Originally Posted by
Loose rivets
Again, one of the main bee-in-my-bonet's issues. Just what is the truth about that second (underfloor) column switch? I know, it's the third time I've shouted that question.
The column cutout switch operates just as it does on the 737NG, stopping opposite automatic trim movement if the column is more than a certain amount away from the neutral position, EXCEPT when the MCAS activation command occurs. MCAS activation causes temporary bypass of the column cutout switch via an added relay. This was necessary because the flight condition for which MCAS was the "solution" is a aft CG flaps up turn in which the crew is pulling the column far enough to approach a turning stall. In this condition, the unmodified column force characteristics did not meet the requirement in 14 CFR 25.203(a) to have increasing force required to generate increased pitch. MCAS was added to use a trim change to cause more column force to be needed to continue to pitch up in this condition.