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 critical for safety, indicating issues like fouled spark plugs (via excessive RPM drop) or improper magneto timing.
- A "hot magneto" (no RPM drop when selected) signifies a failure to ground, posing a severe hazard as the magneto continues to fire, making engine shutdown or propeller handling unsafe.
- Performing a magneto grounding check at shutdown is essential to confirm both magnetos are fully de-energized, preventing accidental engine starts, even after mixture cut-off.
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