What happened
On July 7, 2007, at 18:05, an Eurocopter AS350 B3 helicopter, registration D-HAUW, was conducting aerial surveillance for a cycling race in the mountainous region of Mont-de-Lans. The flight, operated for commercial purposes, involved the pilot and four observers. The mission required the crew to follow the race route at low altitude to monitor competitors.
While flying west at approximately 45 knots through a narrow valley, the pilot encountered high-voltage power lines. Due to the sun's position and the terrain, the pilot spotted the lines only at the last moment. During an evasive maneuver, the aircraft made contact with the wires. The impact caused a momentary failure of the Vehicle and Engine Multifunction Display (VEMD) and triggered an electrical arc between two active conductors, as confirmed by the power line operator. The pilot subsequently performed a precautionary landing at a nearby rest area. There were no fatalities or injuries.
The investigation
The investigation focused on the visibility of the obstacles and the pilot's situational awareness. Investigators found that the pylons and power lines were not marked, and they provided very little contrast against the surrounding environment. The pilot noted that a pylon on the right was largely obscured by vegetation, and a pylon on the left went unnoticed. Additionally, the pilot was flying directly toward the sun, and while wearing a helmet with a sun visor, visibility was compromised.
Physical evidence on the aircraft included scrape and burn marks on the rear skid, as well as evidence of an electrical arc on the left skid wear plates. The investigation also reviewed the pilot's recent flight history and operational context, noting that while the pilot was experienced in local aerial work, this specific type of mission—following a road race—was infrequent.
Findings
- The primary cause of the contact was the pilot's failure to perceive the power lines and the presence of an obstacle in the flight path.
- Environmental factors contributed to the incident, including the lack of marking on the power lines and the low visual contrast of the pylons against the landscape.
- The pilot's flight path was directly into the sun, which hindered the detection of the wires.
- The pilot admitted to forgetting the presence of the specific power line during this flight.
- The pilot reported experiencing fatigue and low motivation due to a heavy workload, having completed 5.5 hours of aerial work the previous day.