FAA lifts longest nationwide flight ground stop since 9/11 after communication overload

The U.S. Federal Aviation Administration (FAA) ended a four-hour nationwide ground stop on Friday, the longest such interruption since the September 2001 attacks. The agency said the stoppage was caused by "extraordinary circumstances" stemming from a communication issue that affected all air-traffic-control centres.

Flight tracking data showed more than 8,500 flights were delayed and nearly 8,000 cancelled. At the time of the halt, about 3,500 aircraft were airborne; some were diverted while others continued to their destinations. The FAA reopened the skies at 20:15 EST after allowing limited departures from San Francisco International Airport.

International traffic was also impacted. Eurocontrol reported that U.S.-bound flights from its 42 member states were suspended at the FAA's request, and Sydney Airport halted all U.S.-bound services. Air Canada cancelled cross-border flights between the United States and Canada.

Transportation Secretary Sean Duffy told a news conference that the outage would create a ripple effect for several days, saying, "It's going to take us some time to unwind what's happened this afternoon." He added that a legacy analogue telecom system had become overloaded, causing switches and routers to fail and affecting communications and radar. Duffy estimated a complete overhaul of the system could cost around $50 billion.

Homeland Security Secretary Markwayne Mullin said officials found "zero evidence" of a cyber-attack and ruled out any connection to the recent global Microsoft outage. Mullin noted that the introduction of new technology into the old system had overwhelmed it, but affirmed that the public was never in danger during the incident.

The stoppage was the second nationwide ground stop since the immediate aftermath of the 9/11 hijackings. Dr. Guy Gratton, an associate professor of aviation at Cranfield University, described it as "the worst since 9/11, but clearly not on that scale."