Accident Description
The pilot of the airplane reported that, while in cruise at an altitude of 7,000 feet, the engine ceased operation without any prior warning. The pilot noted that the engine quit as though the magnetos had been turned off, with no sputtering or gradual loss of engine power. Following the engine failure, the pilot executed a forced landing to a field, where the airplane came to rest upright.
Examination Findings
Postaccident examination of the engine focused on the crankshaft idler gear assembly. The examination revealed that the upper retaining screw for the crankshaft idler gear had separated from its position. The lower retaining screw was found intact; however, it exhibited excessive wear. Additionally, the bolt hole for the lower screw was severely elongated, indicating significant stress or movement.
Metallurgical Analysis
Metallurgical examination was conducted on the separated upper retaining screw. The analysis determined that the screw had fractured due to high stress, low cycle fatigue. The examination further indicated that the upper screw most likely fractured after the lower screw had come loose, based on the condition of the components.