What happened
On August 11, 2001, a Thunder & Colt/ Colt 105 A hot air balloon was conducting a promotional flight near the Bleilochtalsperre reservoir during a large public event. To avoid wind issues, the pilot chose to launch from a location approximately two kilometers west of the reservoir rather than the designated event site.
During the flight, the balloon traveled at a very low altitude, crossing a forested area and the surface of the reservoir. While flying at an altitude of less than 20 meters, the balloon passed over the water and approached a campsite. As the balloon reached the campsite, it was flying at an altitude of only 3 to 5 meters. In an attempt to climb, the pilot engaged the burner to ascend, but the basket struck a 20-kV overhead power line.
The contact with the lines caused an electric arc, which short-circuited the phases and through-welded two of the basket's load-bearing cables. This caused the basket to tilt forward, resulting in the pilot falling approximately 10 meters to the ground. The balloon continued to fly at an altitude of about 200 meters for roughly one kilometer before landing in a tree. The passengers were able to exit the basket safely, though the aircraft sustained heavy damage from the collision and subsequent fire.
The investigation
The BFU investigation focused on the flight sequence, the aircraft's airworthiness, and the operational conditions. Investigators examined the pilot's authorization, the aircraft's maintenance records, and the load configuration. The investigation noted that while the pilot was experienced and authorized to fly, several regulatory discrepancies were identified. Specifically, the aircraft was carrying four passengers, which exceeded its approved capacity for commercial transport. Additionally, the investigation found that three of the four gas cylinders on board lacked valid safety inspections, and the aircraft was loaded at the limit of its maximum takeoff weight for the ambient temperature.
Findings
- The pilot failed to identify the overhead power line in a timely manner while flying at a dangerously low altitude.
- The maneuvers performed to avoid the obstacle were ineffective.
- The aircraft was operating with an excessive passenger load for its approved configuration.
- Several gas cylinders used during the flight lacked valid proof of safety inspections.
- The aircraft was operating at the edge of its maximum allowable takeoff weight for the prevailing temperature.
- The pilot was flying below the required minimum safety altitude.