What we know about the FAA nationwide ground stop

The Federal Aviation Administration took an extraordinary step Friday afternoon by issuing a nationwide ground stop. No planes are taking off at any airport and millions of passengers are stranded.

The U.S. air travel system is slowly getting back off the ground. The Federal Aviation Administration has lifted the rare nationwide ground stop it issued earlier today, citing telecommunications failure. That grounded thousands of planes at airports across the country, stranding millions of passengers. NPR's transportation correspondent Joel Rose is here. We've been talking all afternoon and evening trying to sort this out. Joel, now we have a little bit of a resolution, but not really. What's the latest?

JOEL ROSE, BYLINE: Yeah. We just heard from the transportation secretary, Sean Duffy, that, as you said, the airspace has reopened. The ground stop is lifted. But it's going to take some time to get this hourslong - to get through the backlog of canceled and delayed flights. And it's going to take even longer to figure out, apparently, what happened here.

During the news conference, Duffy said that investigators are still trying to understand exactly what the problem was. Duffy blamed the - Duffy cited intermittent communications, intermittent radar and blamed this on outdated air traffic control equipment that was overloaded with data. We have old switches, old routers, he said. It's an old system that went down. It got overloaded. Here's more of what Duffy said.

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