According to Isar News, The unprecedented shutdown, only the second nationwide grounding of US flights since the September 11, 2001, attacks, was triggered by problems with an aging air traffic control system that became overloaded following technology upgrades, US Transportation Secretary Sean Duffy said.

The disruption began at 3:36 p.m. ET, when the FAA experienced telecommunications problems, including intermittent radar outages at regional control centers responsible for managing high-altitude flights and communication failures with some aircraft.

The agency issued a nationwide ground stop at 3:53 p.m. ET, when more than 3,500 aircraft were already in the air heading toward US airports.

As the shutdown continued, aircraft gradually landed or were diverted, reducing the number of planes in the air to approximately 400.

The FAA lifted the ground stop at 8:15 p.m. ET, allowing flights to resume, although Duffy warned that restoring normal operations would take time.

By then, approximately 6,700 flights had been cancelled and another 8,600 delayed, according to flight-tracking website FlightAware.

The disruption also affected Canadian passengers and airlines because flights operating between Canada and other destinations often pass through US airspace.

Airlines faced the additional challenge of repositioning diverted aircraft, managing staffing complications and accommodating passengers stranded at airports, with operations expected to take several days to return to normal.

Passengers affected by cancellations and delays were advised to contact their airlines for updated schedules and rebooking arrangements.

Addressing the cause of the failure at a White House briefing at 8:30 p.m. ET, Duffy blamed outdated infrastructure that had become overwhelmed following recent upgrades.

"What we have is an incredibly old air traffic control system," he said, describing instability in communications with aircraft and radar data across the FAA's 22 regional air traffic control centers responsible for higher-altitude flights.

"It's an old system that went down and went down everywhere. It got overloaded," Duffy said.

He warned that the existing infrastructure remained vulnerable to further disruptions, saying, "It's going to continue to fail."

Duffy also said there was no evidence indicating a cyberattack had caused the outage, although investigators had not ruled out that possibility.

Turning to the broader problem of aging aviation infrastructure, the transportation secretary urged Congress to approve funding for a complete overhaul of the country's air traffic control network.

Friday's shutdown was the third major nationwide disruption to US air traffic operations in the past quarter-century.

Following the September 11, 2001, terrorist attacks, the FAA closed US airspace for two days, while a separate communications failure on January 11, 2023, halted domestic departures for approximately 90 minutes.