Event Summary
While approaching the destination airport, the aircraft experienced a total loss of engine power. The pilot executed a forced landing on rough terrain, and the airplane nosed over approximately 200 yards short of the runway threshold.
Engine Examination
An examination of the engine revealed that its single drive dual Bendix magneto had internally failed. The magneto had accumulated about 4,309 hours of total operation and was 14 years old. No log book evidence indicated that the magneto had ever been overhauled. The internal inspection showed that the bearing stack around the rotating magnet shaft was devoid of lubrication, and the bearings did not rotate freely. The breaker cam was bluish in color and coked with cam follower material. The cam followers had decreased in size to the point that the points did not open.
Maintenance History
The engine had been operated for 2,184 hours since its last overhaul in 1984. The operator had performed the last two inspections but had not complied with Bendix's suggested four-year magneto overhaul schedule, which is published in FAA and Bendix bulletins. The operator stated that he only obtained bulletins when they were adopted by regulation into airworthiness directives. Bendix reported that bearing lubricants deteriorate beyond their useful life in four years.