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 essential to identify issues like fouled spark plugs (indicated by an excessive RPM drop) or improper magneto timing, ensuring the engine's ignition system functions safely on each magneto.
- A "hot mag" condition, where a magneto fails to ground (no RPM drop or engine running when ignition is off), is a critical safety hazard preventing proper engine shutdown and risking unintended engine starts.
- Proper leaning during ground operations helps prevent spark plug fouling, and performing a grounding check at shutdown is crucial to confirm both magnetos are truly off, preventing accidental propeller-related engine starts.
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