How can you turn the magneto off in an aircraft?

Turning the magneto off in an aircraft is accomplished by grounding the primary circuit. Magnetos are self-contained units that generate electrical energy to produce a spark for the ignition system, regardless of the aircraft's electrical system. Each magneto has a switch that, when positioned to the "Off" position, connects the primary circuit to ground. This effectively stops the spark from being produced, thereby shutting down the engine.

Considering the other methods: reducing the throttle to idle does not impact the operation of the magneto directly; rather, it alters engine performance. Disengaging the fuel pump may stop fuel from reaching the engine, but it won’t mitigate spark generation from the magneto. Likewise, removing the battery connection typically affects the electrical systems running off the battery, but does not influence the autonomous function of the magnetos. Thus, grounding the primary circuit is the definitive and effective way to turn the magneto off safely.