Circumstances
On February 20, 2012, at approximately 11:20 local time, an AT-3 R100 aircraft, registration F-GURV, was conducting an instructional flight in the Pontoise Terminal Maneuvering Area. While in level flight, the engine suddenly stopped. The instructor announced the engine failure over the radio and executed a forced landing in a field near Le Bellay en Vexin (95). The aircraft sustained damage to the engine.
Engine Examination
Post-incident examination of the Rotax 912 S2 engine revealed that metallic debris had blocked the rotating assemblies inside the crankcase, causing the engine to stop. The debris was traced to a spacer used for mounting the starter. The starter installed on the engine was equipped with two spacers, as per the manufacturer's documentation. The metallic debris originated from a third spacer that had been inside the engine.
Engine History
The engine was manufactured on July 14, 2011, and installed new on the aircraft on October 28, 2011. At the time of the event, it had accumulated approximately 150 hours of operation. All maintenance on the engine had been performed by the same Part 145 approved maintenance organization.
Maintenance
The Rotax 912 S2 engine can be equipped with two types of electric starters: a 0.9 kW starter that does not require spacers, and a 0.6 kW starter that requires two spacers. During factory assembly, this engine was fitted with a 0.9 kW starter and delivered in that configuration to the maintenance workshop. Due to space constraints on the AT-3 aircraft, the original starter was replaced with a 0.6 kW starter. The maintenance technician who performed the exchange did not recall any issues during installation. During this maintenance operation, it is possible that a spacer was inadvertently introduced into the engine crankcase.
The assembly line for this engine type handles both 0.6 kW and 0.9 kW starters. The probability of an error during the factory assembly process was considered low.
Conclusion
The safety investigation determined that the engine stoppage was due to the blockage of rotating assemblies by a metallic piece. The investigation could not determine how the piece came to be inside the crankcase.