What happened
On June 13, 1980, at approximately 09:15 local time, an OH13H Mk 6 B "Tomcat" (registration HB-XFU) was performing agricultural spraying operations over a vineyard near Sion, Switzerland. The aircraft, operated by Trans-Héli S.A., was applying chemical treatments to a plot belonging to the Valais Cantonal Agricultural School.
During the final pass of the mission, the pilot attempted to increase altitude by activating the rapid discharge valves to lighten the aircraft. Witnesses observed the pilot waving to onlookers just before the aircraft encountered an electrical line crossing the flight path. The right-side spreading bar struck two of the upper conductors of the power line, causing the helicopter to lose control and crash into an adjacent field. The pilot was transported to a hospital in Sion but succumbed to his injuries the following day.
The investigation
The investigation focused on the mechanical state of the aircraft and the pilot's actions during the final maneuver. Investigators examined the wreckage and found no evidence of mechanical failure; the engine, flight controls, and anti-torque systems were all fully functional at the time of the accident. Traces of short-circuiting were discovered on the right spreading bar and its support, confirming the contact with the electrical wires.
Medical examinations revealed that the pilot died from brain injuries sustained during the impact, likely caused by striking the door frame. The investigation also noted that while the vineyard was marked, the electrical line was not, although a nearby utility pole was marked with a yellow flag.
Findings
- The primary cause of the accident was a collision with an electrical line caused by a lack of attention by the pilot at the conclusion of the mission.
- The pilot's focus appeared to have lapsed during the final stages of the task, as evidenced by his interaction with bystanders and the sudden attempt to lighten the load just as the obstacle was encountered.
- The pilot had completed specialized spraying training in Germany but had proceeded to fly autonomously without the intended period of supervised flight.
- The absence of a protective helmet significantly contributed to the fatal outcome, as the impact injuries might have been survivable had the head been protected.
Safety action
- The investigation raised a recommendation to consider mandating the use of protective helmets for occupants during aerial work operations to increase survival rates during accidents.