CEN09LA494

The experimental light sport airplane experienced a total loss of engine power after takeoff. The pilot then performed a forced landing to a corn field. Examination of the airplane revealed that the crankshaft had fractured near the engine flywheel due to the separation of the flywheel. The separated flywheel precluded further rotation of the crankshaft. Metallurgical examination of the flywheel separation revealed a high-cycle fatigue fracture of the crankshaft.

On July 23, 2009, at 1900 central daylight time, an experimental light sport Crisman Flightstar IISC, N5008E, experienced a total loss of engine power after takeoff. The airplane sustained substantial damage on impact with terrain during a forced landing on a field near Malta, Illinois. Visual meteorological conditions prevailed at the time of the accident. The sport pilot and passenger were uninjured. The 14 CFR Part 91 personal flight was originating at the time of the accident. The pilot departed from a private grass air strip when the engine experienced a total loss of engine power about 150-200 feet above ground level. The pilot then performed a forced landing on a corn field. The airplane sustained structural damage to both wings and the fuselage. The airplane was powered by a Hirth 2704, serial number 895034, engine that accumulated a reported total time of 127 hours. The pilot stated that the engine was purchased in April 2009 from the previous owner. At the time of purchase, the engine had been broken-in and accumulated two hours of operation. The pilot stated that he had been contacted by the Hirth distributer for the replacement of the flywheel to preclude crankshaft failure. The pilot then obtained and installed a replacement flywheel from the Hirth distributer and then repeated the engine break-in for an additional two hours. According to the Hirth distributer, the engine was subject to a replacement of the flywheel to preclude crankshaft failure. If the engine had accumulated zero hours of time, then only the flywheel had to be replaced, which could be performed by Hirth or outside maintenance personnel; however, if the engine had been run, then the engine would have to be sent to Hirth so that non destructive testing of the crankshaft could also be performed. The flywheels were being replaced due to a manufactured imbalance in the flywheel. External inspection of the engine revealed that the starter ring(flywheel) assembly had separated. The starter ring (flywheel) assembly was contained within the crankshaft housing and was resting against the internal portion of the housing and the crankshaft, which had precluded rotation of the crankshaft. Examination of the starter ring (flywheel) and crankshaft revealed that the crankshaft was fractured along a left-handed helical plane, 45 degrees to the crankshaft’s longitudinal axis immediately forward of the starter ring (flywheel). The orientation and appearance of the fracture surface was consistent with torsion-driven fatigue crack across 86 percent of the fracture with the remaining fracture consistent with overstress or unknown due to subsequent damage. Crack arrest marks were traced back to a single initiation site. When viewed from the side, wear marks were observed beginning at this location where the shaft engaged the taper on the starter ring (flywheel).