Originally Posted by
das Uber Soldat
Airbus gave flight crew a heads up about erroneous sensor inputs causing uncommanded nose down inputs before QF72? News to me.
It's been a few years since I studied the QF72 official report in depth, but off memory, switching off any 2 of the 3 ADIRUs would have degraded the active flight law from Normal to Alternate - at which point flight envelope protections reverted to advisory only. If the QF72 crew had done this it would have prevented subsequent pitch-downs, but as the procedure wasn't prumulgated at the time it was deemed that the flight crew acted appropriately. It's my understanding that this procedure was subsequently prumulgated and boldfaced - primarily as a result of this incident.
FYI the issue wasn't caused by "erronious sensor inputs" - it was caused by one of the ADIRUs sending invalid outputs to valid sensor inputs, and it being accepted due to some incredibly unfortunate timing. Off memory there was a reasonably good case to argue that it was playing "mix and match" with data labling; specifically, labeling altitude data as AoA data, which the flight envelope protections subsequently acted on. Again, from memory, Airbus changed the AoA algorithm, made improvements to the BITE (Built In Test Equipment) and introduced the procedure to degrade the active flight law. May have been one more thing but I can't remember.
the only reason that 330 didn't spear into the ground precisely as the Max did was luck. At least the Max pilots had a memory item specifically designed to address the trim runaway in the 737. No such procedure in the 330 back in 2008, unless I"m mistaken?
The A330 has additional protections whenever the radar altimeters detect that it's within 500 feet of the ground, but I'm uncertain if these would have made any difference. The pitch down events were of incredibly short duration - but abrupt.
If anyone is interested, the official report gives a facinating insight into Airbus design philosophy and system detail - especially on the A330 (also applies to A340 I believe). The official report can be found here:
https://www.atsb.gov.au/publications...ir/ao-2008-070
I remember at the time counting about 7 "holes" in safety nets that just happened to line up; it was incredibly "unlucky" but - none-the-less - shouldn't have happened, but did. In a comparison study of the official report of a similar Boeing event that resulted in an uncommanded pitch-up I was left with the impression that whereas Airbus engineer in a gobsmacking amount of fault-tolerance, safety, and redundancy to the flight control systems, Boeing lagged somewhat behind; they too had redundancy & fault-tolerance, but by my observation, just not as much; and after their design decisions regarding MCAS on the MAX came to light it reinforced to me that they still have a long way to go to catch up.