What happened
On August 22, 2004, a privately operated Colomban MC 15 "Cri-Cri" was conducting a cross-country flight from Saumur to Bourges. While cruising at approximately 800 feet near Valençay, the propeller hub, cone, and assembly from the right JPX PUL-252 engine detached from the crankshaft.
Upon the loss of the propeller assembly, the pilot immediately reduced power on both engines and gradually increased power on the remaining left engine. The pilot maintained control of the aircraft and climbed to 1,800 feet. After approximately 40 minutes of flight operating on a single engine, the pilot successfully landed at the destination in Bourges without further incident.
The investigation
The investigation focused on the mechanical failure of the right engine's propeller mounting components. The examination of the propeller-to-crankshaft attachment bolt and the propeller plate revealed that both components had failed due to fatigue. These fractures originated from localized stress points caused by bending and torsional forces.
Investigators noted that no metallurgical defects were present at the initiation sites. Because of the specific positioning of these cracks relative to the crankshaft axis, it was determined that both failures likely originated from a single, unidentified event. The pilot, who performs his own maintenance, had previously replaced the right engine's crankshaft in 2001 and had performed dye penetrant inspections on the components, which had shown no defects at that time.