Most people booked to fly on Air New Zealand's ATR fleet tomorrow (Tue) will be able to travel, the airline says.

The airline's 11-strong ATR72-500 fleet, operated by Mount Cook Airlines, was grounded for safety inspections yesterday after hairline cracks were found around the cockpit windows of one aircraft.

About 60 one-way services were cancelled yesterday, affecting about 3000 customers, with a further 2000 customers affected by cancellations today.

One of the 68-seat aircraft was back in service yesterday and a second returned to the skies today.


Three more ATRs would be brought back into service tomorrow, with two more joining them on Thursday.

Three others would not be ready until Sunday and the final aircraft was undergoing planned maintenance, Mount Cook Airline general manager Sarah Williamson said.

Those back in service, combined with extra planes from Air NZ, meant most passengers booked to fly on Mount Cook flights tomorrow would be able to travel, she said.

Mount Cook Airlines transports about 4000 passengers per average day, and expects to be able to fly 97 per cent of booked passengers to their destinations tomorrow.

"As a result of more aircraft re-entering service we will be able to get nearly all of our passengers to their destination, albeit there will be changes to the timing of some flights,'' Ms Williamson said.

"I would like to thank Mount Cook customers for their patience and understanding.''

"We would like to assure them that we are working as quickly and thoroughly as we can to get our aircraft back flying. The safety of our customers, our staff and our aircraft is paramount and non-negotiable for Mount Cook and Air New Zealand.''

Customers booked to fly should visit to check their flight status, or call the contact centre on 0800 737 000. Flight numbers for Mount Cook start with NZ5.