NTSB Identification: LAX05LA273.
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Accident occurred Saturday, August 20, 2005 in Palos Verdes, CA
Probable Cause Approval Date: 02/26/2007
Aircraft: Piper PA-18-105, registration: N294T
Injuries: 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

During a banner towing flight over the ocean along the coast, the engine lost power and the airplane ditched in the water. While in cruise flight, the engine began to run rough and lose a significant amount of power. The pilot attempted corrective measures (applying and removing carburetor heat and releasing the banner), but the airplane continued to lose power. The engine was not producing enough power for continued flight and the pilot landed in the water short of the beach. When the airplane hit the water, it nosed over and came to rest inverted. Post accident examination revealed that the number 4 piston had fractured around the circumference of the piston just above the connecting rod pin and had 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. The forward piston pin end cap 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" that maintained rotational continuity of the crankshaft during operation; however, the fracture also allowed the crankshaft to flex. Flexing of the crankshaft induced a rotational misalignment of the connecting rod, which in turn induced the cyclic fatigue failure of the piston. This condition was likely on-going for some time prior to the final fatigue failure. Copious amounts of small metal debris and flakes were retrieved from the oil pressure filter screen that were consistent with the rod end cap bearing material and should have been apparent if the screen and filter were being checked for contaminants on a regular basis. 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 continues that observation of abnormal metal content during the service may indicate additional service is required. Examination of maintenance records revealed that it had been 112 hours 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.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

a loss of engine power due to the cyclic fatigue failure and separation of the number 4 piston.

Full narrative available

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