Incident Overview
During the initial swath run, the propeller separated from the engine. The pilot executed a forced landing in a plowed field. During the landing, one main landing gear was sheared off, and the aircraft subsequently went through a barbed wire fence.
Inspection Findings
Following the incident, the #4 cylinder was removed to inspect the vibration damper pins in accordance with Airworthiness Directive (AD) 82-23-04. The trailing pin on the rear vibration damper exhibited considerable wear. The wear had progressed to the extent that the damper had been displaced from its normal position, causing interference with the skirts of the #2 and #3 pistons.
Additionally, minor wear was observed on the leading pin. The source states that this wear, together with the minor wear on the leading pin, caused vibration and subsequent propeller separation.
Subsequent Airworthiness Directive
Two days after the accident, AD 83-15-06 was issued, grounding all aircraft with the propeller-engine combination that was installed on this aircraft.