A nationwide ground stop that resulted in thousands of flight cancellations across the United States was triggered by technical complications following a copper wire upgrade, Transport Secretary Sean Duffy announced.
During a news conference, Duffy explained that the government is currently investigating whether the failure stemmed from faulty equipment or potential incompetence by the contractor responsible for the work.
The contractor, a technology provider known as L3Harris, had been performing maintenance to transition communications infrastructure from copper wire to fibre. According to Duffy, the system relies on an "incredibly old telecommunications system," noting that the specific wire being replaced was so outdated that it was being discontinued.
The disruption began when a router undergoing maintenance started flooding other air traffic control systems with data. This generated communication failures with aircraft, forcing the government to shut down the nation's airspace to ensure safety.
L3Harris stated on Saturday that it had completed over 70% of the modernization work prior to the shutdown. The company confirmed it is working closely with the Federal Aviation Administration (FAA) to understand the conditions that led to the 13 November incident, emphasizing that it takes the impact on travelers and airlines seriously.
While an investigation is ongoing, the government has stated it does not believe the event was the result of a cyber-attack.
The suspension, which lasted more than four hours starting at 15:54 EST (19:54 GMT) on Friday, was the longest such incident since the 11 September 2001 attacks. The fallout continued into Saturday, with tracking website Flight Aware reporting over 3,500 cancellations and more than 2,000 delays.
Passengers faced significant difficulties, with some remaining trapped on tarmac-bound aircraft, while authorities allowed certain international flights to depart in an attempt to manage airport congestion.
Former TSA Administrator John Pistole noted that while the system's restoration in four-and-a-half hours demonstrated resilience, questions remain regarding long-term stability. Secretary Duffy warned that similar issues could recur unless Congress approves necessary upgrades to air traffic control infrastructure.
President Donald Trump has requested $30.1bn for these improvements, a proposal currently pending before a Congress controlled by the Republican Party.
