Thousands of American Airlines flights scheduled to take place over the Christmas holiday period are without pilots, following a glitch in the airline’s pilot scheduling system that meant all pilots who applied for leave during the holiday period had their requests approved.

Some 15,000 flights out of major hubs, including Miami, Dallas-Fort Worth, Chicago O’Hare and New York’s LaGuardia Airport, are now estimated to be without pilots, CNBC reports.

“The airline is a 24/7 op,” said pilot’s union spokesman, Dennis Tajer. “The system went from responsibly scheduling everybody to becoming Santa Claus to everyone. The computer said, ‘Hey ya’ll. You want the days off? You got it.’”

It is unclear which specific routes have been affected and whether the issue extends to the airline’s services to Asia-Pacific. American Airlines currently flies to Beijing, Shanghai, Hong Kong, Seoul and Tokyo from Dallas-Forth Worth, and to Beijing, Shanghai and Tokyo from Chicago O’Hare Airport.

That said, spokesperson for the airline Matt Miller has said that the airline expects to avoid any cancellations over the holiday period.

“We have reserve pilots to help cover flying in December, and we are paying pilots who pick up certain open trips 150 percent of their hourly rate – as much as we are allowed to pay them per the contract,” he said. “We will work with the APA [Allied Pilots Association] to take care of our pilots and ensure we get our customers to where they need to go over the holidays.”

The scheduling mishap is reminiscent of budget airline Ryanair’s cancellation fiasco earlier this year, which saw the airline cancel flights after it bungled up the allocation of annual leave to its pilots in September and October.