Aircraft and Operator
The accident involved a K-1200 K-MAX helicopter, registration HB-ZEH. This type is a single-engine heavy-lift helicopter known for its external load capabilities. The aircraft was operated by Eagle Helicopter AG, and its maintenance was entrusted to RUAG Aviation.
Accident Circumstances
On 2 October 2007, the helicopter was conducting a flight in the area of Strit, within the municipality of Illgau in the canton of Schwyz, Switzerland. The local time was Central European Summer Time (UTC+2). During the flight, the engine, a Honeywell T5317A-1 turbine, experienced a failure. The helicopter was at an altitude from which a successful autorotation—the emergency landing technique without engine power—could not be accomplished.
Investigation Findings
The Swiss Accident Investigation Board (SUST) investigated the accident under the provisions of Annex 13 to the International Civil Aviation Organization (ICAO) convention. The investigation included a detailed examination of the wreckage, the engine, and its accessories. The fuel control unit, oil pump, starter/generator, and the N1 accessory drive gearbox were inspected. The examination revealed damage to the bevel gear teeth and bearing wear. The cause of the turbine failure was determined to be a mechanical issue that led to a loss of engine power. The investigation also found that the distinctive signs indicating an impending turbine failure—such as those from the chip detection system—had not been addressed consistently.
Probable Cause
According to the final report, the accident was caused by a turbine failure at a height from which it was not possible to successfully carry out autorotation. Additionally, the distinctive signs of a turbine failure had not been addressed consistently.