The 43-year-old was the only person on board and was trying to drop water on to a blaze near Ulladulla, south of Sydney, when his plane went down, Rural Fire Service commissioner Shane Fitzsimmons said.
Mr Fitzsimmons added: "He's a husband with young children and we're all acutely aware there's a family suffering because their dad hasn't come home.
"We're also feeling for the firefighting community as a whole."
More than 100 wildfires have killed one resident and destroyed more than 200 homes in New South Wales this month.
Sixty-one fires were burning, with 23 out of control, although cooler weather has decreased the fire threat and many residents who evacuated have returned to their homes.
Fire officials have defended Australia's defence department after investigators revealed a military training exercise with live ordnance ignited the largest of the wildfires.
The fire near the city of Lithgow, west of Sydney, has burned 180 square miles and destroyed several houses but caused no injuries or deaths.
Mr Fitzsimmons said the defence department's actions were obviously an accident.