Accident Overview
While in cruise flight at 9,000 feet over the ocean, the pilot heard a loud bang emanating from the engine compartment. The windshield became covered with oil. The pilot reported that the engine produced partial power before both the engine and propeller stopped. The pilot subsequently ditched the airplane in the ocean.
Wreckage Examination
Examination of the wreckage revealed an 8-inch by 5-inch hole in the top of the engine case. The camshaft was exposed and completely fractured aft of the #3 intake lobe. The #4 connecting rod was fractured approximately at its midpoint. The upper half of the connecting rod remained attached to the piston pin, and the piston was staked in the cylinder. The lower half of the #4 connecting rod and its corresponding bearing cap were not attached to the crankshaft and were not recovered.
The #2 and #6 connecting rods displayed heat damage, while the #4 connecting rod did not show such damage. Metallurgical examination of the recovered portions of the #4 connecting rod indicated failure modes consistent with overstress, but no evidence of a primary failure mode was evident on the recovered components.
Maintenance Records
A review of the engine maintenance records disclosed that the #2 cylinder had been removed, repaired, and re-installed 1,020 flight hours prior to the accident. No other significant maintenance findings were reported.
Outcome
The aircraft was ditched in the ocean. The investigation did not determine a specific primary cause for the connecting rod fracture, as the metallurgical examination showed overstress but could not identify an initiating failure mode.