What happened
On August 22, 2004, a private Colomban MC 15 « Cri-Cri» (registration F-PZIQ) was conducting a cross-country flight from Saumur to Bourges. At approximately 19:30 local time, while flying at an altitude of 800 feet near Valençay, the propeller hub and cone assembly of the right JPX PUL-252 engine detached from the aircraft in flight.
Upon the separation of the assembly, the pilot immediately reduced power on both engines and gradually increased the 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 aerodrome in Bourges without further incident.
The investigation
The investigation focused on the mechanical failure of the right engine's propeller assembly. The aircraft was maintained by the pilot, who had previously replaced the right engine's crankshaft in 2001. Following that replacement, the pilot had performed dye penetrant inspections on the components, which had shown no defects at that time.
Technical examination of the propeller attachment bolt and the propeller flange revealed that both components had failed due to fatigue. The fractures originated from localized stress points caused by bending and torsional forces. No metallurgical defects were identified at the initiation sites. The investigation determined that the simultaneous failure of both the bolt and the flange likely originated from a single, unidentified event affecting the alignment or loading of the components.