Re. the two trim switches - not really to prevent trim RUNAWAY, but to prevent inadvertent trim operation. One of each pair of switches is an ARMING switch and the other is the DIRECTION selector. Therefore, in order to activate any trim, BOTH switches have to be operated. An interesting party trick is to operate the trim switches in opposite directions ... Q? What will happen?
A. the trim operates in the sense commanded by the DIRECTION switch, since the ARMING switch works the same in either sense.