Originally Posted by
Dave Therhino
Yes, the pilot could keep counteracting the MCAS input with equal and opposite trim, and get into a trim cycle where, while the ride is wild, control is never lost until the electric trim is shut off or by flap selection for landing. Remember the MCAS function uses the high trim rate and can put in up to 2.5 degrees each cycle, so the pilot's trim inputs counteracting each cycle need to be fairly large. That is what the crew apparently successfully did in the flight prior to the Lion Air accident flight. Remember, by putting in opposite trim, the pilot interrupts the MCAS function and causes it to re-arm for another cycle, which will be triggered five seconds after trim switch release if the MCAS logic is still satisfied (manual flight, flaps up, same side AOA sensed beyond some threshold). However, if on repeated successive cycles of MCAS input, the pilot fails to fully reverse the amount of trim MCAS has put in, the nose down trim will continue to build until the column input can no longer override its effect. This can happen in just a few MCAS cycles.
Absurd design philosophy as I said before. A workaround of the worst sort... and naive in concept. Worse than a bodge* which can be seen for what it is !
* from Chiltern Beechwood Chairmakers (bodgers)