Incident Overview
During maneuvering flight, the engine ceased operation, resulting in a forced landing in a field. The aircraft sustained damage during the landing.
Engine Examination
Following the incident, an examination of the engine was conducted. The investigation revealed that the No. 5 cylinder connecting rod cap had separated. One of the two bolts securing the cap, designated as Bolt No. 1, failed due to overload. The second bolt, designated as Bolt No. 2, sustained damage that prevented a determination of the reason for its failure.
Detailed Findings
Bolt No. 1 was examined and found to have signatures along its length. An undamaged connecting rod was removed from the engine, and the end cap was installed onto it. The signatures on Bolt No. 1 were compared with those on the removed rod. This comparison determined that Bolt No. 1 had been loose, and its nut had backed off approximately half an inch.
Review of Engine Logbook
A review of the engine logbook revealed that the engine had been overhauled on September 3, 1980. During the overhaul, the connecting rod bolts and nuts were replaced. At the time of the incident, the engine had accumulated approximately 654 hours since the overhaul.
Conclusion
Despite the examination, no determination could be made as to the reason for the loose connecting rod bolt assembly or the failure of Bolt No. 2.