American Airlines said on Friday that it believes it has covered all the flights that were potentially affected by a computer glitch and staffing issue that had many worried about the effect on holiday travel.

American Airlines and the pilots’ union Allied Pilots Association (APA) both said a deal had been reached to make sure there will be staffing for all flights.

A glitch in the computer system American Airlines pilots use to schedule time off raised concerns this week that many planes would lack pilots and other essential personnel.

The APA had said that more than 15,000 American Airlines flights scheduled between December 17 and December 31 lacked a captain, co-pilot or both when a problem was discovered in the company’s scheduling system. Pilots were allowed to take vacation days in the last two weeks of December even if there wasn’t another pilot available to operate the flight.

Both sides said Friday that a deal had been reached on premium pay and the APA dropped its grievance.

A letter sent to pilots earlier this week showed the bulk of the holes in the schedule were in late December. American Airlines was seeking captains and first officers for flights originating in cities including Boston, Charlotte, Chicago, Dallas, Miami, New York, Philadelphia, St. Louis and Washington D.C.

The carrier has about 15,000 pilots and roughly 200,000 flights scheduled during December.

American Airlines discovered the software issue the day after Thanksgiving and has been working since Black Friday to fill the unassigned flights. The glitch, which occurred with the system that allows pilots to drop or trade assigned trips, allowed thousands more pilots to be off during the Christmas travel season than it should have. It has since been fixed.

The airline has apologized to pilots for the inconvenience the error has caused.

“This was a terrible screw up by American Airlines,” said Henry Harteveldt, president of Atmosphere Research Group, which tracks the airline industry.

Roughly 30 million people are expected to fly during the busy holiday season.