What happened
During flight maneuvers, the engine failed, necessitating a forced landing in a field. The impact of the landing caused damage to the aircraft.
The investigation
An examination of the engine revealed that the connecting rod cap for the number 5 cylinder had separated. Investigators found that one of the two bolts (bolt No. 1) failed due to an overload. Because the second bolt (bolt No. 2) was too damaged to analyze, the specific reason for its failure could not be determined.
Upon inspecting bolt No. 1, investigators observed signatures along its length. To facilitate a comparison, an undamaged rod was removed and an end cap was installed. Comparing the signatures on bolt No. 1 with the removed rod revealed that the bolt was loose and the nut had backed off by approximately 1/2 inch.
Review of the engine logbook showed the engine had been overhauled on September 3, 1980, at which time the rod bolts and nuts were replaced. At the time of the accident, the engine had accumulated approximately 654 hours of operation since that overhaul.