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 utilize dual magnetos and spark plugs per cylinder for redundancy and increased power, with magnetos generating their own electricity.
Pilots perform a pre-flight magneto check during the run-up by individually grounding each magneto and monitoring RPM drop, with acceptable parameters typically under 150 RPM.
Anomalies during mag checks, such as engine quitting, no RPM drop, or rough running, indicate potential issues like P-lead failure or fouled spark plugs, requiring specific pilot responses or mechanic intervention.
Magneto checks can also be performed airborne, and multi-probe engine monitors can further assist in diagnosing specific cylinder or spark plug issues by analyzing EGT and CHT data.

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.