Stab Trim Override switch is used to
override the control column activated stabilizer trim cutout switches.
These cutout switches at the base of the control column cutout electric stabilizer trim when the direction of trimming is opposite to the direction of control column movement . For example, you are exerting force and pulling the control column backwards but using the electric trim to trim forward at the same time. The control column cutout switch will not allow electric stabilizer trim in this case. That's when you use the Override switch and force the electric trim to work and the best example of this is a Jammed elevator situation and the NNC directs us thus.
Hope this explains it .
masalama
