What happened
On July 15, 2004, at approximately 17:20, a LAK 17 A glider, registration HB-3366, was participating in a speed trial as part of the 2004 World Mountain Soaring Cup. The flight was part of a 500 km circuit between Vinon and Sallanches.
Witnesses reported that the aircraft was flying at a very low altitude near the Dent du Burgin rock face, heading toward the Saulire summit. While maneuvering close to the cliffside, the glider's right wing struck a Catex cable—a line used for transporting explosives. The impact caused the aircraft to crash into a rocky area just below the cable at an altitude of approximately 2,400 meters. The accident resulted in the death of the pilot and the total destruction of the aircraft.
The investigation
Investigators examined the wreckage and identified significant damage to the right wing, specifically noting that a 2.5-meter section of the leading edge had been torn away. Despite this damage, the flight controls remained functional.
Analysis of the site revealed that the cable, which had a diameter of 7.5 mm, was positioned roughly 30 meters above the ground at the point of impact. The investigators noted that the cable was difficult to see. Furthermore, the surrounding rocky terrain and the nature of the support pylons provided very little visual contrast for a pilot flying at such low altitudes. The investigation also considered the lighting conditions, noting that the pilot had the sun positioned within a 5-degree arc of their field of view when facing the Dent du Burgin.
Findings
- The primary cause of the accident was the failure to perceive the obstacle.
- The 7.5 mm diameter cable was highly difficult to detect due to its low visibility and the lack of contrast between the support pylons and the mountainous environment.
- The pilot was operating at a very low altitude near a steep rock face, which increased the difficulty of spotting thin obstructions.
- Environmental factors, including the sun's position, may have contributed to the difficulty in identifying the cable.