What happened
On January 20, 2024, an Airbus Helicopters EC135T2+, registration HB-ZUI, was performing a medical repatriation flight near Rougemont, Switzerland. The crew, consisting of a pilot, a paramedic, and a physician, had just refueled at Saanen Airport and was climbing toward Avoriaz, France, for a follow-up mission.
During the climb, the pilot observed a needle split on the First Limit Indicator (FLI) between the two engines. Seconds later, the right engine failed spontaneously, triggering cockpit warnings. The Full Authority Digital Engine Control (FADEC) automatically adjusted the remaining left engine to One Engine Inert (OEI) mode. The pilot executed a safe return to Saanen, landing on runway 08 without further incident.
The investigation
Following the event, the Swiss Transportation Safety Investigation Board (SUST) examined the engine and the aircraft. While no external anomalies were visible on the engine, investigators discovered metallic debris during a check of the reduction gearbox magnetic plug.
In collaboration with the French BEA and the engine manufacturer, the investigation focused on the Arrius 2B2 engine. The examination revealed that the accessory drive train gear had been destroyed, with damage extending to other gears within the assembly. The investigation traced the failure to a fatigue fracture originating at the surface of a tooth foot.