Computer issues that on Wednesday grounded all United Airlines (UAL) flights have been resolved, with a ground stop lifted, federal aviation authorities said.
"We experienced a network connectivity issue this morning," United said by email. "We are working to resolve this and apologize to our customers for any inconvenience."
It is the second time in as many months that United flights were delayed because of computer glitch. About a month ago, the carrier held flights for about 40 minutes when their dispatch system went off line.
Flights already aloft remained in operation, according to Flightradar24, a website that tracks airplanes.
United's stock declined 1.3 percent, or 73 cents, to $53.58 in early trading.
Word that United flights had ceased first spread on Twitter, with many passengers reporting they had been delayed.