What happened
On the evening of September 26, 2003, a Cameron Balloons O 105 hot air balloon, registered F-GMMD, was conducting a short local flight with a pilot and two passengers. During the flight, the pilot maintained an altitude of approximately 150 meters. As the aircraft approached the landing site, the pilot attempted to contact the ground chase vehicle via mobile phone because the low altitude prevented radio communication with the vehicle, which had drifted away from the balloon's trajectory.
While the pilot was preoccupied with the telephone conversation, the balloon descended toward the ground. The pilot believed the flight path was clear of obstacles; however, as the balloon neared the surface, a medium-voltage power line became visible directly in the flight path. In an attempt to regain altitude and avoid the wires, the pilot needed to increase heat. However, the active gas cylinder was nearly empty and could no longer provide sufficient heat for the double burner. The pilot attempted to switch to a full cylinder, but the time required to close the empty valve and open the new one meant that sufficient lift could not be generated in time to clear the obstacle.
In a final effort to avoid the lines, the pilot opened the valve fully, but the balloon was forced into the ground. The balloon's envelope made contact with the power lines and subsequently caught fire. The pilot and passengers successfully evacuated the basket and managed to detach it from the envelope to prevent the basket from also catching fire.
The investigation
Investigators examined the sequence of events leading to the impact and the state of the aircraft's equipment. The investigation established that the visibility of the power line pylons was compromised: one pylon was obscured by vegetation, while the other was hidden from the pilot's view by the basket itself during the final approach. The investigation also confirmed that all four gas cylinders were full at the time of takeoff, but the depletion of the active cylinder necessitated a manual changeover during a critical phase of flight.