What happened
On November 6, 2010, a Diamond DA 20-A1 (registration F-GVKP) was performing a local flight at the Lyon Brindas airfield. After completing two instructional exercises, the pilot began a final circuit to land on runway 01. During the downwind leg, the pilot adjusted the propeller to low pitch and reduced speed to approximately 7-0 knots while extending the first stage of flaps. At this moment, the engine suddenly stopped, and the propeller became locked. Despite multiple attempts by the pilot to restart the engine using the starter, the propeller remained immobile. The pilot subsequently performed a forced landing on the unpaved runway. There were no injuries and no damage to the aircraft.
The investigation
The investigation focused on the Rotax 912 S3 engine installed in the aircraft. Upon inspection on the ground, investigators found the crankshaft was seized. Significant wear was observed on the contact surfaces between the two crankcase halves, and friction marks were present on the camshaft and crankshaft bearings. Measurements of the bearing bores revealed dimensions smaller than the manufacturer's minimum specifications.
Investigators found that the engine, which had approximately 1,090 total operating hours, was subject to a maintenance program that referenced the Rotax maintenance manual but did not include the Rotax operator manual. While the engine manufacturer had introduced a redesigned crankcase in 2006 to address this specific wear issue, the engine in this accident was manufactured in 2005. Furthermore, the investigation revealed that the club's maintenance records noted difficulty with starting the engine during a previous 100-hour inspection, though no specific action was taken regarding the propeller rotation resistance.
Findings
- The engine failure was caused by excessive wear between the crankcase halves, which reduced necessary clearances and led to the seizure of the crankshaft.
- The primary contributing factor was a lack of awareness regarding the Rotax operator manual's instructions, specifically the requirement to check for excessive propeller resistance during daily pre-flight inspections.
- Communication from the engine manufacturer regarding the implementation of these new inspection procedures was insufficient.
- The procedure of manually assessing propeller resistance is considered potentially unsuitable for flight club environments, as pilots may lack the experience to distinguish between normal and abnormal resistance.