Originally Posted by
infrequentflyer789
I agree that getting to 10^-7 seems a stretch, maybe I'm missing something though.
Well for a major criticality they only needed 10E-5 for uncommanded trim AND.
Recalling that even full AND stab trim can be overcome by the elevator normally, then uncommanded trim is not catastrophic.
But that ignores the elevator blow down effect. What was the likelihood of uncommented MCAS trim at speeds where blow down reduces elevator authority?
What is the likelihood of blowdown at all? Is it outside approved speeds?
I didn't see anything that suggested Boeing got the failure rate of the AoA input grossly wrong.
The NTSB did see the analysis that was done. We won't ever see it.
But the NTSB only faulted some of the assumptions, not the analysis with those assumptions.
Like assumptions about pilots recognizing and acting on the uncommanded trim w/o consideration of all the secondary effects of a failure.
Like all the disparate alarms and warning the AoA failure caused that hampered recognition and reaction to the uncommanded trim.