Originally Posted by
DaveReidUK
There have been a number of 707/720 accidents where the THS has been implicated, including a fractured jackscrew, a stalled actuator and a trim motor failure, but I'm not aware of any that involved a working stabilizer jackscrew being backdriven by airloads.
Not of course directly (or even necessarily) implicated, but can anyone explain Item 4 on the Runaway Stab memory item list quoted below. How is that the Stab could continue "uncommanded" movement after the two cutout switches are flipped? What is it that those switches do or don't do? Is the QRF allowing for some purely mechanical "uncommanded trim" that can only be mechanically countered with the wheel (assuming noting's catastrophically broken...)?
If the Runaway Continues
3 STAB TRIM CUTOUT SWITCHES (both) - CUTOUT
If the Runaway Continues
4 STABILIZER TRIM WHEEL - GRASP and HOLD