Accident Sequence
During cruise at 6,500 feet, oil appeared on the windscreen, severely limiting forward visibility. The pilot then felt severe vibrations and decided to secure the engine. A forced landing was executed, but the aircraft struck a small tree and subsequently encountered uneven terrain, resulting in damage.
Investigation Findings
The investigation discovered that a 90-degree aluminum fitting on the propeller governor oil line had failed at the point where it entered the engine case. The oil line itself was made of stainless steel and was designed to be restrained by clamps; however, those clamps were not in place.
Maintenance and Service History
A service instruction issued in 1986 recommended upgrading aluminum fittings to stainless steel. A service bulletin dated September 8, 1989, addressed numerous "engine failures due to oil starvation resulting from broken governor lines." According to the bulletin, the failure to reinstall the governor line clamps after maintenance had been the cause of numerous engine failures. Maintenance personnel had performed a top overhaul and an annual inspection, 50 and 12 flight hours respectively, prior to the accident.