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 use dual magnetos for ignition, providing redundancy and a slight power boost, and pilots perform pre-flight magneto checks during the run-up to assess their function by observing RPM drops.
Normal magneto checks show a specified RPM drop (e.g., max 150 RPM, 50 RPM difference), while anomalies like no RPM drop (indicating a P-lead failure) or an excessive/rough drop (often a fouled spark plug) require attention.
Issues like fouled spark plugs can sometimes be "burned off" by leaning the mixture at higher RPM, and advanced diagnostics using airborne checks or engine monitors (EGT/CHT) can help identify specific cylinder or ignition problems.

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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.