it looks like it will be pretty hard to exactly determine the cause...
Or... maybe not.
https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/Apologies if someone else has already linked this. It seems like it was published within the last 18 hours. It seems pretty clear, so far. It contains almost all the important details in this thread but without the faff.
1. FFA let Boeing approve its own plane, in some ways.
2. The MCAS was said to move the elevator only 0.6 degrees. But Boeing increased it to 2.5 degrees after test flights. No one told this to the FAA.
3. After the elevator is manually moved by the pilot, the MCAS can re-trigger. Doing a full 2.5 degrees again. (In the Ethiopian Airlines flight, the captain corrected the plane 21 times, then he handed the plane to the FO. The FO made only a tiny, partial correction after MCAS triggered. Then it triggered again. This put the elevator to full nose down, and the plane crashed shortly after.)
4. Boeing didn't include info about MCAS to its customers, at all.
5. MCAS was probably incorrectly classified. FFA approved the original classification based on 0.6 degrees of elevator adjustment. That changed to 2.5 (and was actually unlimited, due to retriggering). And even they way it was initially classified, it still needed to have two sensors, not just one.
6. They didn't consider the human factor of what happens to a pilot when 2.5 degrees of elevator adjustment is made out of the blue and repeatedly retriggers and no one told them this could even happen. 5 degrees is basically maximum nose dive; so I think "panic" might be on the menu. I wonder how many 737 commercial (not test) pilots have ever intentionally used even 2.5 degree downward angle on a flight.
So basically, this MCAS system, in the hands of a pilot who has spent 6,000 hours of flight time living by very small and gradual adjustments and essentially "not messing up", becomes a shoddy encoder wheel, where you manage to turn the volume up by 1, then it goes down by 10, then up by 1, then down by another 10. And then the music stops playing.