What happened
On September 25, 1966, at approximately 17:30 local time, an Agusta-Bell 47J-3B-1 helicopter, registration HB-XBX, was engaged in a rescue mission near Bannalp, Switzerland. The mission was initiated by the Swiss Rescue Flight Service (SRFW) to recover a mountaineer who had suffered a broken leg following a fall.
After locating the injured individual in a steep scree slope, the pilot determined that transporting the victim to the helicopter was not feasible due to time constraints. To facilitate the loading of a stretcher, the pilot removed both cabin doors. While attempting to hover near the slope and rest the right skid on a small rock platform to pick up the patient, the main rotor blades struck the terrain. This impact caused the aircraft to rotate violently, capsize, and subsequently catch fire. The helicopter was completely destroyed in the accident.
The investigation
An investigation conducted by the Swiss Flight Accident Investigation Commission established that the aircraft was in a serviceable condition at the time of the accident. The engine and airframe had undergone recent maintenance, including a 600-hour overhaul earlier that year.
Investigators examined the wreckage and the terrain, identifying metal transfers on the rock surface at the rotor level, which confirmed that the blades had made contact with the slope. The investigation also reviewed the pilot's credentials, noting significant experience in helicopter operations, and found no evidence of health issues or poor weather conditions that contributed to the event.
Findings
- The primary cause of the accident was the main rotor striking a rock formation during a stationary hover.
- The impact caused an immediate change in engine torque, leading to a rapid 45-degree yaw and loss of control.
- The pilot may have overestimated the available clearance between the rotor blades and the rising terrain or failed to maintain sufficient attention to the ground clearance at the rotor plane during the approach.
- The pilot sustained spinal injuries and burns but successfully escaped the burning wreckage through the shattered windscreen.