Originally Posted by symbian simian

Lots of incorrect info here:

MCAS was initially put on the 737 for high speed cornering. When it became apparent the elevator pull became too light towards higher AOA at higher AOA it was decided to implement it for low speed too. This required the increased input to 2.5deg, and the FAA was never informed of this. Also the MAX would not pass certification without MCAS or some other fix, difference training has nothing to do with it.

MCAS was in the manual, Boeing asked the FAA for permission (and this was granted) to take it out to avoid giving pilots "too much information".

MCAS is always connected to both AOA indicators, it switches between inputs after every flight/power cycle. The reason it doesn't use both, like the KC-46 (mil B767) is to avoid having to notify the pilot if it detected a miscompare.

The option is to have AOA displayed and have an AOA miscompare warning annunciation on the PFD. This miscompare warning has been inop since 2017, but Boeing didn't tell this to the operators, and planned to slide the fix in during a planned later software update.

I know we get the Cliff Notes, but what Boeing did is on a whole different level.