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.
Plain English
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.
Context Anchor
Performed during the engine shutdown procedure, after the airplane is parked and the engine is at idle.
Derivation
Magneto comes from magnet, because a magneto uses magnets to make the electrical spark for the engine. Switch test simply means checking that the cockpit switch is actually controlling that spark as intended.
Why Pilots Care
Confirms the ignition system is functioning correctly before the engine is stopped, helping detect magneto issues that could affect flight safety.
Grounding Statement
When the switch is turned OFF during this test, the engine should stop receiving spark.
Intuition Check
Do not confuse the magneto switch test with the run-up magneto check. The run-up check compares how the engine runs on each magneto; the magneto switch test checks whether the ignition switch can actually shut the spark off.
Example Sentence 1
After taxiing in, the pilot performed the magneto switch test at idle and confirmed the engine momentarily died when the key was moved to OFF.
Example Sentence 2
If no RPM drop occurs during the magneto switch test, it may indicate a faulty magneto that requires maintenance.