On March 7, 1989, a Stinson 108-2 (registration N150C) was involved in an aviation accident near Custer, SD. Investigators recorded the probable cause as: The pilot's installation of both magnetos without cotter pins on the drive gear retaining nuts, which allowed the nuts to back off, disconnecting the magnetos and allowing one gear to fall into the engine, resulting in engine stoppage. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A private pilot experienced engine failure during climb out after installing magnetos without cotter pins. Attempted landing on a gravel driveway resulted in gear collapse and slide.
Incident Details
A private pilot was performing a flight following the installation of two magnetos. According to a witness and the pilot, the engine quit during climb out. The pilot reported hearing something break inside the engine. Subsequently, the pilot attempted to land on a gravel driveway located south of the runway. Upon impact, the main landing gear collapsed. The airplane came to rest after sliding approximately 150 feet.
Post-Accident Findings
A post-accident inspection revealed that both magnetos had been installed without cotter pins on the drive gear retaining nuts. This omission allowed the nuts to back off during operation, which disconnected the magnetos. Additionally, one of the drive gears fell into the engine, leading to the reported engine stoppage.
Probable cause
The pilot's installation of both magnetos without cotter pins on the drive gear retaining nuts, which allowed the nuts to back off, disconnecting the magnetos and allowing one gear to fall into the engine, resulting in engine stoppage.