US Airways' flight-operation database malfunctioned because of an "internal technology problem," spokeswoman Amy Kudwa told the Associated Press. A similar problem affected American Airlines' flight-plan system, grounding about 150 flights, spokesman John Hotard said.
Both airlines use a computer system created by Plano, Texas-based Electronic Data Systems. An EDS representative said an "extensive internal evaluation" was under way to determine what happened.
"Right now, we can confirm that there was a system issue," EDS spokesman Jeff Baum said. "It was taken offline for about three hours to remediate."
American Airlines had its planes back up after two hours, while US Airways flights were grounded for about three hours.
The technical problem forced US Airways to delay about 100 flights. American Airlines planned to run its full daily schedule of 2,400 flights, but delays were expected.