FSX, I'm well aware of the differences between fixed wing and rotary wing power plants and transmission systems. I stick by what I wrote. In the case of a piston engine overspeed, it's not excessive torque that would cause the damage to the engine itself. The service bulletin backs this up. Valve gear and piston rings do not get broken by over-torqueing, but by over-speeding. Balance shaft bushes are damaged by excessive inertial forces, not by torque.
If an over-torque occurred, it would result in a transmission or main rotor inspection, and that isn't the problem here.
As far as switching off the good mag of a helicopter piston engine in the case of the other being possibly faulty, no thankyou. I'm not in the habit of trying stuff likely to kill me, especially as this means the left hand was away from the collective to operate the magneto switch. I read that bulletin, too, btw. The difference is that a helicopter transmission has an over-run clutch / freewheel device and of course an aeroplane engine has the prop bolted directly on the crank (at least in most cases, there are some exceptions which are geared/belt driven). Yes, switching off the ignition would probably result in a sudden engine stoppage because nothing external would be driving the crankshaft round.
But that problem is about as far from an engine over-speed as one could get so I don't see the relevance...
