this is copied from the 'other ' forum, call it what you like. Sometimes s&*t happens and an opto kill is essential...........

"A run away 50cc just happen yesterday at our field. With no way to kill the engine the owner had to chase the plane around the field trying to catch it. It would have been funny if not for the fact that we all had to hide behind our car incase it came into the pits. Cause of problem: throttle servo linkage came off."