What happened
On February 6, 1999, an amateur-built Orion G801, registration F-PJDL, was performing a local flight departing from Caen. After approximately thirty minutes of flight, the pilot experienced intense vibrations followed by a complete engine failure. The pilot subsequently performed a forced landing in a plowed field near Percy en Auge.
During the landing sequence, the aircraft's landing gear was torn away, and the aircraft underwent a ground loop (nose-over), resulting in damage to the landing gear and the underside of both wings.
The investigation
Investigators examined the wreckage and discovered that the propeller drive shaft, which connects the engine to the propeller, had fractured into three distinct pieces. The first section remained attached to the propeller, while the middle section was found in the rear fuselage. The remaining section, still attached to the engine output, had struck the fuselage near the flight control cables, causing visible damage to the airframe.
Microscopic analysis of the shaft revealed that the component was a steel tube originally intended for heavy-duty trailer use. The investigation focused on the metallurgical state of the fracture surfaces. Scanning Electron Microscopy (SEM) identified fatigue striations and micro-cracks, particularly in areas where the shaft had undergone previous welding and grinding for dynamic balancing.
Findings
- The primary cause of the accident was the failure of the propeller drive shaft due to fatigue and corrosion.
- The shaft had been subjected to multiple successive balancing procedures, which involved welding weights and grinding the surface. These processes introduced metallurgical defects, including porosities and cracks, and created stress concentrations.
- The use of a long drive shaft in a pusher configuration amplified any imbalances, increasing the mechanical load on the component.
- The presence of moisture and the seasonal environment likely contributed to fatigue-corrosion, accelerating the crack propagation from the weakened weld zones.