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The US aviation system was shut down nationwide on Friday after a communications failure at air traffic control centers, grounding all departing flights in only the second such shutdown since September, the Korea Times reports. The nearly five-hour shutdown disrupted more than 20,000 flights, and the FAA lifted the ground stop later that day, though officials predicted air travel would not return to normal until late Sunday. The Chosun Ilbo reports that US Transportation Secretary Sean Duffy said the outage began while L3Harris, a US defense and aerospace company, was replacing control communication lines, and that investigators are looking into worker error and possible equipment defects. The Korea Times adds that the fault may have been a single router installed by L3Harris.