Incident Overview
On 20 March 1993, a commercial helicopter flight from Romont to Würenlingen ended abruptly when the aircraft struck a paraglider tow cable. The helicopter, an AS 350 B2 Ecureuil registered as HB-XUU, carried two crew members and four passengers. A second helicopter of the same type followed behind.
Flight Sequence
The helicopter was cruising at approximately 200 km/h at an altitude of 270 m above ground when the pilot noticed a paraglider at an estimated 500 m to the right. The pilot radioed the other helicopter and turned left to maintain separation. Suddenly, a loud noise was heard. Believing it was a bird strike, the pilot initiated an immediate emergency landing.
Collision Details
After landing, the crew found cable fragments wrapped around the rotor mast. The cable, measuring 2 mm in diameter and 140 m in total length, was black-sheathed and came from a winch mounted on a private vehicle. The paraglider pilot, who was being towed, released the cable as the helicopters approached, but the main rotor blade struck it. The cable impacted the right upper windshield and wrapped around the mast. Due to its low tensile strength (tested at 220–230 kg), the cable broke without affecting helicopter controls, allowing a normal emergency landing.
Investigation Findings
The investigation confirmed the helicopter had no pre-existing technical defects, was within weight and balance limits, and the pilot held a valid professional license with no health impairment. The paraglider pilot also held a valid license and used a Phantom 45 paraglider (registration 8559). The winching activity was not listed in the NOTAM for that week, and no permission had been sought. The airfield manager of Bellechasse had been informed at 12:30 about limited towing operations, but only local glider pilots were notified—other airspace users were unaware.
Weather Conditions
At the time of the accident, the sky was partly cloudy (3-5/8 Cirrus), visibility 5–8 km, wind variable at 2 kt, temperature 16°C, dewpoint 5°C, QNH 1021 hPa, and sun azimuth 221° with elevation 35°.
Conclusion
The accident was determined to result from a collision with a nearly invisible, unauthorized cable at an altitude exceeding 150 m above ground. The assessment noted that such winch-towing operations pose a hazard incompatible with flight safety norms.