Transportation Secretary Sean Duffy says Friday's nationwide ground stop began with an upgrade at a remote FAA location. According to Duffy, contractor L3Harris, a long-time FAA provider, was switching an old, discontinued copper wire over to fiber when the router being replaced started flooding other routers in the air traffic control system. He says that overload caused problems with communications with airplanes and with radar feeds used to guide aircraft. Investigators are still trying to determine whether the cause was contractor or installer error or a faulty piece of equipment. L3Harris says it is supporting the FAA's investigation.

Duffy used the moment to press Congress, saying the country's air traffic control system is incredibly old and needs a full rebuild rather than patchwork repairs. He has called for $50 billion in emergency funding, while critics, including Democrats, have faulted the administration's response to the outage. The ground stop was the longest nationwide grounding in more than two decades, and it left thousands of flights canceled. Whether the failure came down to old equipment, a contractor mistake or both is still unanswered, and the answer is likely to shape the funding debate.