What happened
On 28 February 2004, a Cameron Z-105 hot air balloon, registration G-BZVU, was conducting a passenger flight near Glastonbury, Somerset. The flight, which began at Ashton Court, had been underway for approximately 75 minutes when the pilot identified a suitable landing site in a field north of Glastonbury.
During the initial approach to the selected farmland, the pilot observed livestock in the field and subsequently aborted the descent to level the aircraft. Upon re-evaluating the approach, the pilot identified 33Kv power cables crossing the field. Although the pilot determined the cables were at a sufficient distance to avoid contact, the landing was resumed.
Upon touchdown, the wind speed at ground level was significantly higher than the pilot had anticipated. As the balloon began to deflate, the envelope experienced a 'spinnaker effect,' causing it to catch the wind and drag the basket toward the power lines. The deflating envelope eventually made contact with the 33Kv cables, causing a short circuit characterized by a visible flash and audible pop. There were no injuries to the one crew member or the four passengers on board. Following the incident, the passengers were evacuated to an upwind position, and the envelope was later found to have several burn holes caused by the electrical contact.
The investigation
The investigation examined the weather conditions, the pilot's decision-making regarding the landing site, and the physical mechanics of the balloon's movement during deflation. Investigators reviewed the pilot's assessment of the distance to the power lines and the discrepancy between the predicted wind speed and the actual wind speed experienced at ground level. The inspection of the G-BZVU envelope confirmed that the electrical discharge from the power lines had caused thermal damage to the fabric.