What happened
On May 13, 2012, a G34/24 hot air balloon, registration F-HTML, departed from Essomes-sur-Marne for a sightseeing flight intended to reach Saint-Siméon. Shortly after takeoff, the balloon crossed a ridge featuring 120-meter wind turbines and descended to a very low altitude.
Approximately 18 minutes into the flight, while overflying a vineyard near Charly-sur-Marne, the balloon struck a medium-voltage electrical line (20,000 volts) positioned 8 to 10 meters above the ground. The contact caused electrical arcs between the cables, leading to a violent fire near the burner assembly. An occupant attempted to use an onboard extinguisher but was unable to suppress the flames. The occupant eventually jumped from the basket to evacuate.
Following the impact, two load-bearing cables snapped due to heat, causing the basket to tilt and the three remaining occupants, along with the three gas cylinders, to fall to the ground. The partially deflated envelope continued to drift for 6 km, eventually snagging on telephone and electrical wires in Saacy-sur-Marne. The accident resulted in 3 fatalities and 1 injury.
The investigation
The investigation focused on the flight path, the mechanical state of the aircraft, and the pilot's actions. Investigators examined the wreckage and found no evidence of prior mechanical malfunction. Analysis of the electrical lines showed that two cables had ruptured due to fusion from short-circuiting. The investigation also noted that one gas supply hose had partially ruptured, likely due to heat.
GPS data from the onboard Flytec calculator revealed that the flight was being conducted at an average altitude of less to than 100 meters after passing the wind turbines, with recent flights in May averaging below 50 meters. The pilot, who had earned his hot air balloon license in February 2012, had accumulated 47 total flight hours.
Findings
- The pilot detected the power lines only after being alerted by a passenger.
- The primary cause of the accident was the execution of a low-altitude flight and the late detection of the power lines by the pilot.
- The decision to attempt to climb over the lines rather than performing an immediate emergency landing contributed to the severity of the accident.
- The low altitude of the flight (under 100 meters) significantly reduced the margin for error when obstacles were encountered.