[rurban]

That cannot be. It was widely reported that the complete South Western Airlines MAX fleet insisted on the second sensor being installed. And so they did. They bypassed the FAA rubber-stamp approval. The FAA not knowing about this is not plausible. Everybody knew that. It was a major criticism on the FAA ability to control air safety.

[rainbowzootsuit]

Are you speaking of the AOA disagree "light" here?

I use scare quotes above because it's not even a light, but instead an icon on the main console display.

Two AOA sensors exist on all of the original 737MAX aircraft. The original MCAS would use one sensor at a time for its calculation in an alternating fashion, which would swap between flights.

The AOA disagree was only an indication for the pilots and wasn't an actual upgrade to the function of the original MCAS for those that paid for the icon.

Juan Brown of the youtube channel blancolirio has given really excellent coverage if you look back through his explainations.

https://www.youtube.com/channel/UCphqjYZxxzjNbONVmY-0J7Q

[rurban]

Ah thanks, that was it, yes. They had two sensors, and just switched between them. The South-western upgrade was only an indicator for sensor failure, not a real input into the MCAS controller logic, as it should be.