A former Defence Minister says the price tag for a couple of new Air Force planes would be at least a couple hundred-million-dollars.

The Prime Minister's Air Force Boeing 757 was meant to fly out this morning, but a technical fault with the nose landing gear meant the aircraft's been grounded all day.

Chris Luxon was forced to fly commercial to Melbourne for ASEAN talks.

Wayne Mapp says the planes are for more than just flying the Prime Minister around.

"We use them for troop transport, cargo round the Pacific, and also going down to Antarctica."

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