A computer outage grounded flights across the US on Wednesday morning as the Federal Aviation Administration scrambled to get the system back up.
The FAA's system to convey safety information to pilots and other airline personnel, called the Notice to Air Missions System, had "failed," the agency said, affecting operations across the US.
More than 1,300 flights were delayed on Wednesday morning, according to FlightAware.
The FAA ordered airlines to pause domestic flights until 9 a.m. ET as it worked to restore the system.
By 8:50 a.m., the agency announced that the ground stop had been lifted and traffic operations were "resuming gradually."
It wasn't immediately clear what caused the outage, but White House press secretary Karine Jean-Pierre said in a statement that it did not appear to be a cyberattack.
"There is no evidence of a cyberattack at this point, but the President directed DOT to conduct a full investigation into the causes," Jean-Pierre tweeted.
Secretary of Transportation Pete Buttigieg said that the FAA was "working to resolve this issue swiftly."
On Wednesday evening, the agency said it had traced the outage to "a damaged database file," but that it was continuing to review the root cause.
"We are working diligently to further pinpoint the causes of this issue," the FAA said in a statement, "and take all the needed steps to prevent this kind of disruption from happening again."
Brandon Warren, a 25-year-old master's student at Syracuse University, had been at the Dallas Love Field Airport since 4 a.m. CT. He was traveling back to Syracuse, New York, on Wednesday morning with a transfer in Baltimore, but both flights had been delayed, he told BuzzFeed News.
Warren, who was running on two hours of sleep, said airline staff informed them about the delay about 15 minutes before boarding.
“It was only going to be about 50 people on the plane, so it was fairly empty,” Warren added. “But now we have a packed airport because everyone else's flights got delayed. So it's all backed up now.”
The system outage comes on the heels of a chaotic holiday travel season, during which tens of thousands of passengers were stranded after Southwest Airlines canceled more than 16,700 flights because of technical issues.