US flights grounded: Inside the 4-hour FAA outage that cancelled 7,000+ flights

The United States Federal Aviation Administration (FAA) lifted a nationwide ground stop Friday, November 13, after a communications failure at air traffic control centres disrupted flights across the country, forcing departing aircraft to remain on the ground for more than four hours.

The shutdown began at 3:54 pm Eastern Time (2:24 am IST on November 14) and was lifted at 8:15 pm ET (6:45 am IST), according to Transportation Secretary Sean Duffy. Although flights began resuming, airlines warned that the disruption could continue for days as aircraft and crew members were left out of position.

How did a communications failure bring flights across the US to a halt? What went wrong inside the air traffic control network, and why did the disruption continue after the FAA reopened the airspace? Our interactive graphic takes you through the shutdown, scene by scene, explaining what happened, why it happened and what comes next.

More than 2,500 flights were cancelled in the United States on Saturday, with hundreds more delayed, news agency Associated Press reported. On Friday, over 4,700 flights were cancelled and around 10,000 delayed, news agency Reuters reported, citing FlightRadar24 figures.

The incident was the second nationwide ground stop since the September 11, 2001, attacks, the report added. It has also renewed scrutiny of the ageing technology used to manage US air traffic and the challenges facing the government's modernisation programme.

The trouble began around 3:36 pm ET on Friday, when air traffic control centres experienced instability in radar and communications systems, Duffy said. These facilities coordinate aircraft travelling between different parts of the country.

The problems also affected Terminal Radar Approach Control facilities, or TRACONs, which manage aircraft approaching and departing airports. Duffy said controllers began receiving inconsistent data from older switches and routers.

Although communications and radar capabilities were not completely lost, the instability made it difficult for controllers to reliably communicate with pilots and track aircraft. The FAA issued a nationwide ground stop at 3:54 pm ET, directing departing flights to remain on the ground until further notice.

The agency described the decision as necessary under extraordinary circumstances and for safety reasons. More than 3,500 aircraft were in the air when the disruption began, Duffy said. Aircraft already airborne were allowed to continue to their destinations and land safely.

International departures were handled on a case-by-case basis. The restrictions also affected international aviation. The European aviation agency suspended US-bound departures from its member states at the FAA's request for several hours.

Some flights across the Pacific, including those heading to Hawaii and Asia, were subsequently cleared to depart from San Francisco International Airport, according to the Associated Press. At 8:15 pm ET, Duffy announced that US airspace had reopened.

However, he warned that flights would resume gradually, depending on the availability of aircraft, pilots and flight attendants. "It's going to be slow," Duffy told reporters, urging passengers to check directly with their airlines.

The Trump administration blamed the outage on ageing air traffic control equipment that became overloaded as new technology was being integrated into the existing network. Duffy said older switches and routers were overwhelmed by data, resulting in inconsistencies in the information reaching air traffic controllers.

"Our switches, our routers actually got overloaded with data and they started to give us inconsistencies in the data from those routers and because of that we shut the system down," Duffy said, according to Reuters. He said the system had not suffered a complete loss of radar or communications and that controllers had been able to land aircraft safely.

Homeland Security Secretary Markwayne Mullin said the introduction of new technology and security patches into the older network appeared to have overwhelmed parts of the system.