AMERICAN AIRLINES Group, Inc. is rushing to resolve a scheduling fault that gave time off to too many pilots in December 鈥 a flaw that has left more than 15,000 flights without sufficient crew during the holiday rush, according to a union for the carrier鈥檚 pilots.

The Allied Pilots Association estimated the number of affected flights, from Dec. 17 to Dec. 31, based on information provided by the carrier, said Dennis Tajer, a聽spokesman for the union. American spokesman Matt Miller聽declined to quantify the potential number of flights involved, saying the airline expects to correct the problem in time to prevent service disruptions.

鈥淲e are working diligently to address the issue and expect to avoid cancellations this holiday season,鈥 Miller said. The number of flights involved will decline each day as the carrier reassigns them, he said.

The computer-system problem will force American to rebuild its staffing schedule, similar to what airlines must do after major weather disruptions, said John Cox, chief executive officer of consultant Safety Operating Systems and a former commercial airline pilot. Revenue will take a hit if American has to scrub many flights. At a minimum, the carrier is likely to face higher labor costs just as investors are stepping up scrutiny of airline expenses.

鈥淚t will be a challenge, but I don鈥檛 think there will be mass cancellations,鈥 Cox said. 鈥淭here鈥檚 going to be a lot of midnight oil spent on it, but I think they鈥檒l get the vast majority of them covered one way or another.鈥

American was little changed at $49.25 at the close in New York, after erasing an earlier gain of as much as 3.9%. All other major US airlines advanced significantly, pushing an聽index of the five biggest US carriers to the biggest increase in almost two months. American has climbed 5.5% this year, compared with 2.7% for the index.

The Fort Worth, Texas-based carrier is offering pilots 1.5 times their normal hourly wage to pick up some of the flights, the top rate laid out in their contract, Miller said. It also has a higher-than-normal number of pilots on reserve during December who will fill 鈥渁 good chunk鈥 of the affected flights, he said.聽

The聽APA, representing 15,000 American pilots, has filed a grievance, saying the聽proposed solution violates its labor pact. The union wants to consult with American to find a remedy that will motivate pilots to give up vacation they鈥檝e already been granted after years of working over the holidays, Tajer said.

鈥淭his is certainly not routine,鈥澛燭ajer said. 鈥淭his is a crisis right now, and in that crisis, they鈥檝e gone solo.鈥

The glitch caused the scheduling system to show that American had ample staffing coverage for some planned flights when it actually didn鈥檛, Miller said. The system let pilots drop some trips they had been assigned next month because it wrongly showed there were sufficient crew members willing to pick up the flights.

The carrier has made adjustments and expects the schedule to function smoothly from now on. American, the world鈥檚 largest airline, operates about 6,700 flights a day.

Flights that are scheduled without a captain, first officer or both originate from Dallas-Fort Worth International, American鈥檚 largest hub, and airports in Boston, Miami, New York, Philadelphia, Salt Lake City and Charlotte, North Carolina, according to a company memo to the union, which was seen by Bloomberg News. 鈥 Bloomberg