The aircraft were all ATRs propeller-driven 68-seaters operated by Air New Zealand subsidiary Mt Cook Airlines on regional services. About 60 flights were cancelled after hairline cracks were found in an aircraft during a routine overnight check. Mount Cook general manager Sarah Williamson said they expected to operate approximately two-thirds of their normal seat capacity on Monday as the ATR fleet was checked and returned to service. The inspections were being conducted in conjunction with aircraft manufacturer ATR. "We are making good progress. Of our fleet of 11 aircraft, we expect two aircraft to be operating tomorrow; three others require closer examination and five are well advanced in the inspection process," she said.