In-flight fire caused by fuel leak in hot air balloon burner

Casualties unknown • Wakefield, Nelson latitude: 41° 19’ 60” S longitude: 173° 02’ 42” E, NZ

A fuel leak at the front left burner of a hot air balloon led to an in-flight fire, which escalated after the pilot failed to shut off the liquid fuel valves.

What happened

During a flight, the pilot noticed flames emerging from the front left burner of the balloon. While the fire was initially localized, it intensified quickly. The pilot attempted to manage the situation using fire extinguishers; however, because the liquid fuel valve on the fuel tanks and the pilot burners remained open, the leaking fuel continued to ignite near the adjacent burners. This caused the fire to re-ignite immediately after the extinguishers were used, leading to a larger, more uncontrollable blaze. Although the pilot's MAYDAY call lacked a specific last known location, emergency services were able to respond without delay.

The investigation

Investigators examined the burner components to identify the origin of the leak. While the fire's intensity prevented a conclusive determination of the exact source, the location of the flames ruled out connections at the fuel tanks. The investigation focused on the pressurized components between the tanks and the burner, specifically the liquid fire valve, the main ball valve, or the threaded connection between the liquid fire valve and the main valve block. Investigators noted that the direction of the flames was consistent with a failure at the connection between the liquid fire valve and the main valve block. It was suggested that over-torquing or cross-threading during installation, or subsequent damage from thermal cycling, could have created a crack. Furthermore, while the initial leak may have been small, the sustained heat likely caused secondary failures in seals and joint sealants, contributing to the outward spread of the flames.

Findings

A fuel leak at the front left burner was the primary driver of the fire.
The pilot's failure to shut off the liquid fuel valve and the pilot burners prevented the fire from being contained.
The pilot's clothing did not meet recommended industry standards for personal protective equipment, which increased the risk of injury.
Additional protective clothing was present on board but was not stored in a location that allowed for quick access during the emergency.
The use of a 90-degree valve on the liquid fuel outlet was identified as a potential safety improvement to help pilots recognize valve positions and improve fire survivability.

Probable cause

A fuel leak occurred at the front left burner, likely originating from a pressurized component such as the main ball valve or its connection to the liquid fire valve. The fire escalated because the liquid fuel and pilot burner valves were not closed, and the pilot's lack of appropriate protective clothing increased the risk of injury.

Frequently asked questions

What happened in the 2019-02-17 Airbus Helicopters AS350 FX2: SN: 1654 accident near Wakefield, Nelson latitude: 41° 19’ 60” S longitude: 173° 02’ 42” E, NZ?

A fuel leak at the front left burner of a hot air balloon led to an in-flight fire, which escalated after the pilot failed to shut off the liquid fuel valves.

What aircraft was involved and where did it happen?

The accident on 2019-02-17 involved a Airbus Helicopters AS350 FX2: SN: 1654, registration ZK-HEX, operated by Reid Helicopters Nelson, at Wakefield, Nelson latitude: 41° 19’ 60” S longitude: 173° 02’ 42” E, NZ.

What was the probable cause of the accident?

A fuel leak occurred at the front left burner, likely originating from a pressurized component such as the main ball valve or its connection to the liquid fire valve. The fire escalated because the liquid fuel and pilot burner valves were not closed, and the pilot's lack of appropriate protective clothing increased…

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