What happened
On 5 August 2000, a Lindstrand LBL 105A hot air balloon, registration G-BUZJ, was conducting a public transport flight near Bristol Airport. The balloon had departed from Ashton Court earlier that morning with a crew of one and three passengers. During the flight, the pilot reported his position to Bristol Air Traffic Control, stating he was on the extended centreline of Runway 2 and approximately 5 km east of the airfield.
At 0609 hours, an Airbus A310 was on an ILS approach to Runway 27. As the heavy aircraft crossed over the balloon at 1,300 feet amsl, the balloon was at an altitude of approximately 500 feet amsl. Shortly after the aircraft passed, the balloon experienced a severe atmospheric disturbance. The envelope was violently forced downwards, causing the basket to tilt to 30 degrees, and subsequently swung upwards with enough force to throw the occupants to the floor. The pilot was unable to direct the burner flame into the mouth of the envelope due to the turbulence. To regain control, the pilot had to burn through the envelope material to allow air to re-enter. Following the incident, the pilot declared a PAN emergency and performed a gentle landing in a field. The three passengers sustained minor injuries.
The investigation
The investigation examined the flight paths of both the balloon and the Airbus A310, as well as the communication between the pilot and Air Traffic Control. Investigators noted that while the A310 pilots were aware of balloons in the area, they did not visually identify G-BUZJ during their approach.
Analysis of the position reports revealed a discrepancy in distance units. While aeronautical standards require the use of nautical miles, the balloon pilot had used kilometres, leading to a misunderstanding regarding his exact distance from the airfield. Furthermore, the investigation looked into the separation standards for wake turbulence, noting that while there are specific minima for aircraft following 'Heavy' category planes, there are no published separation minima for balloons.
Findings
- The primary cause of the upset was the encounter with the wake vortex generated by the Airbus A310.
- The atmospheric conditions present—light winds and stable air—were highly conducive to the persistence of wake vortices.
- The pilot's position report used kilometres instead of nautical miles, which affected the controller's assessment of the balloon's proximity to the runway centreline.
- There were no established separation requirements for balloons regarding wake turbulence from heavy aircraft.