MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures

[fdr]

Originally Posted by DaveReidUK

Are you saying that the "roller-coaster" technique works by reducing airspeed significantly to the point where manual trim wheel forces are manageable where they weren't previously ?

There are two conditions where the manual trim force is reduced,

1. When the aircraft is at the speed (AOA) as trimmed by the THS/Stab, where no deflection of the elevator is needed
2. Approaching zero airspeed where the resultant force from the THS/Stab is reduced, being dependent on V.CL(stab-aoa)

Whenever the speed is considerable and the trim solution is not correct for the actual speed, then there is a need for a balancing force from the elevators. It is the elevator deflection that results in the excessive force on the stab screw jack which then may defeat the torque available from the pilot in manual application of trim.