What happened
On 1 January 2011, a Cameron O-120 hot air balloon, registration G-BVX and XF, was conducting a private flight near Midsomer Norton, Somerset. The pilot was attempting to achieve a 'Gold Badge' flight by reaching an altitude of 6,000 metres (approximately 19,700 ft). After successfully climbing to 21,500 ft, the aircraft began a controlled descent. However, following a brief period of stable descent, the balloon entered a rapid, uncontrolled fall at approximately 5,500 ft/min. Witnesses observed the envelope in a collapsed, 'streamered' state as it descended vertically. The balloon struck a bowling green, where an intense post-impact fire ensued. Both the pilot and the passenger sustained fatal injuries.
The investigation
AAIB investigators examined the wreckage and analyzed radar data. The investigation focused on the transition from a steady descent to the rapid fall. Radar tracks confirmed the aircraft reached its peak altitude before the sudden loss of lift. Examination of the envelope showed no evidence of structural failure or significant tears that would have caused an in-flight breakup. The investigation also looked into the use of the 'lock top' deflation system, a modified parachute valve. While the pilot was familiar with the system, this was his first flight using this specific configuration. Additionally, the investigation reviewed the supplementary oxygen system, noting that the valves were found in the closed position, and evaluated the potential impact of hypoxia on the crew's decision-making at high altitudes.
Findings
- The accident likely resulted from a combination of factors, including a mishandled parachute valve, the pilot's inexperience with the lock top system, and the unique handling characteristics of a large balloon operating at a low mass and high rate of climb.
- There was a possibility that the pilot initiated a rapid descent to avoid exceeding approved flight levels, potentially leading to the envelope's collapse.
- The crew's performance may have been degraded by hypoxia, as the flight reached altitudes where oxygen levels are significantly reduced.
- The post-impact fire, likely ignited by the burners, was the cause of death for the passenger.