A computer malfunction at United Airlines, part of UAL, halted all departures systemwide for two hours Wednesday, the carrier said.
The cause was not immediately clear.
The outage lasted from 8am to 10am CDT, when departures were able to resume, spokeswoman Robin Urbanski said.
"We were experiencing a computer outage and now our computers are back up," she said. "Right now we're working hard to resume our operations."
US Federal Aviation Authority spokesman Allen Kenitzer in Seattle confirmed that all United flights across its system had been grounded because of the computer problem.