What happened
On January 18, 2011, a Robinson R22 Beta helicopter, registration HB-ZKL, departed from Barcelonnette, France, bound for Bex, Switzerland. The pilot, accompanied by one passenger, intended to fly past his home in Châtel to greet his family before completing the flight.
During the approach, at an altitude of approximately 1,200 meters, the pilot deactivated the carburetor heat control that had been in use since takeoff. As the pilot positioned the aircraft facing the house, he reduced speed to achieve a near-stationary hover out of ground effect (OGE). Upon attempting to increase power for the go-around, the aircraft experienced a sudden sink and a rightward yaw. The pilot reported a drop in rotor RPM and observed the "LOW RPM" amber warning. In an attempt to recover, the pilot initially pulled on the collective, then lowered it to regain RPM, before finally pulling fully to cushion the impact with the ground. The impact resulted in the destruction of the aircraft and two injuries (the pilot and the passenger).
The investigation
Investigators examined the wreckage and found no mechanical anomalies capable of explaining the crash. The investigation established that the helicopter was at its maximum takeoff weight at the time of the flight. While flight manual performance curves indicated the engine was not at its absolute power limit during the OGE hover, the rightward yaw during the power increase confirmed that the pilot had requested a surge of power that the engine could not deliver, leading to the decay in rotor RPM.
Further analysis revealed that the pilot had deactivated the carburetor heat to seek additional power during the go-around. Environmental conditions at the time included a temperature of 0 °C and 80% relative humidity, conditions conducive to carburetor icing. Additionally, while the pilot's previous flight to the site involved a much lighter passenger, the passenger on the day of the accident weighed 85 kg.