Originally Posted by
FCeng84
The switch involved is the same one that interrupts pilot electric pitch trim if opposite the column displacement direction. I believe this interrupt is also active on the ground. When positioning the stabilizer for takeoff using wheel mounted thumb switch try moving the column in the opposite direction at the same time to see how far it has to be out of detent before stabilizer motion stops even though thumb switch remains activated. A note of caution that thumb switch input in opposition to column such that the column cutout activates if held for very long may trip a monitor designed to detect persistent contradictory column and trim commands. That might take some explaining. I apologize that I don't know the details on such monitoring (in particular how long the condition must persist before said monitor trips). I'm sure there must be some 737 savvy PPRUNErs out there who know and by the amount of traffic on this thread they are probably monitoring.
It works on ground. I have seen this when the wind push the yoke forward and I want to set takeoff trim. I need to pull the yoke back before I can engage the trim.
With STS it will continue to trim up even if I need to apply quite a lot of forward pressure to keep the nose from rising. I thing the parameters for the trim cut out to function are very high. Or possibly it doesn’t stop STS from operating.