Originally Posted by
tdracer
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).
Although in the past they did pull c/b’s .