Most Gas engines use both a mechaical kill with access outside the fuse.
and a radio operated killswitch, Wiring of the switches depends on the
type of engine, electronic igntions you can just kill the power to the
ignition box, Magneto engines you can add a ground to the coil.

Like Ken said it is a definite safety issue, All fuel powered planes should have some
way to shut the engine from the transmitter.