What happened
On December 8, 2008, an Ultramagic UM N-180 hot air balloon, registration HB-BUW, was preparing for a private flight near Berneck, Switzerland. The pilot selected a launch site near a farm, approximately 117 meters from a 20 kV high-voltage power line. While the pilot assessed the wind as light, atmospheric conditions suggested a temperature inversion was present.
During the inflation and takeoff phase, the balloon began to move due to the wind, eventually making contact with the chase vehicle. This movement caused the basket to rotate, creating asymmetrical tension on the lines of a quick-release system. The attachment lines snapped, causing the balloon to descend. In an attempt to stabilize the altitude and prevent a collision, the pilot activated both burners and even utilized a fast-deflating system to drop altitude quickly. However, the balloon's momentum carried it toward the power lines. The burner frame struck the 20 kV lines, triggering short circuits that severed the envelope lines and caused the basket to fall from a height of approximately 7 to 8 meters. The impact caused a fire in the basket due to a ruptured gas line, though the pilot managed to close the gas valves to extinguish the flames.
The investigation
SUST examined the technical state of the HB-BUW, the meteorological conditions at the time of the accident, and the operational decisions made by the crew. The investigation focused on the stability of the launch site, the functionality of the equipment, and the timing of the pilot's emergency maneuvers. Investigators also reviewed the pilot's qualifications and the weather forecasts used to plan the flight.
Findings
- The primary cause of the accident was the collision with a 20 kV power line resulting from the choice of a launch site that was inherently risky under the prevailing meteorological conditions.
- The installation of an uncertified quick-release system on the basket contributed to the accident, as the attachment lines were not sufficiently strong to withstand the tension.
- The decision to abort the takeoff was made too late to prevent the impact with the electrical infrastructure.
- A temperature inversion in the lower atmosphere influenced the flight path and local wind conditions.
- The collision caused two serious injuries and one light injury among the occupants, along with significant damage to the balloon, the power lines, and the chase vehicle.