What happened
On the morning of 1 April 1997, a Cameron O-160 hot air balloon, registration ZK-FBS, was conducting a scenic passenger flight near Waimauku, Auckland. The flight, which included eight passengers, initially proceeded under clear conditions. However, as the balloon moved toward the Waimauku area, the aircraft entered a layer of fog that obscured the ground.
While attempting to land at a potential site, the pilot encountered a local wind shift that pushed the balloon toward State Highway 16. To avoid the roadside power lines, the pilot initiated a go-around maneuver. During this attempt to climb away, the bottom of the balloon basket made contact with a high-tension power line. The impact caused one of the six conductors to be pulled from its insulator and dragged for several spans before falling onto the road, resulting in a temporary local power outage. There were no injuries to the passengers or crew, and the aircraft sustained no damage.
The investigation
Investigators examined the sequence of events leading to the contact, focusing on the pilot's decision-making and the aircraft's performance. The investigation established that the flight duration had been extended because fog prevented an earlier landing. As the pilot descended into the fog, a south-east wind shift altered the balloon's track toward the hazard.
Technical analysis of the fuel system revealed that the heat output from the burners may have been compromised. At the time of the maneuver, the pilot was using fuel tanks that were nearly depleted. Because the residual pressure in tanks with low fuel levels decreases, the flow of liquid LPG was reduced, limiting the heat available to arrest the descent. Additionally, the investigation looked into the pilot's perceived fuel urgency, noting that while the pilot was concerned about remaining endurance, the actual fuel levels were higher than estimated.
Findings
- The necessity of a go-around was caused by a wind shift during a landing approach in foggy conditions.
- The go-around manoeuvre was insufficient or too late to prevent the basket from striking the power line.
- Reduced fuel pressure in the active tanks likely limited the heat output necessary for a successful climb.
- The pilot's concern regarding remaining fuel endurance may have influenced the decision to persist with the landing approach.
- The lack of available Whenuapai weather information for pre-flight briefings was noted, though it was not a factor in this specific incident.
Safety action
Following the investigation, recommendations were made to the Director of Civil Aviation to reinstate the supply of Whenuapai and Ohakea weather information for pre-flight briefings through the National Briefing Office. Furthermore, a system was recommended to monitor the ongoing adequacy and availability of weather information for general aviation.