Originally posted by BOAC
The system 'knows' that the AoA of the 2 sensors is incorrect v IAS and weight. Supposedly it asks the crew to 'check the GW'. Maybe it does, maybe it doesn't; maybe they do, maybe they don't.
That highlights the Airbus philosophy in regard to the algorithims used to "protect" their aircraft. It clearly demonstrates that because 2 out of 3 AoA sensors polled provided the same values, "something else" must be wrong. Application of
Machinbird's Common Mode Rejection (CMR) method would have detected (eons earlier) that 2 AoA sensors already had invalid outputs, i.e. each sensor's output value failed to change with time. Demonstrating that the Alpha Protections principles around which the computed performance of the aircraft is based, are not infallible.
Yet strangely, as it had already been "polled out", the remaining AoA sensor provided the ultimate stall warning - something the "polled in" sensors were unable to do. Strange? Not really, as to me it reveals that irrespective of the AOA sensors polled status, they are all used in a logic OR sense so that either will provide a stall warning.
Now we come to the trim! This is a case where the crew hadn't thought through the "what ifs" should something go wrong at the Alpha(Prot) point of the flight. Airbus law change "memory item" - check THS position! Else, the following applies -
- If you want to go up, pull back on the yoke.
- If you want to go down, pull back a little more.
- If you want to go down real fast and spin around and around and around, just keep pulling back.
PJ2
Information overload is a modern "fact of life", and understandably the ability to filter out the non essential stuff is a must. We know the warnings given to the AF447 crew, 10 in the first tranche (probably within seconds) and not all of those were "essential". Sadly, when the recorders are recovered, we will most likely see a sequence of events not dissimilar to this XL misadventure.
Forewarned is forearmed.
mm43