CHICAGO (REUTERS) - American Airlines said its operations returned to normal on Wednesday after it cancelled nearly 1,000 flights on Tuesday because of a computer outage.

The airline also said it halted 81 flights on Wednesday to reposition crews and planes after the outage. The carrier had a total of more than 300 flight cancellations for the day, most of them tied to bad weather in the Chicago area.

At Dallas Fort Worth International Airport (DFW), American's biggest hub, the carrier cancelled 37 fights for Wednesday but was operating on schedule, spokesman David Magana said.

"We had about 1,500 passengers who opted to stay overnight inside DFW Airport terminals, but today the passenger check-in lines have subsided," he added.

On Tuesday, American grounded its US flights for several hours because of intermittent computer outages. The carrier canceled 978 flights, and hundreds more were delayed. American said a software issue that affected its primary and backup network systems caused the problem, and declined to provide more details.

The carrier said on Wednesday it added extra flights to help customers whose travel plans were disrupted by the outage. The extra service included flights between Chicago's O'Hare airport and DFW, Los Angeles and DFW, and Los Angeles and Miami.

American, a unit of AMR Corp, which plans to merge with US Airways Group this year, said it had no evidence that the issues were related to bombings in Boston on Monday. The carrier operates more than 3,500 daily flights worldwide.

Bill Curtis, chief scientist at CAST, a software quality analysis firm, raised the possibility that American could face more disruptions at it merges with US Airways. The combination would create the world's largest air carrier.

Should the merger be approved, the bigger company will face the task of integrating intricate systems, including reservation and baggage handling, computer networks and terminals, a process that has complicated other mergers.

United Continental made a number of changes following its 2010 merger. As it shifted to a single reservations system and implemented other processes, on-time arrivals suffered.

Last year, computer outages at United in the wake of some of those changes stranded passengers at airports around the country.

"Modern airlines run off a lot of information systems that have to interact with each other," Mr Curtis said. "Can we make them foolproof? No."

He said the Tuesday outage at American could have resulted from a number of problems such as software that was incorrectly designed. He added the incident was not likely to be the last such outage, especially as companies merge. The American-US Airways merger is expected to close in the third quarter.

"American is going to have some struggles to merge these two airlines, the systems at US Air and American," Mr Curtis said.

American Airlines did not immediately provide a comment on Mr Curtis's remarks.

Robert Mann, a former American employee who is now an aviation consultant, said he did not see any "exceptional risk"of such outages as American and US Air merge. He likened the Tuesday outage to a snowstorm that requires a day or two to restore normal operations.

He said transitioning to new systems was a task most airlines that merge understand is necessary, with some doing it well and others having problems.

"Good planning, good execution gets you through that," Mr Mann said.