerodynamic stall.
This is an interesting case because it is another example of the Airbus low speed protection and FCS law mode changes occuring as designed, but the crew awareness and response being insufficient or counterproductive.
I find attempt to test stall protection at 3000 ft without knowing the speed at which it should go off more interesting.
To my mind it does beg the question as to whether the Airbus design strategy has some implicit human factors weaknesses when it comes to pitch control in low speed flight in conjunction with subtle failure modes leading to FCS law degradation.
To my mind this is just another half-informed, fully-opinionated, loaded question. Of course, I might be mistaken and there was never, ever case of loss of control at low speed with "conventional" controls.
Removing conventional feel from the primary flight controls was a design decision that Airbus and the certifying authorities were and still are content with
There is no plausible reason to change their minds. Besides, artificial feel is pretty complex beast with not much in common with conventional feel.
However, from the accident reports it does appear that removing the influence of conventional feel from flying controls is not necessarily a helpful thing in some circumstances, because on a conventional aircraft an out of trim condition can be felt through the force one is having to apply to flight the controls, particularly in the pitch axis.
If we don't read the accident reports where AFCS trimmed "conventional" aeroplane excessively and clueless crew failed to trim when she was suddenly handed back to them or where panicked pilots kept pulling and trimming into stall, well then, you are right.
it is highly unfortunate that the AOA probes failed in the way they did, leading to loss of stall protection.
Yeah, I'm superstitious too: I believe that not following procedures brings bad luck.