Magneto Checks: Here’s What You’re Monitoring and Why

Even if you’re just bored and want to see what happens, you can do them while airborne.

Joseph "Jeb" Burnside

Wednesday, October 01, 2025 at 08:00 AM ET

Verified

Edited By:

Travis Tingle

Magneto checks aren’t just for run-ups necessarily. [Credit: Aviation Safety magazine]

Key Takeaways:

Aircraft engines utilize dual magnetos for ignition redundancy, and pilots perform pre-flight run-up checks to assess their function by observing RPM drops on each magneto.
Normal magneto checks involve an expected RPM drop within specified limits; significant anomalies like no RPM drop (indicating a P-lead failure) or excessive drop with rough running (often a fouled spark plug) require attention.
Pilots can attempt to clear fouled spark plugs by running the engine at higher RPM with a lean mixture; airborne magneto checks and engine monitoring systems offer more advanced diagnostics to pinpoint ignition system issues.

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A typical aircraft spark-ignition engine isn’t at all like the one powering the vehicle you drove to the airport. Unless, maybe, you drove a vintage tractor or motorcycle. There are so many differences, listing them here would take up lots of space, and we only want to focus on what pilots can do and learn about their magnetos from the cockpit.

As we should know from ground school, the magnetos use energy from the operating engine to create electricity. By rotating an armature near a magnet and then sending the resulting energy into a secondary coil, high-voltage electricity is created. The mags, in turn, are connected by a wiring harness to the spark plugs, usually two of which are in each cylinder.