"We've returned to normal operations," United spokesman Charles Hobart said. Less than 200 flights were affected by the outage, which involved the carrier's dispatch system that enables communication with airplanes prior to departure, he added.

He said Chicago-based United had waived flight-change fees for customers holding a ticket for travel on Thursday, and travellers whose flights were delayed for at least two hours could get refunds.

The latest outage was the third such incident to affect United operations this year. In August, a temporary network outage hampered United's website and airport functions, causing flight delays and cancellations.

United bought Continental in a $3.17 billion stock deal in 2010, creating the world's largest air carrier. The merged company has had problems integrating operations.

In March, United adopted Continental's reservation system, triggering computer glitches that caused flight delays, faulty kiosks and jammed phone lines.

Last month, the carrier said it was looking to win back customers who had turned to competitors after its technology changes had hurt service .

Shares of United Continental fell 2.4 percent to $19.51 on Thursday.

(Reporting by Karen Jacobs and Ben Berkowitz; Editing by Jeffrey Benkoe and Jim Marshall)

• A Permanent Economic Emergency