It is surprising to me that the details of the MCAS functionality have not come to full focus here within PPRUNE yet. MCAS inserts airplane nose down stabilizer as a function of Mach number and how far beyond a trigger AOA value (a function of flight condition) the airplane has gone. When AOA reduces to below the MCAS sctivation threshold MCAS runs the stabilizer airplane nose up the same amount so that it is back where it started. If the pilot commands manual electric trim while MCAS is active, MCAS is “reset” based on the assumption that the pilot has taken over responsibility for pitch trim and will bring the stabilizer to the proper trimmed position.
The only way to get MCAS to insert more than one increment of airplane nose down trim is for all of the following to occur:
1. High AOA is detected leading to one MCAS increment of stabilizer
2. Manual pilot electric trim command is detected thus causing a reset of MCAS
3. Pilot does not fully command stabilizer to its trimmed position
4. High AOA is once again detected leading to another MCAS increment of stabilizer