What happened
On October 20, 2002, a Robinson R44 helicopter, registration F-GXAT, departed from Chambéry for a flight to the Chalet du Roc de la Pêche, located at an altitude of 1,900 meters. After a 90-minute stop at the chalet, the pilot attempted a departure to return to Chambéry. During the takeoff, the pilot maintained a low altitude and began accelerating. As the aircraft crossed a precipice, witnesses reported hearing engine irregularities and observing the helicopter lose altitude before striking the ground. The impact resulted in three fatalities, including the pilot and two passengers, and the total destruction of the aircraft.
The investigation
Investigators examined the wreckage at the crash site, a small rocky spur near the Chavière valley. Analysis of the airframe and engine revealed that the engine was functioning correctly and was still delivering power at the moment of impact, as evidenced by the torsion of the rear transmission and the displacement of the drive belts. While the rotor blades showed signs of low RPM during the impact, no mechanical failure prior to the accident was identified. \nPerformance calculations determined that while the aircraft's weight was within limits for landing in ground effect, it exceeded the maximum allowable mass for a hover out of ground effect (OGE) at that altitude. The investigation also noted that the pilot's flight path was unusually short, likely an attempt to avoid climbing too high, which led the aircraft into a critical transition phase.
Findings
- The aircraft's total mass was greater than the maximum allowable mass for hover out of ground effect at the departure altitude.
- The pilot transitioned from a hover to forward flight at a low airspeed, causing the aircraft to exit ground effect.
- Insufficient consideration of the aircraft's performance limitations for high-altitude takeoff out of ground effect was the primary cause of the accident.