What happened
On December 8, 2009, at approximately 14:00, an Eurocopter AS 350 BA (registration F-GHBR) was conducting a low-altitude aerial survey along the Allier River near Lavoûte-Chilhac, France. The mission, performed for the benefit of a water and aquatic environment agency, involved flying at an altitude of approximately 50 meters to allow crew members to count salmon spawning grounds.
While flying at a low speed of approximately 20 knots, the helicopter struck a three-cable electrical line. The impact caused the cables to break. The pilot performed an immediate precautionary landing in a field adjacent to the river. Following the collision, the pilot contacted maintenance, inspected the aircraft, and subsequently flew to Issoire to disembark the three passengers before returning to the company base in Valence. The impact resulted in damage to the aircraft, specifically requiring the replacement of all three main rotor blades.
The investigation
The investigation focused on the flight preparation and the visibility of the obstacle. The pilot had utilized a 1/5/00,000 scale ICAO aeronautical chart for flight planning. This specific chart only displays high-voltage lines exceeding 225 kV or 150 feet in height; consequently, the power line involved in the accident was not depicted.
Investigators examined the documentation provided by the electricity network operator, ERDF. While ERDF's records did mention the presence and height of the line (50 meters above the riverbed), such detailed maps are typically only provided to aerial work companies when the operator is commissioning line surveillance.
Furthermore, the investigation reviewed the aerial work company's Operations Manual. At the time of the accident, the manual defined procedures for low-altitude flights and regulated airspace but did not specifically address the requirements for salmon spawning surveys, nor did it mandate the use of specialized maps for such tasks.
Findings
- The primary cause of the collision was the absence of precise documentation during flight preparation, which led to the failure to detect the electrical obstacle.
- The terrain and local vegetation at the site made the power lines difficult to detect visually.
- A contributing factor was the lack of a site reconnaissance flight prior to the mission.
- The aeronautical charts used by the pilot did not include the specific power line involved in the accident.