However, the Federal Aviation Administration (FAA) still investigates the cause of a computer outage, according to the news agency Reuters.
Delta Air Lines, United Airlines, American Airlines Group Inc and Southwest Airlines Co all reported normal operations on Thursday.
A nationwide ground stop was imposed by the Federal Aviation Administration (FAA) over a computer issue that forced a 90-minute halt to all US departing flights.
According to FlightAware, almost 9,600 flights have been delayed so far and over 1,300 canceled. Many industry officials compared the grounding to what occurred after the terror attacks on September 11, 2001.
FAA officials said that a preliminary review traced the problem to a damaged database file, but added there was no evidence of a cyberattack and the investigation was continuing.
The same file corrupted both the main system and its backup, said people familiar with the review, who asked not to be identified.
Transportation Secretary Pete Buttigieg told CNN the ground stop was the "right call" to make sure messages were getting sent correctly and there was no direct evidence of cyberattack. The White House said President Joe Biden still had confidence in Buttigieg.
The outage occurred at a typically slow time after the holiday travel season, but demand remains strong as travel continues to recover to near pre-pandemic levels. It could impact traffic through Friday, said Captain Chris Torres, vice president of the Allied Pilots Association.
The FAA suffered another significant computer issue on January 2 that led to significant delays in Florida flights. Package delivery companies FedEx, United Parcel Service and DHL, which rely heavily on planes, said they faced minimal disruptions on Wednesday.
Separately on Wednesday afternoon, air traffic control manager NAV Canada reported an outage of about 90 minutes in a similar messaging system used in Canada, but said the issue had not caused any flight delays. The agency said it did not believe its outage was related to the FAA one, but was investigating.
(With Reuters inputs)
