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. 288
The Other Grounding
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.
Key Takeaways:
- Pre-flight magneto checks are crucial for pilots to ensure the engine can run effectively on each magneto independently, with a normal RPM drop indicating proper grounding and function.
- An excessive RPM drop during a mag check can signal issues like fouled spark plugs (often resolvable by leaning the mixture) or improper magneto timing, requiring attention.
- A "hot mag" (no RPM drop) indicates a dangerous grounding failure, meaning the magneto remains active even when switched off, posing a risk of the engine not shutting down or accidentally starting.
- Performing a magneto grounding check at engine shutdown is essential to confirm both magnetos are truly disengaged, preventing inadvertent engine starts when the propeller is moved by hand.
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