American Airlines did not immediately respond to request for comment.
The Allied Pilots Association, a union that represents commercial pilots, said a glitch in the system American Airlines uses to schedule time off for pilots approved all the PTO requests, which means more than 15,000 flights between December 17-31 that are short some crew, Gizmodo reported.
"It's a really weird situation", a union spokesman told CNBC.
A glitch in the system that bids for pilots' time off based on seniority is behind the shortage, the Allied Pilots Association union said.
The shocking news was later substantiated by ABC7 reporter Sam Sweeney.
American was little changed at US$49.25 (RM202.15) at the close in NY, after erasing an earlier gain of as much as 3.9 per cent.
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If you're flying American Airlines this holiday season, you might want to reconsider your travel plans. Still, industry experts say the increased complexity of airline computer systems is to blame for a growing number of glitches that have recently grounded airplanes and posted ultra-cheap airfares.
"The system went from responsibly scheduling everybody to becoming Santa Claus to everyone", said American captain Dennis Tajer, according to CNBC. The Allied Pilots Association reportedly claims that the carrier's solution to its scheduling conflict violates its labor pact, and it has filed a grievance.
Pilots were notified of the error on Friday via email, along with a plea for pilots to give up scheduled vacation time in exchange for 150 percent of their normal hourly range to pick up some of the flights.
Affected by the computer glitch were flights originating in Philadelphia, Dallas-Fort Worth, Boston, Miami, New York, Salt Lake City, and Charlotte, N.C., according to a company memo to the union reported by Bloomberg News on Wednesday.
"We're working diligently to address the issue and expect to avoid cancellations this holiday season", read one reply.