What happened
A flight instructor and a student were traveling back to their home base following landing practice at a local airport. When the aircraft was approximately eight miles from its destination, the engine began running roughly. During this period, the propeller became unattached from the engine, causing the engine to stop running completely. The crew performed a forced landing in a field, and there were no injuries resulting from the incident.
The investigation
Post-accident examination of the aircraft revealed that the crankshaft had suffered a complete fracture. Further inspection of the crankshaft identified a fatigue failure that originated from an oil transfer tube hole. This specific hole was found to have an enlarged diameter portion that exceeded the specified value. Additionally, a review of the airplane's logbook indicated that the aircraft had been involved in a propeller strike four years and 1,220 flight hours prior to this accident.