Originally Posted by
MechEngr
The pilots could over-rule MCAS at any time. Press the trim switch on the wheel and MCAS trim command stops. That's clearly seen in the FDR graphs. The pilots retained the ability to set whatever trim status they wanted at any time. The source of the problem is the SMYD with a side of ADIRU - their design to pass on false AoA and a false stall warning is the source of the problem. As I mentioned even the Autopilot was trying to force the nose down when the ET302 crew got it to engage. Forcing the nose down on a stall warning is the action pilots should take (though they should actually set pitch and power appropriate for the weight and altitude.)
They changed the switches because (AFIAK) the NG guidance was that for any trim runaway, both switches are to be used, so operationally it made no difference.
The first Lion Air crew flew just fine with the manual trim wheel. It went so fine, they re-enabled electric trim, MCAS gave another kick, and they turned it back off.
If you are looking for the regulatory smoking gun, that was fired a long time before MAX was a twinkle in anyone's eye when they allowed a false stall warning to be acceptable and did not seek a way to invalidate a failed AoA sensor, perhaps as detected by loss of continuity in the de-ice circuit which occurs when the external vane is stripped from the plane.
Not sure if your writing is to "defend" the Boeing statements that "just switching off the electrical trim" using the trim cut-out switches is suitable to control the aircraft, but just reading your "instructions" makes me wondering, how pilots should be able to find out the need to do so, within seconds the cacophony started and let alone decide which actions to perform.
Not to say, IF the instruction to apply manual trim every 10 seconds, during the remainder of the flight, in case of an AoA sensor failure, to avoid an imminent crash, would have made it to the memorized instruction list, the whole MCAS disaster would have been unfolded before the first 737MAX take-off and MCAS design returned to the drawing board.