Air traffic operations were gradually returning to normal, the Federal Aviation Administration said, after a systems failure grounded thousands of flights on Wednesday morning.
Thousands of flights were once again able to depart major US airports on Wednesday morning, after the Federal Aviation Adminstration (FAA) lifted a nationwide halt on all domestic flights following a failure of its communications system earlier in the day.
At around 9 a.m. Eastern Time (1400 UTC/GMT), the FAA said that the ground stop it ordered earlier Wednesday was lifted.
The agency ordered all domestic flights to be paused in the early hours of the morning as it worked to restore a system called NOTAM, or Notice to Air Missions system, which issues safety notices to pilots.
The communications system is critical because it alerts pilots to hazards in the air or on the ground, from accumulation of snow on the runway to visibility issues to birds near the airport.
"Normal air traffic operations are resuming gradually across the US following an overnight outage to the Notice to Air Missions system that provides safety info to flight crews," the FAA wrote. "We continue to look into the cause of the initial problem," the agency said.
The White House Press Secretary Karine Jean-Pierre said there was no evidence of a cyberattack at present, but President Joe Biden "directed DOT [US Department of Transportation] to conduct a full investigation into the causes."
Around 8:30 a.m. Eastern Time, the FAA said it cleared flights to depart at Newark Liberty Airport, which serves the New York City area, and the Hartsfield-Jackson Airport in Atlanta. The agency then said it was hoping flights to resume at other airports soon too.
More than 4,000 flights had been delayed by the time, according to FlightAware, a flight tracking website. Another 640 flights had been canceled.
A spokesperson at Germany's Frankfurt Airport told DW at the time of disruption that flights departing to the US were not affected at the airport. But, media reports said several flights from Spain's Madrid international airport to the US were delayed.
A little after issuing its first alert to notify users about the outage around 7:30 Eastern Time (1200 GMT), the FAA sent out a second alert saying some "functions are beginning to come back on line."
The agency said in a third update that it had ordered airlines to pause all domestic departures until 9 a.m. Eastern Standard Time (1400 GMT) to allow it to validate the "integrity of flight and safety information."
As of 6:30 a.m. Eastern Standard Time (1130 GMT), around 760 delays were reported, according to FlightAware website. The flight tracking website reported at the time that massive delays were across flights flying into, and traveling out of, the US. Domestic flights were affected too.
American Airlines then confirmed that the outage was affecting all flights, including all carriers.
"We are performing final validation checks and reloading the system now,'' the FAA said at the time. The aviation agency noted they would update people as soon as more information became available.