Air New Zealand expects almost all of its regional services to be operating on March 20 after the temporary grounding of its fleet of 11 ATR 72-500 turboprops caused major flight disruptions over the past few days.

The aircraft were grounded for unscheduled inspections after hairline cracks were found around the cockpit windows on one ATR 72-500 during routine maintenance. Most of the inspections had been carried out by the evening of March 19.

The carrier’s ATRs, which have an average age of 10.9 years, have been operated by subsidiary Mount Cook Airlines since 1999.

Five of the ATRs will be operational by the end of March 20, and another two will return to service by March 22. Three ATRs have been “confirmed as requiring work” which is likely to be completed by March 25. The remaining aircraft is undergoing planned maintenance.

Mount Cook Airlines says it will be able to handle about 97% of the passengers booked on its flights on March 20, with the help of additional Air New Zealand mainline aircraft. Timing changes will be needed for some flights, however.

The carrier canceled most of its ATR services – or about 60 one-way flights – on March 18 due to the inspections. About 3,000 customers were affected by the cancelations on that day. There were roughly 2,000 customers affected by cancelations on March 19.