What happened
On January 11, 2003, a Robinson R44 helicopter, registration F-GYDH, departed from Cannes-Mandelieu for a private pleasure flight in the Alpes-Maritimes region. The aircraft flew over the snowy terrain of the hinterland, including the ski slopes of Gréoliered-les-Neiges. During the flight, witnesses observed the helicopter following a ridgeline before hearing loud clattering noises. The aircraft then entered a vertical descent and struck a rock on the northern slope of Mount Cheiron, resulting in three fatalities (the pilot and two passengers).
Video footage recovered from a passenger's camcorder captured the final moments of the flight. The footage showed the aircraft performing a hover near the ground, which kicked up significant amounts of powdery snow. Shortly after, the aircraft began a climb toward the Cheiron ridge. During this phase, the engine noise changed, and the aircraft began to experience intense vibrations. Within seconds, the engine and rotor RPM dropped sharply to approximately 60%, leading to an aerodynamic stall of the rotor blades and a total loss of control.
The investigation
The investigation focused on the engine performance and the cockpit instrumentation. Investigators examined the wreckage and found that the engine was delivering very low power at the moment of impact. Laboratory tests confirmed that the engine governor and the low RPM alarm system were functional. However, the investigation noted that the rotor tachometer circuit breaker was found in the disengaged position, though video evidence suggested the tachometer was working normally prior to impact.
Analysis of the engine's manifold pressure showed that the pilot was operating the aircraft at high power settings that exceeded manufacturer limits for the given altitude and temperature. Specifically, at altitudes between 4,300 and 5,300 feet, the manifold pressure was observed at levels that exceeded the maximum allowable limits for those atmospheric conditions.
Findings
- The primary cause of the accident was the pilot's excessive demand for power via the collective pitch control, which exceeded the engine's available power at high altitude and weight.
- The engine and rotor RPM dropped significantly because the carburetor throttle reached full opening, leaving no further power available to compensate for the increased pitch.
- A contributing factor was the failure of the visual and audible low RPM alarms to alert the pilot, though the exact reason for this failure remains undetermined.
- Potential contributing factors included possible carburetor icing and the ingestion of snow into the air intake during the low-altitude hover, both of which may have further reduced available engine power.