The Trump administration says Friday’s four-hour nationwide Federal Aviation Administration (FAA) ground stop that delayed or canceled thousands of flight stemmed from routine maintenance.

At a news briefing on Saturday, the US transportation secretary, Sean Duffy, said that the issues began when a contractor was performing “routine maintenance” at a remote FAA facility to “switch telecommunications lines” from copper wire to fiber optic cable.

“What we’re working to determine is whether we had incompetence,” Duffy said, “or did they install a faulty router.”

He added: “Once we were able to isolate the work that was being done at this remote location, all of our systems came back online,” and the ground stop was lifted.

However, travel chaos continued across the US on Saturday .

At the briefing, the FAA’s head, Bryan Bedford, apologized to passengers and said he believed that the worst of the disruption “is behind us”.

“We will still have delays and cancellations today, but that will set us up for a…