What happened
On January 15, 2008, a Cameron Z 120 hot air balloon, registration F-GVJO, was participating in a scheduled aerial event near Praz-sur-Arly. The flight, operated by a local tourism office, initially proceeded as planned, with the pilot navigating toward Megève and later toward Sallanches. During the flight, the pilot encountered turbulence caused by the onset of Foehn wind conditions and subsequently decided to terminate the flight and land in a meadow north of Sallanches.
As the balloon approached the landing site at approximately 10:30 local time, the pilot attempted to land behind a grove of trees to seek shelter from the wind. While descending at approximately ten knots, the balloon's trajectory drifted left, bringing the aircraft into close proximity with a 20,000-volt power line located roughly 300 meters away. In an attempt to clear the obstacle, the pilot activated both burners to increase altitude. However, the basket struck the electrical line, triggering an immediate fire.
Following the impact, the pilot maneuvered the balloon to avoid hitting nearby railway catenary wires. To prevent further collision, the pilot performed a heavy vent of the envelope, resulting in a hard landing between a railway line and a highway. The basket tipped onto its side, and while the occupants managed to evacuate, the intense heat caused the remaining propane cylinders to explode, destroying the aircraft.
The investigation
The investigation focused on the sequence of events leading to the contact with the electrical infrastructure and the subsequent fire. Investigators examined the impact of the 20,000-volt line on the aircraft's equipment and the behavior of the fuel cylinders. The inquiry established that an electrical arc had pierced the wall of one propane cylinder through its thermal insulation. This perforation allowed pressurized gas to escape, fueling a large external flame. The heat from this initial fire was sufficient to cause the explosion of the four remaining cylinders upon landing.
Findings
- The primary cause of the accident was the late perception of the power line obstacle during the landing phase.
- The pilot's decision to execute a go-around (increasing heat to clear the obstacle) contributed to the collision.
- The impact with the high-voltage line created an electrical arc that compromised the integrity of a propane cylinder.
- The resulting fire and subsequent explosion of all fuel cylinders led to the total destruction of the Cameron Z 120.
- The accident resulted in 3 injuries (the pilot and two passengers).