What happened
On 1 July 2009, a Hughes 369D helicopter, registration SE-JBU, was engaged in a reindeer herding operation in the Dalarna region of Sweden. While the aircraft was hovering at a low altitude of approximately 10 to 12 meters above a boggy area north-north-west of Klutsjön, a loud bang was heard, followed by intense vibrations and a total engine failure.
Because the aircraft was operating at a low speed and altitude, the pilot was unable to establish a controlled autorotation. The helicopter descended rapidly and struck the ground with a high sink rate. The impact caused the right landing skid to break and the aircraft to tip, resulting in the main rotor blades striking the terrain. The pilot and an assistant on board sustained minor injuries but were able to exit the wreckage and contact emergency services.
The investigation
Investigators from the Swedish Accident Investigation Board (SHK) conducted a technical examination of the engine and the aircraft's drive shaft line. The investigation focused on the mechanical failure of the engine compressor-to-turbine coupling. Metallurgical analysis revealed that a component known as the Splined Adapter had failed due to a fatigue crack. This crack was believed to have been initiated by fretting damage on the exterior of the adapter.
Technical scrutiny also examined the maintenance history and the engine's design. The investigation noted that the condition of the Splined Adapter cannot be inspected during routine service without dismantling the engine. Furthermore, the investigation looked into the effectiveness of existing safety measures and the operational capabilities of search and rescue (SAR) resources following the incident.