The Federal Aviation Administration (FAA) lifted the restriction on Friday, with Transportation Secretary Sean Duffy announcing that US airspace officially reopened at 8.15pm Eastern Time (0115 GMT on Saturday).
However, Duffy warned that flight operations would resume gradually, noting that airlines would need time to restore normal schedules.
“It’s going to be slow,” he told reporters at the White House.
According to flight-tracking platform FlightRadar24, more than 6,600 flights had been cancelled and 8,600 delayed, while another 1,500 flights had already been cancelled for Sunday.
Aviation analysts warned that the four-hour nationwide grounding could continue to affect airline operations for several days.
Duffy said tens of thousands of passengers had been stranded at airports nationwide following the disruption.
He also disclosed that he and Homeland Security Secretary Markwayne Mullin had met President Donald Trump at the White House to discuss the incident.
What caused the disruption?
Duffy said the disruption began at 3.36pm when air traffic control centres experienced instability in their radar and communications systems.
According to him, switches and routers became overloaded with data, resulting in inconsistencies in information transmitted across the network and forcing authorities to shut down the affected system.
“Our switches, our routers actually got overloaded with data and they started to give us inconsistencies in the data from those routers and because of that we shut the system down,” he said.
He maintained that the country never completely lost its radar or communications capabilities, adding that thousands of aircraft were landed safely during the incident.
Although the immediate technical problem had been resolved and flying was considered safe, Duffy stressed the need for a comprehensive upgrade of the country’s ageing air traffic control infrastructure.
Duffy seeks $50bn for aviation infrastructure overhaul
The Transportation Secretary blamed inadequate congressional funding for delays in modernising the US air traffic control system, calling for $50bn to overhaul the infrastructure.
Earlier on Friday, before the disruption, the White House and the Department of Transportation had urged Congress to approve $30.1bn for upgrades to the country’s ageing airports and air traffic control facilities.
“What we have is an incredibly old air traffic control system,” Duffy said.
“Give us the money to fix it.”
Meanwhile, Mullin said there was no evidence so far that the incident had resulted from a cyberattack or a rogue artificial intelligence system, although investigators had not ruled out either possibility.
“It appears this was mechanically driven, however, we’re still looking,” he said.
He added that the National Security Agency was working with the Department of Homeland Security on the investigation.
Two airline officials said the disruption appeared to have affected a telecommunications network operated by L3Harris Technologies, which handles critical radio frequencies used by air traffic controllers to communicate with pilots.
The company had yet to respond to a request for comment.
Passengers face prolonged travel disruption
Despite the reopening of US airspace, passengers continued to face uncertainty as cancellations and delays mounted at airports across the country.
From Boston to Seattle and New York to Los Angeles, travellers crowded departure halls and airline service desks as aircraft remained grounded at airport gates.
Among those affected was 50-year-old Edward Kargbo, from West Chester, Pennsylvania, who was scheduled to travel on a 9pm Ethiopian Airlines flight to Lomé, Togo.
Following the disruption, he said he would have to spend the night at the airport before boarding a rescheduled flight at 6am on Saturday.
“I have to squat the night here,” he said. “I’m stranded.”
Also affected was 47-year-old Louise Maher, whose British Airways flight from Newark to London was caught up in the disruption.
“I might cry at some point but not yet,” she said.
US airlines will not be required to compensate affected passengers because the disruption resulted from an FAA system failure rather than circumstances within the carriers’ control.
The latest incident is only the second nationwide ground stop in the United States since the 11 September 2001 terrorist attacks.
The previous occurrence was in January 2023, when the FAA suspended domestic departures for about 90 minutes following an outage involving its Notice to Air Missions system.
The disruption also weighed on airline stocks, with shares of American Airlines, United Airlines and Delta Air Lines falling between one and two per cent in after-hours trading, while JetBlue Airways dropped by about three per cent.
American Airlines said it was prioritising flights to smaller cities outside its major hubs, as well as international destinations, to reposition aircraft and crews and accelerate the recovery of its operations.
