On August 14, 1999, an Aeronca 11AC (registration N3184E) was involved in an aviation accident near Rockwall, TX. Investigators recorded the probable cause as: The mechanic's improper machining of the crankshaft during a major overhaul, which resulted in a fatigue crack and subsequent failure of the crankshaft. A factor was the lack of suitable terrain for the forced landing. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
While maneuvering in the traffic pattern, a private pilot experienced total engine power loss and landed in a field of 5-foot maize. Examination revealed a fatigue crack in the crankshaft at a secondary radius containing machining marks. The crankshaft had been ground 0.010 inches during a previous overhaul.
Accident Summary
While maneuvering in the traffic pattern, the airplane experienced a total loss of engine power. The private pilot elected to land in a field that contained 5-foot-tall maize crops.
Engine Examination
Examination of the Continental A-75-8 engine revealed that the crankshaft was separated aft of the #3 connecting rod journal. Further examination of the crankshaft fracture showed that a fatigue crack had developed in a secondary radius between the journal and the cheek. The secondary radius contained machining marks.
Maintenance History
The engine's maintenance records indicated that during the last major overhaul, the crankshaft had been ground 0.010 inches.