Incident Overview
During a climb through 3,500 feet, the pilot of a single-engine airplane heard a loud "bang" from the engine compartment. The engine subsequently lost power, and oil began leaking from the area. The pilot executed a forced landing on the Massachusetts Turnpike. During the landing flare, the aircraft struck highway reflectors, a sign, and an automobile. The extent of damage to the airplane and the automobile was not specified.
Engine Examination
Post-accident examination of the Lycoming O-360-A4M engine revealed a breach in the casing near the number 1 piston. The number 1 piston connecting rod cap was missing, along with one complete rod bolt and the manufactured head of the other rod bolt. The fracture surfaces of the missing components were obliterated, providing no clues as to the initiation of the fracture event.
Connecting Rod History
The engine had been overhauled using Type 74502 connecting rods. Since its certification in November 1974, the O-360-A4M engine had always been manufactured with LW-11750 connecting rods. Predecessor O-360 series engines were originally manufactured with 74502 connecting rods, but those rods and their immediate successors were superseded by LW-11750 connecting rods in May 1970. The LW-11750 rod features a larger grip area and uses a longer rod bolt to secure the cap to the yoke. However, the investigation found no evidence that the use of the 74502 connecting rod would have resulted in a rod or rod bolt failure.
Additional Notes
At the time of the accident, the engine had accumulated 50 hours since its last overhaul. No other contributing factors were identified in the source material.