Sean Duffy, the transportation secretary, said the airspace was now open and the problem had been identified

The Federal Aviation Administration (FAA) has lifted a nationwide ground stop that was declared Friday afternoon, delaying or canceling more than 11,000 US flights, according to aviation tracker FlightAware, and throwing airports into sudden chaos.

The FAA confirmed the airspace was open in an advisory on its website. “So at 8.15 tonight, Eastern Time, we’ve opened up the airspace,” Sean Duffy, the US transportation secretary, said. “But it’s going to take us some time to unwind what’s happened this afternoon.”