What happened
On June 6, 1968, an Agusta Bell 47 J-3 B-1 helicopter, registration HB-XCA, was returning to Sion after participating in an aviation demonstration in Bad Ragaz. While flying near the Oberalp Pass in Switzerland, the aircraft struck the cables of a cable car system located near the Pazola area. The impact occurred at an altitude of approximately 40 meters above the ground. Following the collision, the aircraft's tail section was severed as the fuselage was forced into the path of the main rotor, causing the helicopter to spin and crash onto a snow-covered slope. The pilot, who was the sole occupant, was killed in the crash, and the aircraft was completely destroyed.
The investigation
Investigators examined the wreckage and the site of the impact, which was located roughly 3 km west of the Oberalp Pass. The investigation established that the helicopter's left skid support struck the cable car's carrier cables. The force of the impact caused the cable to slide along the skid until the skid horn broke. This sudden movement caused the aircraft to pitch forward, leading the main rotor blade to strike the rear fuselage and sever the tail boom. Witnesses, including railway workers performing maintenance on nearby catenary lines, observed the collision. Additionally, the investigation reviewed the pilot's flight history, the aircraft's maintenance records, and local meteorological conditions, which included moderate turbulence and wind gusts.
Findings
- The pilot was flying at an altitude significantly below the minimum safety height prescribed by air regulations.
- The pilot failed to see the cable car cables, which were nearly invisible in the terrain.
- The collision with the cables caused structural failure, including the loss of the tail rotor and the destruction of the tail boom.
- While the aircraft had sufficient power to handle the prevailing wind conditions, the low-altitude flight path made the obstacle unavoidable once encountered.