What happened
On the morning of July 5, 2001, a Bell 47 G 2 helicopter, registered F-BIEI, was engaged in agricultural spraying operations near Dessenheim, France. The pilot had departed from Colmar Houssen earlier that morning to refuel and collect phytosanitary products. Prior to the flight, the pilot studied topographic maps provided by an agricultural cooperative to plan the day's mission, which involved treating several corn fields.
At approximately 10:10 AM, while working on the third field of the morning, the pilot began a reconnaissance pass to establish flight paths. The pilot intended to fly beneath a specific medium-voltage power line crossing the field. During the maneuver, while flying westward at the edge of the plot and initiating a turn, the helicopter struck another medium-voltage power line. The impact was severe enough to break several concrete utility poles and sever the electrical lines. The aircraft was caught by the cables, but the pilot managed to self-extricate from the wreckage. The accident resulted in one injury to the pilot and the total destruction of the aircraft.
The investigation
The investigation focused on the pilot's preparation and the visibility conditions at the time of the accident. Investigators examined the maps used by the pilot, noting that while high-voltage lines were documented, the specific medium-voltage line involved in the collision was not present on the studied charts. The investigation also looked into the pilot's recent flight history and the environmental conditions, including solar position and recent fatigue levels.
Findings
Several factors contributed to the collision:
- The pilot had an incomplete knowledge of the site, as the specific medium-voltage line was not identified during the initial aerial reconnaissance or through ground inspection.
- The pilot was distracted by the need to fly close to a utility pole to maximize clearance under the cables.
- Visual conditions were compromised by a "very bright and white" sun, which hindered the detection of the obstacle.
- Potential fatigue was a factor, as the pilot had completed a long duty day the previous evening, finishing work at 9:30 PM after 9.5 hours of flight time.