What happened
On February 20, 2012, at approximately 11:20 local time, an AT-3 R100, registration F-GURV, was conducting an instructional flight within the Pontoise TMA. While the aircraft was in level flight, the engine suddenly ceased operation. The instructor notified the radio of the engine failure and subsequently executed a forced landing in a nearby field near Le Bellay en Vexin. While the aircraft sustained engine damage, there were no reported injuries or fatalities.
The investigation
The investigation focused on the ROTAX 912 S2 engine, which had approximately 150 hours of total time since its installation in October 2011. An examination of the engine revealed that metallic debris had entered the engine casing, where it blocked the rotating assemblies and caused the sudden stoppage.
Investigators identified the source of the debris as a spacer used during the installation of the starter motor. The engine was originally equipped at the factory with a 0.9 kW starter, which does not require spacers. However, due to space constraints within the AT-3 airframe, a maintenance facility had replaced the original unit with a smaller 0.6 kW starter. Unlike the 0.9 kW version, the 0.6 kW starter requires the use of two spacers.
Findings
- The engine failure was caused by metallic debris blocking the rotating components inside the engine casing.
- The debris originated from a third spacer that was not part of the required configuration for the 0.6 kW starter.
- It is believed that this extra spacer was inadvertently introduced into the engine casing during the maintenance procedure when the technician swapped the starter motors.
- While the factory assembly process for these engines is standardized, the investigation concluded that the error likely occurred during the local installation of the smaller starter motor.