What happened
On the morning of May 21, 2010, a Linstrand Balloons 330 A hot air balloon, registration F-HDRT, was conducting a commercial sightseeing flight near Chissay, France. Shortly after takeoff, the balloon began rotating rapidly to the right around its vertical axis. The pilot identified that the right-side rotation ventail (flap) had become stuck in the open position.
In an attempt to stabilize the flight, the pilot manipulated the ventail controls, though they avoided excessive force to prevent damage to the envelope. The pilot then opened the left-side ventail to counteract the rotation. To maintain clearance from nearby obstacles, the pilot continued to heat the envelope. Upon identifying a suitable landing field, the pilot notified the 16 passengers of the necessity for an emergency landing and instructed them on how to position themselves within the basket. The subsequent landing was hard, resulting in four passengers sustaining injuries, including one serious injury.
The investigation
Investigators examined the balloon's control systems, including the cables and pulleys, after the envelope had been partially reinflated. The inspection revealed no signs of wear or mechanical fatigue that would explain the ventail sticking open. Two potential scenarios were considered regarding the malfunction:
- The control cable, which features an aramid core and polyester sheath, is relatively rigid and prone to forming loops. If such a loop enters a pulley groove, the control mechanism can jam.
- The control line may have become entangled with secondary lines connected to the ventail fabric, effectively shortening the line and preventing the ventail from closing properly.
While the pilot had inspected the controls during the inflation process, investigators noted that the heating of the envelope can cause lines to tangle or loops to form after the initial ground checks are completed. Furthermore, while the pilot did not perform functional tests of the ventail movement prior to takeoff, the flight manual at the time did not explicitly require these specific tests.
Findings
- The primary cause of the uncontrolled rotation was the incomplete verification of the control system's functionality prior to takeoff.
- The mechanical failure was likely due to the control cable becoming jammed in a pulley or becoming entangled with secondary lines during the heating process.
- The flight manual lacked specific instructions for performing functional ventail tests before departure.