What happens when upgrades to key pieces of infrastructure are put on the back burner

The problems with Defence Force plans and Interislander ferries show the risk of deferred maintenance and upgrades

A Defence Force plane stranding a delegation, the Aratere run aground and a downed pylon causing widespread power outages across Northland are all part of a theme: key pieces of New Zealand infrastructure are constantly breaking down.

Today's episode of The Detail takes a closer look at what led to these issues and what's being done to fix them.

The latest problem hit an Air Force Boeing 757 in Papua New Guinea, which was being used by the Prime Minister and a business delegation for a trip to Japan.

"It seemed pretty familiar," says Newsroom's political editor Laura Walters.

"The Prime Minister, his travelling staff and his foreign affairs officials hop on the plane, everything starts out fine and then they get to Port Moresby and it turns out that there is a fault."

This follows several problems with the 757s - for instance in March one was not able to take off from Wellington while a delegation was on its way to Melbourne. Walters was supposed to be on that flight.

She says there's a huge weigh-up between paying for maintenance and forking out for new planes.

"While we don't want to spend money buying new planes, it seems there is a huge cost that goes into this maintenance and fixing these faults," she says.

"We're looking at tens of millions if not hundreds of millions of dollars across the span of a couple of years - and that's ballooning. It's becoming more and more expensive to keep it in the air."

She compares it to keeping an old car on the road.

"We've all owned one of those crappy old cars and we love them dearly but at some point, it costs more to keep them going than it almost does to just go and buy a new car. Of course, you have to have the capital to put up to buy the new car."

But will the government put up the capital to buy a new plane? Walters is confident the answer is yes.

"The question is less 'are we going to get them' and more 'when are we going to get them'," she says.

Ministers are waiting on a defence capability review, looking at the Defence Force's stock and what can be replaced or upgraded.

"Once that capability plan is delivered, then we'll be able to see a little bit more around what is being recommended, but our understanding is that there will be a recommendation to update these planes or to replace these planes," Walters says…

Go to this episode on rnz.co.nz for more details