C130 Hercules have been key to the work of the Royal New Zealand Air Force, however the aging aircraft are increasingly having issues.

Emergency alerts for air force aircraft are on the rise at Whenuapai air base in Auckland.

At more than 50-years-old, the New Zealand Air Force's Hercules and Orions are well past upgrades, but both fleets would keep running until a decision on replacements was made later this year.

The aged C130 Hercules were likely to remain in service, with the defence minister making a recommendation to Cabinet to replace the air force's P3K Orions as a more immediate priority.

Professor Robert Ayson, from Victoria University's Centre for Strategic Studies, said successive governments have opted for refurbishments, but that could no longer be an option for either fleet.

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"It doesn't matter how well they have been looked after, after a while they start to go," Ayson said.

Derek Flynn/Fairfax NZ The RNZAF P-3K2 Orion aircraft may be the first to be replaced, pointing to a massive investment by the government.

The need to replace the Hercules and Orions would come as a surprise to no-one, he said.

Numbers released by the New Zealand Defence Force under the Official Information Act showed the number of emergency alerts at Whenuapai Airbase for military aircraft have steadily increased over the last 5 years.

In 2013, there were 12 local standbys or full emergencies at the air force base in Hobsonville. In 2017, that number had risen to 17.

"For more than 20 years, political leaders have known these aircraft would need replacing," Ayson said.

"A range of governments have not addressed this issue as directly as they might, and it just so happens that it now this current coalition government that has inherited this challenge."

Dr Peter Greener, the former academic dean the New Zealand Defence Force's Command and Staff College, said future investment depended on government prioritisation of the varied security interests facing the country.

Both aircraft had their different uses, with the Hercules suited to carrying personal and materials while the Orion was better suited to surveillance, Greener said.

Planning for replacement has been ongoing and the Government was now facing a significant investment to replace both sets of aircraft, he said.

Defence Minister Ron Mark said a Strategic Defence Policy statement, to be released this week, would lay out the Government's military priorities.

"From there we will reassess the Defence Capability Plan to ensure that what we are looking at buying in the future aligns with the vision of this Government," he said.

Among the emergency call outs in 2017, an Orion was forced to make an emergency landing at Whenuapai air base after one of its four engines shut down in October.

In June 2017, a Hercules was left circling the base due to landing issues.

Local standby was an alert when an aircraft approaching the airfield was known to have or suspect to have a problem that would not normally affect a safe landing.

A full emergency standby was a state of alert when an aircraft approaching was known to have or suspected of having a problem that could result in an aircraft accident.