LAX04FA042 · Cessna 177RG

During cruise flight over mountainous terrain, a loss of engine power occurred and the airplane impacted trees during the subsequent forced landing attempt. The pilot radioed air traffic control personnel that the engine was losing power and would not sustain flight. He was attempting to make it to an airport when the airplane impacted trees in mountainous terrain. An airframe inspection was conducted with no discrepancies noted that would have precluded normal operation. The engine was equipped with a single-drive dual magneto that remained secure at its mounting pad. During manual rotation of the crankshaft, investigators could hear the "snapping" of the coupling, but no spark was observed at any of the leads. Magneto-to-engine timing could not be established because the contacts were not breaking electrical continuity. A functional check by the magneto manufacturer revealed that both magneto primary circuits had short-circuited to ground in all magnet positions, which was consistent with the breaker points not opening. Disassembly revealed that the plastic cam followers were melted and smeared in the direction of normal cam rotation. The breaker cams, made of sintered iron material, are supposed to be impregnated with oil per the service manual or production instructions for lubrication purposes at each overhaul. The oil lubricates the surface of the breaker cams over the cams service life. Four months prior to the accident the single-drive dual magneto had been removed, and the mechanic at a local fixed based operator had internally timed the magneto, then had completed a ground run and full operational check. The accident flight occurred 38.2 hours after this maintenance operation. According to the manufacturer, to internally time the magneto, maintenance personnel have to partially disassemble the magneto and physically touch the cam and breaker points. In accordance with the Service Support Manual instructions for the magneto, during this process the breaker cams and contact points should be inspected for lubrication, wear, burning, or melting. The on-scene examination revealed that the pilot was not wearing his shoulder harness, which remained stowed in the stowage sheath above the pilot's cabin door. The airframe manufacturer indicated that the airplane had been delivered new in 1975 with shoulder harnesses as standard equipment for the pilot and co-pilot. The coroner listed the cause of death as blunt force craniocerebral trauma due to an airplane crash.

Verbatim NTSB analysis and probable cause from the NTSB dataset