The US stops every departing flight in the country after air traffic control loses its communications

US flights began moving again at 8.15pm Eastern time on Friday (9.15am AWST Saturday), when Transportation Secretary Sean Duffy said the airspace had reopened. Every departure from a US airport had been on the ground since 2.54pm Central time (4.54am AWST), after communications failed across all of the country’s en-route air traffic control centres.

More than 5,000 flights had been cancelled by the time the stop was lifted, and more than 10,000 delayed, on one of the busiest travel afternoons of the week.

The Federal Aviation Administration’s order had said all airports were ground stopped “due to extraordinary circumstances and for reasons of safety”. About 3,000 aircraft were in the air when it was given; they were allowed to land.

What caused it?

Duffy said the stop followed instability in radar and communications at the control centres. “Our switches, our routers, actually got overloaded with data,” he said, and they began giving controllers inconsistent data. He called it “an incredibly old air traffic control system” and used the moment to press for more FAA funding.

Mullin has since given the first account of what tipped it over: new equipment and patches that the FAA had been installing on the older system appeared to overwhelm its routers. He said the outage was a telecommunications problem, not a “nefarious act”, and not connected to this week’s Microsoft outage, though officials are still investigating. The network that links the control centres is run for the FAA by the defence contractor L3Harris, which had not commented.

Earlier, the FAA had described a “temporary telecommunications outage” and said every flight was accounted for. Mullin said there was no cyberattack in what officials had seen so far, but that they were still working through the process and could not rule anything out. The stop came days after the FAA expanded an AI-assisted traffic management system nationwide; the company behind it, Air Space Intelligence, said its system did not cause the stop, and officials have not linked the two.

How big was the disruption?

By 7.30pm Eastern (8.30am AWST), flight tracking data showed 10,079 delays and 4,238 cancellations on flights within, into or out of the US, and cancellations passed 5,000 within the hour. That compares with about 1,000 cancellations the day before and fewer than 100 on Wednesday. Aviation data firm Cirium counted about 11,000 flights scheduled to leave US airports after 4pm Eastern on Friday. Passengers reported aircraft returning to gates, rebookings over and over, and long queues at baggage desks in Chicago and Denver. FedEx activated contingency plans for freight, and the organisations that move donor organs by air said they were monitoring the stop.

What does it mean for Australians?

Flights already in the air to the US were able to land, and some long-haul departures had been let out during the stop: San Francisco cleared Pacific-bound flights from 3pm local time (7am AWST). Qantas said the outage had not affected its flights and urged customers to check its app before going to the airport. Anyone flying to, from or within the US this weekend should still check with their airline before leaving home: domestic connections are where the knock-on delays will land.

Why does this matter beyond one bad afternoon?

The en-route centres handle aircraft at cruising altitude across the whole country, so a failure that hits all of them at once leaves no backup region to take over. On the same day, the FAA and the White House asked Congress for another US$30.1 billion to overhaul the air traffic control system, on top of US$12.5 billion approved last year. Duffy’s account of routers choking on data is likely to become the central exhibit in that argument.

VNN will update this story as more is confirmed.