What happened
On April 10, 2008, a Cameron Ballons Z 150 hot air balloon, registration F-GTET, was conducting a passenger flight over the Nieppe forest near Vieux-Berquin, France. During the flight, the commander requested that the second pilot take responsibility for managing the burners. Shortly after, the second pilot accidentally closed the pilot light valve on one of the two burners while attempting to adjust the main valve.
As the crew began their descent, the second pilot attempted to use the silent burners to avoid disturbing wildlife below. During a 18able-degree rotation of the basket, the pilot's orientation relative to the controls changed. While attempting to control the descent rate at approximately 80 meters above the tree canopy, the second pilot accidentally closed the pilot light valve on the right burner. In an attempt to relight it, the pilot inadvertently closed the pilot light valve on the left burner as well.
Efforts to relight the burners using the onboard piezo-electric igniter failed. The crew attempted to use an emergency lighter, but it was ineffective. Furthermore, the emergency gas lighter was lost in the bottom of the basket and could not be located. Realizing the loss of heat, the crew notified the passengers to prepare for a hard landing. The balloon struck trees before bouncing approximately ten meters off the ground and coming to a rest in a logging path.
The investigation
The investigation focused on the mechanical operation of the Cameron MK4 double burner and the crew's operational procedures. Investigators noted that the pilot light valves and the silent burner valves were identical in shape and size, which contributed to the error.
It was established that the second pilot was performing a supervised flight intended to familiarize him with the company's equipment. However, the pilot had no prior experience with this specific burner model, having previously flown aircraft with different control layouts. Additionally, the investigation found that no pre-flight briefing regarding the specific equipment was conducted by the commander, and the crew had failed to verify the location of the emergency lighting system prior to takeoff.