August 2007 Issue

The Other Grounding

Magnetos are relatively simple devices, with well-understood failure points. But pilots need to know what they’re telling us when we check them.

Those of us flying aircraft with reciprocating engines should be performing what is commonly referred to as a mag check, or magneto check, prior to every flight. During the engine run-up, we turn the ignition key to the Left position to disengage or ground the right magneto, noting the rpm change, before turning the key back to Both. We then repeat this process by turning the key to Right to ground the left magneto. In addition to noting the rpm drop, if any, we also should be examining other instrument indications—fuel flow, if so equipped—and especially, the EGT values presented on a multi-probe engine monitor if one is installed.

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