What happened
While performing a base leg approach to the airport, the aircraft experienced a sudden loss of engine power. The pilot was unable to reach the runway and instead performed a forced landing into a swampy area located short of the landing strip. There were no fatalities reported in the accident.
The investigation
A mechanical examination of the engine focused on the accessory section, where investigators discovered that the idler gear assembly had been displaced. This component is responsible for transferring power from the crankshaft to the camshaft and the left magneto. The investigation found that the mounting shaft had also been displaced, resulting in an elongated shaft hole.
Further inspection revealed significant damage to the hardware: the upper portions of both shaft mounting plate retaining screws were missing. One lower screw appeared to have sheared, while the remaining portion of the upper screw showed signs of mechanical damage. Additionally, the crankcase surface area surrounding the upper screw hole exhibited fretting, and the idler gear itself had several missing and damaged teeth. Remnants of the shaft mounting plate retaining screws and the screw lockplate were recovered from the bottom of the crankcase.
Findings
The engine's operating time was below the recommended time between overhaul (TBO). However, the manufacturer's guidelines also recommend an overhaul if the TBO is not reached within 12 years; this specific engine had not been overhauled in over 30 years. While the engine was significantly overdue for maintenance based on age, investigators could not definitively correlate the lack of overhaul to the displacement of the idler gear assembly, and the exact failure sequence remained undetermined.