Originally Posted by
Ranger One
First, that sentence doesn't make sense; if a signal is known to be "erroneous", surely MCAS shouldn't act at all?!
The thinking behind that is presumably that it is safer to assume that the higher of two differing AoA signals is the correct one and initiate a single-shot application of MCAS if the criteria are satisfied.
More significantly, my understanding is that MCAS was given the greater control authority because, when the system with the original intended control authority was tested, it was found to be inadequate and still produced handling characteristics that were not certifiable; Boeing had to significantly increase MCAS authority (without properly informing the FAA of the design change!) in order to get the high AoA handling certifiable. So how can they now reduce MCAS authority and retain certification?
It was the initial 0.6° nose-down trim application that wasn't certifiable. There's no indication in the Seattle Times article that Boeing are planning to revert to that.