WASHINGTON — The Federal Aviation Administration says air traffic operations are gradually resuming across the U.S. after a critical overnight system outage. The agency had ordered all domestic departures to pause until 9 a.m. Eastern Wednesday morning, causing a nationwide ripple effect of flight delays and cancellations.
"Normal air traffic operations are resuming gradually across the U.S. following an overnight outage to the Notice to Air Missions system that provides safety info to flight crews," the FAA said on Twitter. "The ground stop has been lifted. We continue to look into the cause of the initial problem."
U.S. Transportation Secretary Pete Buttigieg said on Twitter that the NOTAM system, which pilots check before flights to review potential hazards, is "fully restored," and that he has ordered a process to find the cause of the outage and recommend next steps.
The FAA ordered the grounding as it worked to restore the system, which went offline Tuesday night. It said the pause would let it "validate the integrity of flight and safety information."
The NOTAM system is designed to provide pilots and air traffic controllers with critical information before they take off, like runway hazards or adverse weather conditions. Flights in the sky during the outage were safe to land, the agency said.
United States Press Secretary Karine Jean-Pierre said earlier that President Joe Biden has been briefed on the outage.
"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 wrote on Twitter.
Biden addressed the issue himself Wednesday while leaving the White House to accompany his wife to a medical procedure: “I just spoke to Buttigieg. They don’t know what the cause is. But I was on the phone with him ... I told him to report directly to me when they find out."
He said officials expect to know more about what happened in "a couple of hours."
Earlier Wednesday, United Airlines said it was temporarily delaying all domestic flights and waiting to learn more. American Airlines made a similar statement, adding that the outage "is impacting all flights including all carriers."
More than 9,300 flights were delayed within, into or out of the U.S. as of about 6 p.m. Eastern, according to flight tracking website FlightAware. More than 1,300 U.S. flights were canceled.
According to the Associated Press, some medical flights could get clearance during the outage and it was not impacting military operations. However, the groundings impacted almost all aircraft, including shipping and passenger flights. Aviation data firm Cirium said some 21,000 flights were scheduled to take off in the U.S. Wednesday, mostly domestic.
The industry-wide problem comes less than a month after thousands of flights were canceled or delayed after Christmas, when Southwest Airlines faced major delays due to logistical and tech issues during a winter freeze.