Delta(NEW YORK) — Delta operations are being restored Monday morning after a system outage caused delays and about 170 cancellations Sunday night. Some 80 flights scheduled to depart Monday are still canceled, with more canceled flights possible, the airline said.

According to the company’s website, “essential IT systems” went down Sunday evening around 6:30 p.m. and were restored within hours. All airline systems “were back to normal shortly after midnight Monday.”

Delta CEO Ed Bastian apologized for the outage in a statement on the airline’s website.

“I want to apologize to all of our customers who have been impacted by this frustrating situation,” he said. “This type of disruption is not acceptable to the Delta family, which prides itself on reliability and customer service. I also want to thank our employees who are working tirelessly to accommodate our customers.”

Though Delta is offering a fee waiver to all customers with flights scheduled for Jan. 29 and Jan. 30 (for rebooking Feb. 3), the airline advises that customers traveling Monday check their flight status at delta.com and through the Fly Delta mobile app.

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