Originally Posted by
alf5071h
Only when the flaps were retracted did the trim abnormality - MCAS failure, appear; without alerting, or prior knowledge of an unknown system.
Agree but for a couple of pedantic nitpicks: On ET I am pretty sure MCAS only appeared when autopilot disengaged (it was engaged for half a minute), which I think was after flaps up. Also, MCAS wasn't an unknown system at that point since it had been revealed in LionAir crash investigation, in fact if you look at e.g.
ACN: 1597380 it's clear that some pilots at the time (after LionAir crash) both knew about MCAS and briefed preventative actions against it. Unfortunately the preventative action was "engage AP".
Additionally the first pitch-down (or at least pitch reduction) for ET was under autopilot and therefore in theory not MCAS. It's not clear why AP got confused, dodgy AOA at a guess (but I don't think that has been confirmed anywhere), nor is it clear why it disengaged (although GPWS alert sounded shortly after...). There have been other reports of MAX AP unexplained pitching down shortly after takeoff (one is the ACN above), to my knowledge this (may not all be same issue) remains unexplained. Obviously the solution is disengage automatics and pull up, but then MCAS comes into play...