The US Federal Aviation Administration (FAA) canceled a ground stop on all national flights hours after stopping departures at US airports on Friday.
"We have old switches, old routers, we use 1980s old copper lines. We use an old system," US Secretary of Transportation Sean Duffy said. "It was a legacy network problem."
US Homeland Security Secretary Markwayne Mullin said there was no indication the communications breakdown was the result of a cyberattack.
Over 4,500 flights were canceled Friday and about 700 for Saturday and over 10,000 flights within, into, or out of the United States were delayed, according to the FlightAware aviation tracker. With some 11,000 flights scheduled to depart from US airports after 4 p.m. local time (2200 UTC), more cancellations were expected, according to Cirium, an aviation analytics company.
"All departing traffic should remain groundstopped until further notice," the FAA had said earlier Friday.
The agency said the ground stop was "due to extraordinary circumstances and reasons for safety." The FAA cited a temporary telecommunication outage and said, "Every flight has been accounted for and international flights will be handled on a case by case basis."
The agency said flights were halted "out of abundance of caution."
In a post on X, Duffy said the stop was due to a communication issue impacting all Air Route Traffic…
