Accident Details
The pilot was maneuvering an agricultural airplane to enter a field and commence spraying. At 120 feet above ground level, the engine lost power. The pilot attempted to restart the engine, but it did not restart. During the ensuing forced landing, the airplane contacted circular rows of cotton before coming to rest upright.
Examination Findings
The engine was examined at the manufacturer's facility. Silicon sealant was observed on the base flanges of cylinders #1, #2, #4, and #6, and on the crankcase mating surfaces. Fretting was observed on the base flanges of the cylinders, on the mating surface of the crankcase halves, and on the main bearing bosses. The #2 main bearing was found fragmented, and its bore was cracked and damaged. Additionally, the crankshaft was fractured between the #2 main bearing and #3 crankshaft cheek. According to a TCM metallurgist, the fatigue fracture's origin was determined to be at the aft radius of the #2 main bearing.
Cause
The silicon sealant prevented proper torqueing of the bolts that mate the crankcase halves, leading to vibration at the crankcase mating surfaces. This vibration caused the #2 main bearing to shift and fail, resulting in a loss of engine power.