Hikers in Kosciuszko National Park over the past week would have been treated to an unusual aerial display if they happened to be near Possum Point.

They might have spotted a small fixed-wing plane eject a puff of smoke, signalling to a hulking Boeing 737 trailing less than half a kilometre behind just where to dump its load of water, gel or fire retardant on the uncontrolled bushfire below.

John Gallaher, a US pilot, at the controls of a Boeing 737 converted into an air tanker to fight fires for the NSW Rural Fire Service and other agencies. Credit:NSW RFS

"We talk to the 'bird dog', and they give us a description of the fire," said John Gallaher, one of two pilots behind the controls of the converted jetliner. "We get the target and tuck in behind."

At their lowest, the 737's sorties are just 150 feet (45 metres) above the vegetation, the US pilot said, adding somewhat nonchalantly: "It's the same pattern as when you land at the airport [except] you go around and do it again."