Incident Overview
According to the pilot, while performing an engine runup, the right magneto drop was found to be significant. When the magneto switch was returned to the "both" position, the engine operated normally. However, upon retesting the right magneto, the engine backfired and ceased operation. The pilot restarted the engine, but the same RPM drop on the right magneto persisted. Puffs of smoke were observed emanating from beneath the engine.
Discovery of Fire
The pilot exited the aircraft and opened the cowling, at which point he saw flames. The local fire department responded and extinguished the fire.
FAA Inspection Findings
An FAA inspector examined the aircraft and determined that the fire originated from the alternator. The instrument panel sustained burn damage, but the interior side of the firewall remained unburned. Additionally, a short appeared to have occurred at the top of the instrument panel.
Conclusion
The investigation confirmed the presence of a short circuit at the top of the instrument panel and identified the alternator as the source of the fire. No further causal factors were specified in the source.