The United States lifted a nationwide ground stop at its airports on Friday, with officials saying the disruption was not caused by a cyberattack or a wider Microsoft outage, AFP reported. The halt lasted more than four hours.

Transportation Secretary Sean Duffy said US airspace was "opened up" and blamed "old hardware" for the disruption. The Federal Aviation Administration (FAA) said on Friday night that departures could resume. Trump administration officials had described the systems involved as "overloaded" and "outdated," AFP said.

The FAA had grounded all flights nationwide on Friday afternoon, causing hundreds of diversions. It cited "extraordinary circumstances" caused by communications problems at regional air traffic control centres.

Homeland Security Secretary Markwayne Mullin told reporters at the White House that the introduction of some new technology into an old air traffic control system had overwhelmed it. He could not rule out another outage. International flights were being handled case by case, he said, and some were seen taking off on Friday evening.

Duffy also called on Congress to provide $50 billion for an overhaul of the air traffic control systems, which he described as incredibly old, according to a live-updates report by Atlanta television station WSB-TV. Mediaite reported that Duffy made the demand as he announced the ground stop had been lifted, criticising Congress over aviation system upgrades.

AFP said there was no indication that the communications failure was linked to a cyberattack. It said the stoppage was the first nationwide ground stop since January 2023, when a key FAA computer system malfunctioned, and the second since the aftermath of the September 11, 2001, attacks.

Airlines will not be able to return to normal operations immediately because many of their aircraft and crews are out of position, AFP said. WSB-TV's live updates reported that nearly 5,000 flights had been cancelled nationwide.

According to Cirium, an aviation analytics company, at least 827 flights had been diverted as of 7:05 pm EST. Of these, 670 returned to their departure airport, and 157 were redirected to another airport. Washington Dulles, Los Angeles International, Cincinnati/Northern Kentucky, and Nashville were among the airports that received many of the diverted flights.

About 11,000 flights carrying more than 1.5 million passengers were scheduled to depart US airports after 4 pm EST, raising the likelihood of more cancellations and diversions, AFP said.

Jeff Dubner, a Washington attorney, was on an Alaska Airlines flight from Los Angeles that was taxiing for departure when it stopped. "It's frustrating," he told AFP, saying he expected a longer delay than usual.

Source: AFP/WSB-TV/Mediaite