Plain English Meaning

A quick check before shutting down to make sure the ignition switch actually turns the engine's spark off. The pilot flicks the switch to OFF for a moment; if the engine keeps running normally, something is wrong and the propeller could still spark to life even with the key off.

Full Definition

A shutdown check in which the ignition switch is briefly moved from BOTH to OFF and back to BOTH while the engine is idling, to verify that both magnetos are properly grounded by the switch. If the engine continues to run smoothly with the switch in OFF, one or both magnetos are not grounding, meaning the engine could fire if the propeller is moved by hand even with the switch off.

Context Anchor

Performed during the , after the is parked and the engine is at .