Stinson 108-3 N909C accident near Coleman, Michigan

Probable cause

The pilot’s improper installation of the generator drive gear, which resulted in a total loss of engine power.

NTSB analysis

The pilot had been flying for about 45 minutes when the airplane experienced a total loss of engine power. The pilot performed a forced landing onto a field. The airplane nosed over and sustained substantial damage to the fuselage and empennage.

Postaccident examination of the engine revealed that the single generator drive gear for the ignition system had separated into several pieces. The drive gear shaft installation called for a castellated nut with a cotter pin to retain the drive gear, but the cotter pin had not been installed and allowed the nut to back off, which ceased ignition to the engine. The generator was installed by the pilot, who did not hold a mechanic certificate, during his overhaul of the engine. The pilot stated that he performed the overhaul of the engine and installation of the generator under the supervision of a mechanic with an airframe and powerplant ratings. No other mechanical anomalies with the engine were noted.

Text from the NTSB. Open the NTSB docket for CEN20LA377 for the full record.