Ageing Hercules and Orion Air Force planes are proving costly for the Defence Force.
A NZ Air Force P-3 Orion Photo: supplied NZDF
The Defence Force has spent around $360 million on maintenance and repairs over the past 10 years, twice as much as in the previous decade, official figures show.
In 2008, keeping the planes fit for purpose cost about $24m. Two years ago the cost spiked over $50m, and this year the bill is more than $43m.
Defence bought its five Hercules and six Orions in the 1960s and all are coming to the end of their operational lives.
Official documents show the Orions had five engine failures over 15 days last year because of propeller malfunctions.
The Hercules also had propeller leaks and faulty oil gauges.
Replacing the aircraft would be costly and Defence Minister Ron Mark has accused the previous government of putting off the decision.
David Capie from the Centre for Strategic Studies at Victoria University said successive governments had known that the capabilities needed to be replaced and updated.
"But the replacements are all so expensive - an eyewatering amount of money - so I think there has been a tendency to think that this is a can that can be kicked down the road," he said.
Documents released under the Official Information Act reinforce the risk of keeping the old fleet.
The papers said: "The operation of aircraft that are in excess of 50 years old will result in an increase in unexpected maintenance action. This comes at an increasing cost to support through obsolescence and increased risk to mission success."
National had promised a $20 billion upgrade of the armed forces - but when Mr Mark took charge of the Defence portfolio last year he said there was no hard cash to back that up.
Mr Mark has criticised National for the failure to get new equipment, but National's defence spokesperson Mark Mitchell said the moves were under way to replace the old Orions with Boeing P8 Poseidon aircraft when his party was in power.
"The fact of the matter is as the minister I already had the process well underway in terms of the procurement on the P8s.
"It's actually this government and this minister that's kicking the can down the road.
"They should have made a decision at least by April or May this year," he said.
He said Mr Mark had put on the brakes by launching a number of reviews.
David Capie said Defence was a portfolio that was highly political and not necessarily a vote winner.
"Most New Zealand political parties probably calculate there's not a lot of votes in the lead-up to elections that can be made in the defence sector but at somepoint there needs to be some hard decisions made about replacing and investing in these capabilities."
Mr Mark said he would have to make a decision before the end of July whether to replace the Orions with the Boeing P8 Poseidon.
In the meantime, he said officials had reassured him the old planes were safe to fly.