Accident Overview
During cruise flight, the engine produced a loud bang followed by a loss of power. The propeller continued to windmill, and the engine did not respond to control inputs or restart attempts. The pilot declared an emergency and chose to land in an open area within a timberland. The approach progressed normally until touchdown, when the main wheels contacted the ground first. The nose wheel subsequently dug into the terrain, separated from the aircraft, and the airplane flipped over before coming to a stop. Both the pilot and passenger exited the airplane unassisted.
Engine Examination
Post-recovery examination revealed a loss of continuity in the engine. The engine was transported to the manufacturer for a teardown inspection. The crankshaft was found separated at the No. 2 main bearing. The crankshaft and crankcase halves, along with associated parts, were examined at the NTSB Materials Laboratory. The crankshaft had fractured through the aft cheek of the No. 2 main bearing journal. Optical examination showed features typical of fatigue propagation, including smoothly textured surfaces with curved arrest lines on the forward fracture. Ratchet marks indicated that fatigue initiated at multiple locations on the surface of the aft radius of the main journal surface, with rearward propagation through the crank cheek. The fatigue initiation site was located at the approximate tangent point between the aft journal radius and the face of the forward face of the cheek. The surface of the No. 2 main journal was circumferentially roughened but not deeply gouged, with local areas exhibiting heat tinting. Other main and cylinder journals displayed some local damage, but none as extensive as the No. 2 main journal. The No. 2 main bearing shells were fractured and broken into several pieces, many of which were not recovered. The remaining bearing shells were intact and showed varying levels of wear, damage, and debris embedment. The bearing shells were identified as FAA-PMA part numbers SA642720M10, indicating 0.010-inch oversize bearings.
Maintenance History
According to engine logbooks, the engine last received a major overhaul on April 22, 1998, 1,354 flight hours before the accident. On August 27, 2004, 315 flight hours before the accident, all six cylinders were replaced with new cylinders. On September 5, 2005, 141 flight hours before the accident, the airplane underwent an annual inspection. On July 8, 2006, approximately three hours before the accident, maintenance was performed on the engine's turbocharger.