What happened
On 3 September 2012, a Robinson R44 helicopter, registered EC-IVT, departed from Clermont Ferrand Auvergne aerodrome bound for Luc Le Cannet. The flight was being conducted as a private general aviation mission with the pilot and one passenger on board.
During the cruise phase, the aircraft was flying at approximately 4,200 ft. At around 10:35, while traveling at a ground speed of 115 kt, the helicopter experienced an in-flight break-up and collided with the ground in a mountainous area. The impact resulted in two fatalities and the total destruction of the aircraft.
The investigation
The investigation focused on the wreckage, which was scattered over 500 meters. Investigators established that one of the main rotor blades had struck the front of the airframe, causing the structural failure. Physical evidence showed that the rotor mast was bent, a characteristic sign of rotor mast bumping.
Further examination of the aircraft revealed that the cabin heating was active and that an assembly screw from the air heat exchanger had perforated the exhaust manifold prior to the accident. Testing of the onboard carbon monoxide warning system revealed a significant malfunction; the system failed to trigger even when exposed to concentrations of 3,500 ppm, far exceeding the expected 50 ppm threshold.
Medical examinations of the pilot following the accident revealed a carbon monoxide level of 16%, which is significantly higher than normal levels and capable of causing impaired judgment, nausea, and vertigo.