Software Won’t Fix Boeing’s ‘Faulty’ Airframe
The key failure of the MCAS system I have not seen discussed is that if it is overriden, and triggers again, it cranks the trim another notch. Trigger it five times, and each time it makes the plane less flyable. When Lion Air crashed, it had been triggered many times.Making MCAS pay attention to two sensors might help a bit, but the disaster is still latent. Once it trims, it should never trim again without a full reset back to baseline. There are standards relating to this sort of thing in flight assist, about how much "authority" an automated system may assert, in total, and they were ignored, apparently because they did not treat it as part of the autopilot system.If the standard had been observed, the bad sensor could not have had much effect on the flyability of the plane. The pilots would have needed to apply some force to keep the nose up, but would have succeeded, long enough to discover a fix or to turn around and land.