Originally Posted by
Loose rivets
TryingToLearn
Just a small nit-pick. MCAS didn't fail. At all times the software did exactly what it was written to do. The vane failures happened to parts that were at the time NOT designated in the 'Catastrophic' range. The final two failures of the vanes were cause by completely disparate mechanical issues. To be on that close timescale was a bizarre coincidence but one that may have caused a much more rapid and accurate set of investigations. Saying that two accidents being close together is a good thing becomes a rather unsavoury philosophic argument.
The design made one AoA sensor a
single point of failure in a system that had complete authority over elevator trim. In the event of that single AoA sensor failing in a particular situation, the only way to stop the plane flying into the ground was to disable automated elevator trim for reasons that were undocumented, and where the aircraft did not behave the same as in a "typical" runaway trim situation.
Several pilots did encounter this problem and recovered their aircraft, knowing nothing about why their automated trim went bats--t. Then two flight crews didn't.
There actually was a steady cadence of MCAS "failures." It's not that two incidents occurred together in time out of the blue. There were incidents on the timescale of every few weeks.
This design shouldn't have passed the laugh test let alone certification.
So I assert that MCAS
did fail.
And worked as designed. It was designed to fail.