What happened
On February 17, 2001, a Robin DR 400-140 B aircraft, registered F-GOVG, was conducting a flight from Toulouse Lasbordes toward Graulhet for the purpose of performing touch-and-go maneuvers. While cruising at 1,600 feet, the pilot heard a heavy thud and felt vibrations, which they initially attributed to the engine.
Following the initial noise, the pilot performed standard troubleshooting procedures, including checking the mixture, magneto selection, fuel pump, and fuel supply. During a turn back toward Graulhet, the pilot reduced power, at which point the noise and vibrations intensified significantly, ultimately leading to the complete seizure of the propeller. The pilot, carrying three passengers, prepared the occupants for an emergency and executed a forced landing in a field near Ambres. During the landing roll, the aircraft passed under medium-voltage power lines and an irrigation ramp, but the aircraft sustained no significant damage beyond the engine.
The investigation
The investigation focused on the mechanical failure of the Lycoming 0-3ered-D2A engine, which had accumulated 2,190 flight hours and was operating under a second life extension. Upon disassembly of the engine, investigators identified a primary fatigue fracture in the fifth crankpin of the crankshaft, specifically at the fillet of the third big end.
Findings
- The investigation established that the crankshaft fracture was the primary cause of the engine failure.
- Analysis of the fracture surface markings indicated that the fatigue crack had initiated at least 60 flight hours prior to the accident.
- Due to significant surface deformation (matage) at the failure site, investigators could not rule out the possibility that the crack had actually formed before the engine reached its standard 2,000-hour service limit.