Half Air Force's Hercules aircraft grounded due to repairs

Newshub can reveal the Air Force's Hercules transport aircraft are so hobbled by age that at any one time more than half the fleet is grounded.

They're the workhorses of the New Zealand Air Force, but the problem is they've been working for more than half a century.

There are five Hercules in the fleet, but because they constantly need repairs more than half are grounded at any time.

Maintenance is such a challenge it takes up to three times longer than planned, and on average just two of the five aircraft are available. That means aircraft unable to deliver supplies or help in emergencies.

Phased servicing, which the aircraft needs every 400 flying hours, should take 23 days but instead is taking 50 days.

Group servicing which is needed every 50 months is expected to take 103 days - it's blowing out to 274 days.

On Friday, Defence Minister Ron Mark is making a major announcement about defence strategy.

But don't expect any action on the geriatric Hercules fleet - that wasn't planned until November but Mr Mark is so concerned he's promising to move sooner.