Originally Posted by
A Squared
I don't know. I'm just saying that Boeing's words in the AD seems to indicate that moving the switches to "CUTOUT" is not a 100% guaranteed clean kill on stabilizer trimming. Why that is, or how it happens, I can only speculate. I have a hard time imagining designing a system that moves your flight control surfaces, and you can't turn off completely. Perhaps Boeing is alluding to the possibility that the contacts in a STAB TRIM switch become welded and don't open the circuit. I'm grasping at straws here.
There are several failures that can cause a stab trim runaway - and not all are solved by turning the system 'OFF". In addition to welded switch contacts, the motor can fail in such a way that you can't turn it off. These failures are rare, but not impossible - the only way to 100% disable the system is to pull the circuit breaker(s) (and that's not something they like to tell the pilots to do).