Transport Secretary Sean Duffy told a news conference that a nationwide ground stop on Friday resulted from a problem that emerged after a copper wire upgrade, leading to the shutdown of air traffic across the continental United States.

The upgrade involved replacing old copper lines with fiber, carried out by contractor L3Harris, and a router under maintenance began flooding other air‑traffic‑control systems, creating communication failures with aircraft.

No flights were permitted to depart from the continental U.S. for more than four hours, starting at 15:54 EST (19:54 GMT) on Friday, marking the longest ground stop since the September 11, 2001 attacks.

Tracking data from FlightAware showed that more than 3,500 flights were cancelled and over 2,000 delayed on Saturday, with some passengers stranded on the tarmac.

FAA head Bryan Bedford said investigators found no evidence of malicious activity or AI‑related interference, emphasizing that the issue appears technical rather than a cyber‑attack.

Duffy warned that similar incidents could recur unless Congress approves a $30.1 billion funding request from President Donald Trump to modernise air‑traffic‑control infrastructure.

Former TSA administrator John Pistole noted the system’s resilience in restoring operations within four and a half hours but cautioned that future failures remain possible.