Air New Zealand has grounded a fleet of 18 aircraft after hairline cracks were found on a plane's tail area during a routine maintenance inspection.

Engineers inspecting the Beech 1900Ds, which were operated by subsidiary Eagle Air, have already examined four aircraft and found three were affected.

Eagle Air general manager Carrie Hurihanganui said Eagle Air services were cancelled this afternoon as a precautionary measure and alternative arrangements would be made for the about 800 customers affected.

"We apologise to customers for the inevitable inconvenience caused by undertaking a full check of our fleet. However, the safety of our customers, our staff and our aircraft is paramount and non-negotiable for the airline," she said.

Customers were advised to check flight arrivals and departures for the most up to date schedules.

The Beech 1900D aircraft have been in service with Eagle Air since October 2001 and have an average age of 10.5 years.

The 19-seat aircraft operate to 20 destinations around New Zealand.

- Fairfax NZ News/stuff.co.nz