Incident Overview
A pilot was unable to start the engine and sought assistance from a mechanic. The mechanic diagnosed the issue as a problem with the ignition switch and proceeded to disconnect the P-leads. This action was based on the belief that it would keep the magnetos continuously "hot."
Maintenance Actions
With the P-leads disconnected, the design intended for the magnetos to be continually grounded via leaf spring connectors. However, despite this, the engine started successfully with the P-leads disconnected. No magneto check was performed before takeoff.
Engine Failure and Landing
After departure, the engine began to vibrate and misfire. The pilot attempted to return to the airport. During the attempt, the engine lost all power. The pilot executed a forced landing, which resulted in the landing gear collapsing as the aircraft came to rest short of the runway.
Post-Accident Examination
An examination of the engine revealed that with the P-leads disconnected, the right leaf spring connector effectively grounded the right magneto. However, the left magneto remained ungrounded for a period. Evidence of arcing was found between the left leaf spring connector and the magneto case. Additionally, the spark vibrator was found to be weak. No other pre-impact mechanical problems were identified.