What happened
On June 4, 2013, at approximately 14:00, an Eurocopter AS350B3, registration F-GSOE, was conducting an aerial photography and filming mission for EDF near Livet-et-Gavet. The pilot, accompanied by three passengers, had departed from Grenoble Le Versoud airfield earlier that afternoon to document high-voltage power lines.
After completing tasks at two previous sites, the pilot proceeded to a third location. While performing a 360-degree right-hand turn directly above a mountain tunnel exit, the main rotor blades struck a high-voltage line. The impact caused the engine to fail and induced significant vibrations. The pilot managed to execute an emergency landing in a nearby clear area. During the engine shutdown, the aircraft experienced transient ground resonance, prompting the pilot to apply the rotor brake.
The investigation
The investigation established that the pilot had participated in a safety meeting in April 2013 to prepare for the mission and identify potential obstacles. Additionally, a reconnaissance flight had been conducted the day before the accident. The high-voltage line in question had been previously identified during these preparations.
However, the specific line struck during the accident was situated along a very steep mountainside, suspended between a pylon at the mountain summit and another in the valley. The investigation noted that this particular line is extremely difficult to detect visually. On the day of the accident, the pilot believed the aircraft was at a higher altitude than it actually was and failed to see the wires.
Findings
- The primary cause of the accident was the pilot's failure to detect the obstacle on the flight path.
- This failure was likely due to a decrease in vigilance following more than one hour of flight operations.
- The pilot's focus on the filming objectives located below the aircraft may have contributed to a reduction in situational awareness regarding the flight path.