Originally Posted by
paulross
SLF non-aviation engineer here. I'm curious, how relevant would the behaviour of an A-340 be to the accident flight that was with an A-330? I know the FBW and cockpit is the same between the two types, but the actual aircraft aerodynamics and behaviour, is that 'similar enough'? Or is it just that Airbus did not have an A-330 with and evacuation system and thought that they could learn something useful from the A-340?
very similar. the event wasn't related to a thrust couple/THS mismatch, this was purely a transient instrumentation and degradation of control laws that should have been a yawn, but the response was random in the face of utter SA loss. Loss of ADC data is not unheard of event, and yet crews get started sideways with it quite rapidly. An Airbus FBW is actually an elegant system, it is really nice when working, crosswinds are still a bit awkward, but the bit that makes them nicer when working normally results in guys n girls often having issues when degraded control laws apply, the main thing being the missing dog to bite the pilot if they don't remember to use manual trim. The addition of the
U bit to the
C* law keeps the pilot in contact with the trim condition of the plane... (MCAS excepted, a plane with limited SAS functionality, and "FBW" being braided steel cables mainly) A330 and A340 are common architecture, there is negligible change, and aerodynamically, an AF447 type input on the 340 would have resulted in an AF 447 splash in an A340 too. Come to think of it, holding full back stick in a B727 will end up the same way, it did many years ago.
I cannot recall any aircraft that will allow a full backstick input without relief, that won't result in a headline, well, maybe the Ercoup, that had some curious limitations of control authorities.