What happened
On July 29, 1992, at approximately 13:55 local time, an Airbus Helicopters AS 350 B2 helicopter, registered as HB-XYC, was operating in the Verzasca Valley in the canton of Ticino, Switzerland. The aircraft, owned by XME SA and operated by Heli-TV SA, was engaged in external load operations involving the transport of hay nets.
The pilot and a flight assistant had departed from Vogorno around 13:30 after lunch. They performed several small material transports before heading north toward Lavertezzo. The pilot intended to pick up a pre-tied hay net located approximately 50 meters north of San Bartolomeo. While approaching the loading point at low altitude and slow forward speed, the helicopter collided with one of three cables belonging to a 16 kV high-voltage power line. The impact caused the aircraft to crash from a height of roughly 25 to 30 meters. The helicopter came to rest on its right side, partially overturning as it slid down an embankment. Both the pilot and the flight assistant sustained fatal injuries and did not survive.
The investigation
The Swiss Transportation Safety Investigation Board (STSB) conducted a preliminary inquiry that concluded in November 1993. Investigators examined the wreckage, medical reports, and operational records. The helicopter was destroyed, but forensic analysis of the main rotor blades showed they remained attached to the mast, with power line cable partially wrapped around it. No fire occurred.
The pilot, born in 1939, held a valid Professional Pilot License (helicopter) issued in 1969 and had flown approximately 15,475 hours total, including 1,500 hours on the AS-350 type. His last medical check was clear. The flight assistant had no flying experience or license. Weather conditions were typical for a hot summer day: visibility around 8–9 km, scattered clouds at 1,300 meters, and temperatures of 27°C with high humidity.
Crucially, the power line involved was not marked on the 1:100,000 obstacle chart used by the pilot. Although the line had been notified to authorities in 1965,当时的 criteria did not require its publication or marking because it was deemed less critical than other obstacles. The line’s maximum height above ground was approximately 60 meters, but the specific section where the collision occurred was lower.
Findings
The investigation excluded technical failure of the helicopter as a cause. Medical evidence confirmed no alcohol or drugs were present in the pilot’s system. The primary finding was that the accident resulted from the collision of the helicopter with an air navigation obstacle (power line cable).
Investigators noted that the pilot likely knew of the cable’s existence due to his familiarity with the area and frequent flights in the valley. However, the extreme heat and humidity may have contributed to fatigue or momentary distraction. The cables were visually indistinguishable from a distance against the landscape. Additionally, the helicopter was not equipped with a cable cutter device, which is not mandatory but could have mitigated damage.
The investigation highlighted systemic issues: obstacles exceeding 25 meters above ground outside densely populated areas should be integrated into obstacle charts. Furthermore, clearer mapping at a 1:50,000 scale would improve situational awareness for low-altitude operations.
Safety action
The STSB issued three recommendations to prevent similar accidents:
- Obstacles that are no longer in use should be removed.
- High-voltage lines located more than 25 meters above ground outside densely populated areas must be included in air navigation obstacle charts, treated like other cables.
- Air navigation obstacle charts should be published at a scale of 1:50,000 for greater clarity and utility to pilots.