Incident Summary
A banner towing flight over the ocean ended when the engine lost power, forcing the pilot to ditch the airplane in the water. The aircraft touched down short of the beach, nosed over, and came to rest inverted.
Engine Failure and Ditching
During cruise flight, the engine began to run rough and lose a significant amount of power. The pilot attempted corrective measures, including applying and removing carburetor heat and releasing the banner, but the engine continued to lose power. As the engine was not producing enough power for continued flight, the pilot executed a water landing.
Post-Accident Examination
Examination of the engine revealed that the number 4 piston had fractured around its circumference just above the connecting rod pin. The fracture exhibited beach mark signatures consistent with cyclic fatigue. Fractured pieces of the piston were found in the oil sump. The aft piston pin end cap was worn and burnished, while the forward piston pin end cap had separated from the piston pin with fracture surface signatures consistent with overload. The rod journal bearing was also worn and burnished.
The number 4 connecting rod journal of the crankshaft was cracked, and the connecting rod cheek on the crankshaft was fractured perpendicular to the rod journal. The journal cheek fracture exhibited beach marks consistent with cyclic fatigue. The fracture had an irregular shape that provided a "key" maintaining rotational continuity of the crankshaft during operation; however, it also allowed the crankshaft to flex. This flexing induced rotational misalignment of the connecting rod, which in turn caused cyclic fatigue failure of the piston. The condition was likely ongoing for some time prior to the final fatigue failure.
Additionally, copious amounts of small metal debris and flakes, consistent with the rod end cap bearing material, were retrieved from the oil pressure filter screen. Such debris should have been apparent if the screen and filter were being checked for contaminants on a regular basis.
Maintenance Findings
Lycoming Mandatory Service Bulletin (SB) No. 480E recommends an oil change, pressure screen cleaning, and oil sump screen check at 25-hour intervals. The SB states that observation of abnormal metal content during the service may indicate additional service is required. Examination of maintenance records revealed that 112 hours had elapsed since the last 100-hour inspection at the time of the accident. The aircraft and engine logbooks contained no record of the operator following the recommended procedures as set forth in SB 480E.