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 spark-ignition engines rely on dual, self-contained magnetos for ignition redundancy, and pilots regularly perform pre-flight magneto checks during run-ups, monitoring RPM drops within specified limits (e.g., max 150 RPM drop, 50 RPM difference between mags) to assess system health.
Anomalies during magneto checks, such as an engine quitting on one mag, no RPM drop, or rough running with a large RPM drop, signal potential issues like P-lead failures or fouled spark plugs, requiring specific pilot actions (e.g., reducing power to prevent backfiring) or immediate mechanic intervention.
Beyond pre-flight, magneto checks can be performed in flight (especially at high power or lean of peak) for more effective diagnostics, with advanced engine monitors (EGT/CHT) providing crucial data to pinpoint specific cylinder or spark plug problems for maintenance.

See a mistake? Contact us.

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.