A nationwide ground stop that led to thousands of flight cancellations across the United States was triggered by an issue following a copper wire upgrade, according to Transport Secretary Sean Duffy. The disruption, which began on Friday, was the longest such incident since the 11 September 2001 attacks, and its effects are expected to linger for days.

Cause Under Investigation

Speaking at a news conference, Duffy explained that the government is investigating whether the problem stemmed from incompetence by the contractor performing the upgrades or from faulty equipment. He emphasized that there is no indication of a cyber-attack, though the inquiry is ongoing.

The maintenance work, aimed at replacing copper wire with fibre, was being carried out by L3Harris, a technology provider. Duffy noted that the US telecommunications system is incredibly old, and the copper wire being discontinued was outdated. During the upgrade, a router that was being worked on began flooding other air traffic control systems, causing communication issues with aircraft. This prompted the government to shut down the airspace for safety reasons.

Bryan Bedford, head of the Federal Aviation Administration (FAA), echoed Duffy's sentiments, stating at the same conference: "We see zero evidence of anything nefarious, and zero evidence of anything AI related."

Massive Disruption

No flights were permitted to take off from the continental US for over four hours, from 15:54 EST (19:54 GMT) on Friday. According to tracking website FlightAware, more than 3,500 flights were cancelled and over 2,000 delayed on Saturday as knock-on disruption continued. In some cases, passengers were stranded on planes on the tarmac, unable to take off or return to the gates. Some international flights were allowed to depart in an apparent effort to free up space.

Duffy cautioned that a similar issue could occur again unless Congress approves upgrades to air traffic control infrastructure. US President Donald Trump has requested $30.1bn for these upgrades, and both chambers of Congress are currently controlled by the Republican Party.

Questions Remain

Former TSA Administrator John Pistole told the BBC that the fact the system was restarted in four and a half hours is good news, demonstrating resilience. However, he questioned: "What's to say it's not going to happen tomorrow?" This marks only the second nationwide ground stop since the days following the 9/11 attacks.