Update at 2:06 p.m., Nov. 30, 2017: American Airlines said in a Thursday statement that it has filled most of the flights that a scheduling error left without an assigned pilot or pilots.

The carrier said "only a few hundred" flights remain without assigned pilots and so far it has not had to cancel any flights due to the issue.

"That number of open flights continues to decrease thanks to our pilots who are stepping up to the plate and picking up trips to ensure customers are taken care of," the company said in a statement. "In addition, we have more reserve pilots on hand in December than normal months and they provide us with the ability to fly many of the trips that are currently uncovered."

That figure was contested by the pilots' union, which said "thousands of flights are still listed as unassigned."

"The Allied Pilots Association is able to view in real time December flight crew assignments for American Airlines. That data does not support management's statement regarding December flights that 'only a few hundred are currently unassigned to pilots,'" the union said in a statement. "We remain seriously concerned about the potential for significant schedule disruption for our passengers, pilots, and fellow employees during the critical holiday travel season."

American Airlines spokesman Matt Miller said the carrier's figure differs from the union's because it accounts for the planned use of reserve pilots, which can't be assigned to a trip until the day before.

Original story:

American Airlines is rushing to ensure that thousands of December flights aren’t affected by a scheduling error that left the nation’s largest carrier without enough pilots assigned to work during the busy holiday season.

As many as 15,000 flights between Dec. 17 and the end of the year could be affected by the issue, according to the Allied Pilots Association, the union representing more than 15,000 American pilots. American did not confirm the number put forward by the union or issue its own estimate on the number of affected flights.

“We are working diligently to address the issue and expect to avoid cancellations this holiday season,” the Fort Worth-based company said in a statement. “We will work with the APA to take care of our pilots and ensure we get our customers to where they need to go over the holidays.”

American said it has reserve pilots to help cover the affected flights and the company is offering to pay pilots 150 percent of their hourly rate to pick up certain open trips.

The issue arose from a glitch in American’s scheduling system that allowed pilots to take time off by dropping assigned flights, even when there wasn’t another crew member available to cover for them. Typically, those requests would be denied if adequate staffing isn’t available.

The airline didn’t specify the cause of the glitch, but described it as an isolated incident.

“This is a potential crisis that we see well in advance,” Capt. Dennis Tajer, a spokesman for the union, told The Associated Press. “This is very unusual.”

The pilots’ union has filed a grievance over American’s proposed solution, the news agency reported, alleging that it violates the employees’ labor contract by not including union input and improperly restricting premium pay.

The issue affects flights at about a dozen airports, including DFW International Airport as well as airports in Boston, Miami, Charlotte, Philadelphia, New York and Salt Lake City. The carrier operates about 6,700 flights per day.

The news caught travelers’ attention on social media Wednesday afternoon, prompting concerns about how their holiday plans would be affected.

“Everyone’s already freaking out,” said Brett Snyder, author of the airline industry blog Cranky Flier and president of air travel assistance company Cranky Concierge. “There are a lot of things to worry about and stress you out over the holidays. I wouldn’t let this be one of them.”

Snyder said American will be motivated to prevent the scheduling issues from disrupting any flights, especially after stating publicly Wednesday that it expects to avoid cancellations.

“This kind of thing can happen. They caught it and they’ve stopped it. Now they just have to fill in the blanks" in the schedule, he said. “We’ll be watching closely, but at this point I’m just not that concerned.”