https://leehamnews.com/wp-content/uploads/2019/04/Preliminary-Report-B737-800MAX-ET-AVJ.pdfWhat I find very curious in this preliminary report:
There are a couple instances where the report states the duration of the MCAS trim adjustments in seconds and in units.
But there are NO instances, anywhere in this doc, were the duration of the pilots' manual power trim inputs are ever reported. The only thing that is reported is the corresponding movement of the stabilizer.
In addition:
At 05:40:41, approximately five seconds after the end of the ANU stabilizer motion, a third instance
of AND automatic trim command occurred without any corresponding motion of the stabilizer,
which is consistent with the stabilizer trim cutout switches were in the ‘’cutout’’ position
This statement suggests that
1. The data recorder doesn't know the position of the stab cutout switches
2. The data recorder doesn't know if/when the trim motors are actually powered or not; the conclusion is made based on the actual movement of the stabilizer.
So we can't know if the power trim was working, properly, in this plane under these conditions, from the info in this report. Either this info was omitted/withheld intentionally, or it was not recorded.
AFAIC, it is completely possible that the pilots did not make appropriate trim inputs under the conditions. It is also completely possible that they did, but the stabilizer did not make the corresponding change. It is further possible they grabbed the trim wheel and successfully stopped the wheel from turning further down... but the stabilizer/jackscrew moved, anyway. Pulling back on the yoke puts a high force that wants to push the entire stabilizer into a further nose down position (ref Alaska Air 261)*. AFAIC, this mechanism is probably belt driven, and at some point belts slip. Gears or chains are possible, but not likely, IMO (and a snapped jackscrew or chain is also no good). There is potentially a point where cutting stab trim is the only way to prevent the MCAS from moving the trim further down despite grabbing the wheel, physically.... and that there is no way to move the trim back up without doing a roller coaster maneuver.
*I picture the stabilizer rotating around an axle that is near its midpoint. As long as the elevator is neutral, it doesn't matter what load is on the stabilizer; it can still rotate freely under power or manual trim. But an extreme elevator position can put enough torque that the stabilizer cannot be rotated against this force, anymore... though it might still be possible that the motor (MCAS) could turn the stabilizer in the other direction.