What happened
On Monday, October 22, 2001, at approximately 13:30, a Bell 47 G helicopter, registration F-GGSU, was conducting a low-altitude agricultural pest reconnaissance mission in the Doubs valley near Soulce-មានCernay. The flight was operated by an air charter company, carrying the pilot and one passenger.
While flying at a very low altitude to identify vole activity, the helicopter's main rotor blades struck a high-voltage power line spanning the valley from east to west. The impact caused the aircraft to lose stability, leading to a crash that resulted in a post-impact fire. The collision caused the destruction of the aircraft and damaged the electrical infrastructure. The accident resulted in two fatalities, involving both the pilot and the passenger.
The investigation
The investigation focused on the visibility of the obstacle and the operational conditions of the flight. Investigators determined that the power line was not marked and lacked sufficient contrast with the surrounding environment to be easily identified. At the time of the accident, the aircraft was flying roughly toward the sun, which further complicated visual identification. Additionally, analysis of the cockpit bubble revealed significant cracking, suggesting the material was aged and potentially degraded the pilot's field of view.
Regarding navigation, the pilot was using a 1/500,000 scale ICAO chart. While this map noted a power line two kilometers south of the accident site, the specific line involved in the collision was not depicted. The chart's legend explicitly stated that certain obstacles might not be represented.
Furthermore, the investigation examined the pilot's authorization for low-altitude flight. While the pilot held a specific derogation allowing for low-level operations for tasks such as aerial photography and pipeline monitoring, the investigation found that agricultural pest reconnaissance was not explicitly covered by this authorization. Such missions require extremely low speeds and altitudes, often involving non-standard flight paths and high levels of concentration on the ground, which limits the pilot's ability to anticipate obstacles.
Findings
- The primary cause of the accident was the failure to perceive the power line obstacle.
- Environmental factors, including the sun's position and the lack of contrast between the unmarked line and the landscape, contributed to the collision.
- The aged and cracked condition of the aircraft's canopy likely hindered visibility.
- The specific nature of the pest reconnaissance mission—requiring intense focus on the ground—increased the difficulty of obstacle avoidance.
- The pilot's existing flight derogations did not explicitly encompass the specific type of low-altitude activity being performed.