NPR reports that the FAA blames Friday's nationwide ground stop — which grounded thousands of flights for about four hours, delayed nearly 25,000 and cancelled over 9,000, leaving tens of thousands of passengers stranded Saturday — on an error while contractor L3Harris upgraded an old FAA telecom line from copper to fiber. Transportation Secretary Sean Duffy says the FAA is investigating whether the error was L3Harris's or a faulty 2001-era router, while FAA administrator Bryan Bedford says there was no evidence of anything nefarious or AI-related and expects full schedule integrity by Sunday.