Re:Boeing Built Deadly Assumptions into 737 Max, Blind to a ...
by cameldrv on Monday June 03, 2019 @12:27AM
(#20080412)
Having a safety system that rarely fails to prevent an accident is much different statistically than a safety system that rarely causes an accident.
Suppose the crash probability on a normal flight is 1/1E7, but without MCAS it's 100x more dangerous, or 1/1E5.
Suppose MCAS failure probability is 1/1E6, the probability of an additional crash due to the failure of MCAS is 1/1E11, which is acceptable.
The problem is that in practice, the crash probability if MCAS fails is empirically 2/3 instead of 1/1E5, because MCAS actually causes the crash rather than merely failing to prevent a crash.
Suppose the crash probability on a normal flight is 1/1E7, but without MCAS it's 100x more dangerous, or 1/1E5. Suppose MCAS failure probability is 1/1E6, the probability of an additional crash due to the failure of MCAS is 1/1E11, which is acceptable.
The problem is that in practice, the crash probability if MCAS fails is empirically 2/3 instead of 1/1E5, because MCAS actually causes the crash rather than merely failing to prevent a crash.