The ground stop was imposed at 3:54pm Eastern Time and remained in place for more than four hours. More than 4,700 flights were cancelled and 10,000 delayed on Friday, while another 700 cancellations had already been recorded for Saturday, according to flight-tracking service FlightRadar24.

The disruption also affected international travel, forcing airlines to cancel flights departing from Canada and Europe. Aviation analysts warned that it could take several days for airlines to restore their normal schedules.

The Department of Homeland Security said there was no immediate evidence that the outage had been caused by a cyberattack, although authorities were investigating its possible causes.

“There is no indication as of yet that this was a nefarious attack against us. It's just a telecommunications outage as of right now,” Homeland Security Secretary Markwayne Mullin told reporters outside the White House.

He sought to reassure the public, saying there was no reason to fear for the safety of passengers and describing the incident as different from the September 11 attacks.

Mullin said investigators were examining all possible causes, including a new artificial intelligence-powered air traffic control system.

Telecommunications failure disrupts air traffic

The FAA said the nationwide ground stop followed a communications failure affecting air traffic control centres. Technicians were working to identify and resolve the problem.

The agency described the suspension of departures as a precautionary measure to maintain aviation safety after a temporary telecommunications outage affected its operations.

Departures were halted at airports across the country, while incoming international flights were handled individually. Aircraft already in the air were allowed to continue to their destinations and land safely.

Some arriving aircraft were left waiting on taxiways as airport gates filled up, adding to congestion and delays.

The incident has renewed concerns about the reliability of US air traffic control infrastructure, which has faced repeated equipment failures, communication problems and shortages of air traffic controllers.

Thousands of flights cancelled or delayed

The disruption stranded passengers at airports across the country, with major airlines including United Airlines and American Airlines warning of widespread cancellations and delays.

Some passengers were left waiting aboard aircraft, while others were returned to departure gates as airport operations were disrupted.

The shutdown affected airports from Boston to Seattle and New York to Los Angeles. The FAA said all flights already in the air had been accounted for and were allowed to land.

The incident was only the second nationwide ground stop since the September 11, 2001 attacks.

The previous nationwide suspension occurred in January 2023, when the FAA halted domestic departures following a computer failure affecting its Notice to Air Missions (NOTAM) system. That disruption lasted about 90 minutes.

Outage renews scrutiny of ageing aviation infrastructure

Friday’s communications failure has intensified calls to modernise the US air traffic control system, much of which relies on decades-old technology.

The incident came as the White House and the Transportation Department urged Congress to approve an additional $30.1 billion to upgrade the country's airports and air traffic control infrastructure.

In a letter to lawmakers, Transportation Secretary Sean Duffy and Office of Management and Budget Director Russell Vought described the investment as essential to modernising the national airspace.

They said the funding would help provide a more reliable telecommunications network for air traffic controllers, modern hardware and software, updated control towers and improved airport infrastructure.

Congress had already approved $12.5 billion over five years in July 2025 to upgrade air traffic control facilities and increase the recruitment of controllers. The latest request seeks additional funding for a wider overhaul.

On November 5, the FAA also announced plans to replace outdated floppy-disk-based systems used to manage weather and other critical information at more than 400 air traffic control facilities by the end of 2028.

The project will replace four systems dating back to the 1980s with a single digital platform.

The FAA has experienced similar communications failures in recent years, although previous incidents generally affected individual airports or regions rather than the entire national aviation network.

In September, thousands of flights in the northeastern US were delayed or cancelled after a circuit failure at a Philadelphia air traffic facility and the accidental severing of a fibre-optic cable in New Jersey disrupted operations.

Authorities have yet to establish the precise cause of Friday’s nationwide outage.