What happened
On May 17, 1963, a Bell 47G-2 helicopter, registration HB-XAW, operated by Schweizerische Helikopter A.G., departed Locarno for a commercial mission involving snow measurements. The flight carried two engineers to the Greina-Lukmanier region. Upon reaching the upper Val Camadable, the pilot identified a suitable landing site near a plateau at approximately 2,000 meters.
During the final approach to the landing site from the south, the aircraft encountered sudden, strong downdrafts. The pilot attempted to increase power and blade pitch to maintain the approach, but the downward air currents prevented the aircraft from reaching the intended spot. In an attempt to regain altitude by maneuvering away from the terrain, the pilot initiated a left turn, but the rotor RPM decreased, making a ground impact unavoidable. The helicopter struck the terrain approximately 40 to 50 meters from the target site. The aircraft slid 25 meters before the right skid struck a rock, causing the helicopter to pivot sharply and tip onto its left side. There were no injuries to the pilot or the two passengers.
The investigation
The investigation examined the meteorological conditions, the flight profile, and the aircraft's performance capabilities. It was established that while the general weather forecast indicated north-easterly winds, there was no specific warning for downdrafts on the southern side of the Alps. The investigation also reviewed the pilot's flight experience and the technical state of the Bell 47G-2, finding no mechanical defects or health issues contributing to the accident.
Findings
- The primary cause of the accident was the unexpected downdraft that prevented the completion of the landing.
- The pilot approached the landing site without first performing a wind reconnaissance flight at low altitude to assess local conditions.
- The approach was executed at an altitude and direction that left insufficient performance margin to safely abort the landing or transition to a safe flight path once the downdraft occurred.
- The terrain, characterized by rocky and snow-covered surfaces, contributed to the significant damage to the main and tail rotors, fuselage, and landing gear.