What happened
On August 4, 2015, a private Hughes 369HS (MD500) helicopter, registration D-HBRM, was performing a flight between two helisurfaces located a few kilometers apart in Ramatuelle, France. The flight was being conducted by a pilot accompanied by one passenger.
During the final approach, at an altitude of approximately 150 meters, the pilot observed a sudden decrease in the power turbine speed (N2), which dropped to approximately 85%. The pilot attempted to correct the speed using the power turbine governor trim switch but was unable to restore the engine to its normal operating range. In an attempt to reach the intended helisurface, the pilot lost control of the aircraft's airspeed, resulting in a hard landing in an area prior to the chosen landing zone. The aircraft sustained heavy damage.
The investigation
The investigation focused on the cause of the N2 speed decay and the pilot's response. Investigators examined the wreckage and the Rolls-Royce 2 .50-C18C engine, performing bench tests which showed the engine was functioning nominally. Fuel samples were analyzed and found to meet all required specifications with no anomalies detected. The aircraft's weight and center of gravity were within manufacturer limits at the time of the accident.
Regarding the pilot's actions, the investigation noted that while the N2 and NR (rotor RPM) indicators were overlapping, the pilot prioritized using the governor trim switch to restore power rather than following the established emergency procedures for an underspeed condition.