Event Description
While in cruise flight, the pilot heard a loud clank and observed the oil filler door on the nose cowl pop open. Immediately thereafter, the engine lost a significant amount of power, and the windshield became covered with a film of oil. The pilot elected to make an emergency landing on a nearby road. Although the initial touchdown was successful, the oil-coated windshield impaired the pilot's ability to see, causing the aircraft to depart the side of the road and impact a culvert. The nose wheel strut collapsed during the impact.
Investigation Findings
Examination of the engine revealed that the number five connecting rod cap bolt failed in overload after its retaining nut backed off to a point where it was retained by only two threads. Further examination of the nut and cotter pin disclosed that the cotter pin, which retained the rod bolt nut, had experienced fatigue crack propagation failure in two locations. It was determined that both cracks initiated at locations where the insufficiently torqued connecting rod cap bolt nut had vibrated against the cotter pin surface.
Conclusion
The loss of engine power and subsequent forced landing were due to mechanical failures within the engine assembly. The event underscores the importance of proper torque and secure fastening in connecting rod components.