American Airlines Chief Executive Thomas Horton said on Thursday the company "has a high degree of confidence" that Tuesday's computer network outage that led the carrier to cancel nearly 1,000 flights will not recur.

Horton said American, a unit of AMR Corp, understands the cause of the outage, has ruled out external threats and continues to investigate the issue.

The outage "was unrelated to the merger" planned with US Airways Group Inc, Horton said in an interview.

"It was a unique event and we do not expect that to recur," he added.

The $11 billion merger with US Airways is expected to close in the third quarter, pending approvals, and would cap a wave of consolidation that has helped put U.S. airlines on more solid financial footing. The new American Airlines would be the world's largest carrier.

American Airlines canceled 978 flights on Tuesday because of the computer problem that affected its primary and backup systems. The incident led to 1,500 travelers staying overnight at terminals in Dallas Fort Worth International Airport, American's biggest hub, and prompted Horton to make a video apology to customers.

Though operations were returning to normal, American said it had canceled more than 440 flights on Thursday because of adverse weather. The carrier operates more than 3,500 daily flights worldwide.

Tuesday's incident raised concern about the possibility of future outages, particularly as American prepares to meld operations with US Air. If the merger proceeds, the new company will need to integrate various systems and networks.

Horton, who will be nonexecutive chairman of the new American, said transition teams were working to make sure the merger is carried out with few hitches.

"That really starts with running a good operation, it starts with technology integration going smoothly so we're very focused on those things," Horton said. "They're not easy but we have great teams working on them."

Horton, who took over AMR's top job when American filed for Chapter 11 protection in late 2011, said restructuring savings helped his company on Thursday post its first profitable first quarter, excluding special items and costs, since 2007.

He said the carrier has seen some soft demand this month but added May and June bookings look slightly better than last year.

(Reporting by Karen Jacobs in Atlanta; Editing by Gerald E. McCormick and Mohammad Zargham)