Originally Posted by
DaveReidUK
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.
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.
On the first point about AOA signal selection, picking the higher of two would get you into the same situation that was seen with Lion Air. A comparison monitor that disables MCAS would be much more robust and seems to be what rumors are suggesting. It may be that Boeing is also considering how the system would response to two sensors that track, but are both erroneously high. That may be where the suggestion of limiting the response to a single MCAS increment comes in.
On the second point, MCAS was originally thought to be needed only at high Mach number where 0.6 degrees is sufficient. The need for MCAS at lower Mach numbers was discovered later. The 2.5 degree MCAS authority is only at low Mach numbers with a schedule that ramps MCAS authority down to about the original design value of 0.6 degrees at high Mach numbers. From what we have heard I about the need for MCAS I doubt it will be sufficient to limit it to 0.6 degrees at all Mach numbers.