Another item to think about with runaway trim is if it happens when the autopilot is engaged and you can not tell it is running until the autopilot gives up and disengages.  This was an issue on the 757 which had to be addressed by training.  If the trim starts running while the autopilot is engaged, all you get is a yellow EICAS message that says unscheduled trim and a tone.  If you let it run to the stops the autopilot will disconnect when the servos reach their force limit.  Then the aircraft will go into an unrecoverable dive or climb with stick forces well over 100 pounds.  Since the trim on transport category aircraft moves the whole stabilizer and the yoke only moves the servo tab on the elevator, which fly’s the elevator, the trim could easily overcome the control capability of the elevator.  Due to this, training was changed, that as soon as you saw the unscheduled trim message, to immediately reach down and disconnect both stab trims, which were under 2 guarded red switches next to the throttles.  I used to teach the 757 at northwest airlines and NWA does not use but a few memory items.  If an engine fails, catches on fire or systems fail, you simply continue to fly the aircraft and pull out the checklist when at a safe altitude.  The top of the emergency checklist says in bold letters, fly the aircraft, determine emergency, cancel the warning and do not hurry.  An unscheduled trim and explosive decompression are the only memory items where you react before pulling out the checklist.  That shows the level of importance the airlines place on this problem.  This does not directly apply to small aircraft but something to think about as far as when the autopilot is engaged.  This would be another reason why the 2 switch method is probably the safest or the safety trim system.  Testing your own aircraft to see if you can fly with full trim is another good exercise to attempt with a flight instructor.  Would not want to attempt this by yourself for the first time.

Luke Alcorn