An hours-long nationwide ground stop issued by the Federal Aviation Administration (FAA) on Friday afternoon was lifted after 8 p.m. ET, Transportation Secretary Sean Duffy said during a White House news conference.

"We’ve opened up the airspace," Duffy said in the White House briefing room, adding it would take time to get flights out. "It's going to be slow," he said. "Check with your airline."

Duffy said the U.S. began to experience "instability for our radar and communications" system at 3:36 p.m., and the ground stop was issued out of an abundance of caution.

"We had intermittent communication and intermittent radar … which is why we shut…

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