What happened
On March 18, 2005, a Robin DR 40 and 120 aircraft, registration F-GFXF, departed from Châteauroux Villers for a local flight. During the initial climb, the pilot noticed a significant drop in engine RPM, fluctuating between 400 and 500 RPM. After an aborted flight and a subsequent ground inspection by a maintenance technician that revealed no anomalies, the pilot attempted a second departure.
Approximately twelve minutes into the second flight, while at an altitude of 1,500 feet, the pilot felt light vibrations from the Lycoming engine. These vibrations intensified shortly thereafter, accompanied by a loss of power that made maintaining level flight impossible. The pilot issued a distress message on 123.5 MHz, configured the flaps to 15 degrees, and selected a landing site. Before touchdown, the pilot shut down the engine and performed an emergency landing in a cultivated field with the flaps extended to 40 degrees. There were no fatalities or injuries reported.
The investigation
The investigation focused on the engine's mechanical state and recent maintenance history. The engine had completed 6,420 total hours and 2,050 hours since its last overhaul. Investigators discovered blue silicone paste applied to the base gaskets of all four cylinders and the through-bolts.
Upon detailed examination of the engine, investigators found a broken connecting rod cap on cylinder number 3. They also identified fretting corrosion on the mating surfaces of the two crankcase halves near the bearings, caused by micro-movements. Furthermore, the two half-shells of the central bearing had rotated, and debris from the damaged anti-friction metal had accumulated, eventually clogging the oil lubrication hole in the central journal.