The Defence Force plane the prime minister was travelling on is unlikely to be fixed in time make it to Japan to fly him and his trade delegation home, Defence Minister Judith Collins says.
Christopher Luxon had to leave most of his delegation behind in Papua New Guinea when the plane broke down.
Collins told Morning Report the back-up Defence Force plane is in long-term maintenance and would not be free until the end of next month.
Replacing the fleet would cost hundreds of millions of dollars, and that would be have to weighed up against the current economic climate.
Prime Minister Christopher Luxon in Papua New Guinea. Photo: Nathan McKinnon
Luxon was only supposed to be in Port Moresby for 90 minutes on Sunday while the Boeing 757 was refuelled.
After an hour's delay, a Defence Force spokesperson confirmed the aircraft had blown two fuses, forcing the prime minister to take a commercial flight.
The accompanying trade delegation stayed behind in Papua New Guinea on Sunday night, and flew out on Monday to Brisbane, from where they would take an Air NZ flight to Tokyo.
Collins said spoilers had to be taken off the plane's wings, which meant it could not fly at high enough altitudes for long haul flights.
"We shouldn't count on it getting to Japan to bring back the prime minister and his delegation - unless a miracle happens and suddenly it's fixed."
The Defence Force had done everything it could, she said.
"The Defence Force has done an amazing job keeping aircraft that would otherwise ... in better times be retired quite quickly."
Defence Minister Judith Collins says the back-up Defence Force plane is in long-term maintenance. Photo: RNZ / Samuel Rillstone
"It's much better if we have a backup plane available - it's like in any airline there's always issues with planes.
"These are very old planes, they're over 23-years-old. These would normally not be used commercially now at this stage."
The Defence Force capability review, which had been had been brought forward from September to June, would look at the issue of planes.
"New planes will have to be weighed up against the current economic climate and the fact that we've got so many families who are facing challenges", she said.
"It's a hell of a lot of money."
Collins would not give an exact cost but said it would be "hundreds of millions of dollars", though there were options for leasing and chartering.
Earlier this year, Luxon was also forced to take a commercial flight to Melbourne, when a Defence Force plane broke down before leaving the tarmac in Wellington.
