(Bloomberg) — American Airlines Group Inc. said that a tech issue with DXC Technology Co., a third-party vendor that maintains the company’s flight-operating systems, caused a brief groundstop on all US flights on Christmas Eve.

The carrier said Tuesday that a network hardware-related issue has been resolved and flights have resumed. American’s flight-operating system allows for air transport to be coordinated and dispatched, it said. The halt lasted for about an hour. 

“We sincerely apologize to our customers for the inconvenience this morning,” American said in a statement. “It’s all hands on deck as our team is working diligently to get customers where they need to go as quickly as possible.”

The airline didn’t say if it expected any further delays or other knock-on effects.

American Airlines had 3,320 domestic flights and 581 international flights scheduled for the day, according to aviation data provider Cirium. Only 19 of its flights were canceled by the early afternoon, in line with the typical 1% cancellation rate across airlines, Cirium said. 

But there were delays: Only about 37% of American Airlines flights were leaving on time as of the early afternoon, Cirium said, noting that most airlines aim for 80% of flights departing and arriving within 15 minutes of the scheduled time.

The data provider said that most of the delays at American were under two hours. For example, 72% of flights departing out of American’s Dallas hub left within an hour of the scheduled time.

“Based on previous such incidents, it appears American has been able to maintain its schedule, albeit with delays,” said Cirium spokesperson Mike Arnot. “There may be an uptick in cancellations later in the day as crews time out.”

American Airlines shares rose 0.6% at 2:03 p.m. in New York, erasing an earlier decline. DXC Technology stock fell 2.1%. 

American Airlines had said earlier it was experiencing technical issues affecting all of its flights, disrupting operations on a day when the Federal Aviation Administration expects to see about 30,000 US flights across all carriers.

Some online postings said the airline suffered a software outage preventing it from calculating weight and balance requirements for its flights.

The incident comes after Delta Air Lines Inc. suffered a multi-day grounding in July affecting thousands of travelers due to a software glitch. Two years ago, Southwest Airlines Co. suffered a year-end meltdown involving computer-system issues.

–With assistance from Jason Kao and Sana Pashankar.

(Updates with data from Cirium on delays starting in the fourth paragraph.)

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