Mc Entire Jngb Airport
Aircraft Accident/Incident Report

Eastover, South Carolina 29044
Tuesady, April 3, 2012 14:00 EDT

The pilot reported that, about 25 minutes into the second flight of the day, the engine began to run roughly. The pilot checked the magnetos and noted that all four cylinder head temperatures and all four exhaust gas temperatures were normal. He reduced engine power to 20 inches and 2,000 rpm, but the engine roughness increased, and the oil pressure dropped to 0 about 1 minute later. The pilot then completed a forced landing to a nearby National Guard base, but he could not completely align the airplane to the runway after it encountered the wake turbulence of a military jet departing in the opposite direction. The airplane landed at a 20- to 30-degree angle to the runway, veered off the right side, and struck a “runway remaining” sign before coming to a stop. After deplaning, the pilot saw engine oil covering the airplane’s nose landing gear and the landing gear doors. Subsequent engine examination revealed that the No. 1 cylinder upper aft through bolt was sheared off, that the two No. 1 cylinder upper mounting studs had pulled loose from the crankcase, and that the crankcase at the No. 1 cylinder aft lower through bolt was cracked and separated; oil was leaking near it. Internal engine examinations revealed pitting and a frosty appearance of the metal on the Nos. 2 and 3 upper main bearing support webs consistent with fretting, which is typically a result of inadequate or loss of preload tension to fasteners. According to maintenance records, the engine underwent a major overhaul in 2002. In 2007, after about 490 hours of operation, a hairline crack was found in the engine case. The engine was disassembled and then reassembled with a rebuilt case. In 2010, after about 303 hours of operation, intake pipes were found loose on the Nos. 1 and 2 cylinders, and one exhaust nut was missing from the No. 1 cylinder. Five cylinder hold-down studs were also found broken on the No. 2 cylinder. The missing nut was replaced on the No. 1 cylinder, and the intake pipes were resealed. The No. 2 cylinder was removed, the studs were replaced, and the No. 2 cylinder was then reinstalled. It could not be determined when the fretting began due to the multiple opportunities during which the through bolt preload tension could have been affected. However, by the time of the accident, the fretting had progressed sufficiently that it likely resulted in excessive loads to the fractured through bolt, loosened the cylinder studs, and subsequently twisted the cylinder, which then fractured the crankcase. 

Inadequate or loss of through bolt preload tension, which resulted in fretting between the engine halves, the subsequent failure of one cylinder through bolt, the loosening of additional cylinder retaining studs, and the fracture of the crankcase. Contributing to the accident was the wake turbulence of a departing military jet, which resulted in the pilot’s inability to completely align the airplane with the runway.