Christopher Luxon would look at commercial options over 'ancient' Air Force planes that 'shouldn't be flying' if PM

National leader Christopher Luxon says he would explore commercial arrangements if travelling overseas as Prime Minister rather than taking the "ancient" Air Force planes.

The breakdown-prone Defence Force Boeing 757 planes are back in the spotlight after it emerged on Monday a backup aircraft went on Prime Minister Chris Hipkins' latest overseas trip in case the main one broke down.

The second plane hasn't flown the whole way to Beijing but instead travelled to Manila in the Philippines, and is now waiting in Darwin to provide support on the Prime Minister's return trip.

A spokesperson for the Prime Minister said it isn't unusual for the Air Force to provide backup aircraft - it's something that's happened frequently since multiple highly-publicised breakdowns in 2016, and it's a decision made by the Air Force.

The planes are about 30 years old and aren't due to be replaced until about 2028-2030.

The revelation that a second plane was overseas led to criticism from National and ACT, with the latter calling it an example of Labour's "wasteful attitude" and a "national embarrassment" New Zealand's fleet was so out-of-date.

Speaking to reporters on Tuesday morning, Luxon, the National leader and former Air New Zealand chief executive, said the current planes are "unreliable" but it would be "inappropriate" to commit to purchasing new planes during a recession.

"My personal view is you travel commercial," he said.

It was put to Luxon the Air Force plane is taking a large delegation.

"There are a whole bunch of options, you know, commercial travel, charter travel, there's a whole range of other options available to the New Zealand Government.

"If you're on one of those trading delegations, as I was in the past, I never travelled on the 757 if possible because I could go direct flight in a much quicker way."

Luxon noted he and Hipkins flew commercially when flying to the King's Coronation in May.

"The reality for New Zealand is we have unreliable aircraft, we can't afford new ones in the middle of a recession. There are other priorities for New Zealand. 

"So, the reality, whether you like it or not is that we should be travelling commercially."

He called the current aircraft "ancient" and said, "they shouldn't be flying".

"They're well past their use-by date. We are now in a recession and this will not be a priority in my Government. 

"The reality is, whether you like it or not, we travel commercial, we charter aircraft, we do a whole bunch of other arrangements that are possible in order to do that."

In the statement on Monday, the Prime Minister's Office said using the Air Force planes "is far cheaper than a commercial charter and has other benefits such as security, and the ability to travel point to point to reduce time away from home and additional costs such as hotels which would be required if there were stopovers".

Data provided to ACT shows about $70 million was spent on the planes' maintenance and repairs between 2017 and mid-2022, and then a further $33 million since.

"The planes are breaking down more and costing more as time passes," ACT defence spokesperson Dr James McDowall said. "The reason we're stuck with these clunkers is because the Government is underinvesting in defence. 

"At the moment we're lucky to be able to successfully get off the tarmac let alone defend ourselves, our allies and our values in today’s increasingly volatile strategic environment," Dr McDowall said.

Luxon believed it would be cheaper to take commercial than continuously repairing the aircraft.

On AM on Tuesday morning, Acting Prime Minister Sepuloni said the previous Government had underfunded defence. 

"The $4 billion investment we've put in [to the Air Force] was on the back of nine years of a Government who barely invested anything… I think it might've been a couple of hundred million that they put into the Air Force, at that time."