FAA Ground Stop Cause Revealed: L3Harris Router Flooded Air Traffic Control Network

A routine equipment upgrade went wrong on Friday, November 13, and brought American air travel to a standstill. The Federal Aviation Administration has now said the nationwide ground stop was caused by a router installed by its contractor L3Harris, which began flooding the air traffic control communications network with repeated connection attempts during a switch from old copper wiring to fibre optic lines.

Transportation Secretary Sean Duffy explained the failure at a news conference on Saturday, a day after the FAA ordered nearly all departing flights across the United States to stay on the ground. Officials have ruled out a cyberattack, and the precise fault — whether an installation error or a defective router — is still under investigation.

What happened on Friday

Controllers began seeing unstable radar and communications data at 3:36 p.m. Eastern Time on Friday, according to Duffy. The FAA issued a nationwide ground stop at 3:54 p.m., citing a telecommunications outage affecting air route traffic control centres. Aircraft already in the air were allowed to continue to their destinations, and more than 3,000 flights landed safely while the order was in force. The stop was lifted at 8:15 p.m., after more than four hours.

It was only the second nationwide ground stop since the attacks of September 11, 2001, and the first since January 2023, when a computer failure in the system that sends safety notices to pilots halted departures. News agency reports described Friday's stop as the longest in 25 years.

How one router grounded the country

L3Harris, the FAA's long-time communications contractor, was carrying out routine maintenance at a remote facility on Friday afternoon, replacing a section of the air traffic control system's old and discontinued copper wire with new fibre optic lines. The new router installed during that work then started overloading the system.

"We had 1,000 connection attempts every four to five seconds," Duffy told reporters. The faulty equipment flooded other routers across the network, causing intermittent communications and radar gaps at 17 of the FAA's 22 en route centres, which manage aircraft travelling between airports. Because officials could not immediately locate the source of the overload, they grounded flights nationwide as a safety precaution.

"When we see that, your safety is paramount. We shut down the airspace," Duffy said.

The union representing FAA safety employees, the Professional Aviation Safety Specialists, said the problem was isolated to two routers that were updated on Friday. An official told Reuters the routers were believed to be in Arkansas and Texas. Once technicians isolated the work being done at that location, the systems came back online.

Not a cyberattack, officials say

The sudden halt initially raised fears of a cyberattack, and White House officials convened an emergency meeting in the Situation Room on Friday. The government has since said it does not believe that was the cause.

"Once we were able to isolate the work being done at this location, all of our systems came back online," Duffy said. "So we don't believe this was cyber at all."

FAA Administrator Bryan Bedford repeated that view on Saturday. "We see zero evidence of anything nefarious and zero evidence of anything AI-related," he said.

The weekend fallout

Lifting the ground stop did not restart the schedule. Airlines spent the weekend moving displaced aircraft and crews back into position, and cancellations piled up through Saturday.

About 9,200 flights were cancelled and 7,500 delayed on Friday, according to aviation tracking site FlightAware. By 9:35 p.m. Eastern Time on Saturday, airlines had cancelled more than 6,400 US flights and delayed more than 8,000. Another 875 flights scheduled for Sunday had already been cancelled by Saturday night.

Bedford said about 12,000 flights were lost in total, including roughly 9,000 commercial flights and 3,000 private flights, leaving crews and aircraft out of position. "We have crews and aircraft that are out of position for 12,000 flights that were lost," he said. "These crews, pilots and flight attendants need to get to their points of reconnection with their schedules."

Both Duffy and Bedford said airlines were expected to restore full schedules by late Sunday. "I do think the worst is behind us," Bedford said. Tens of thousands of passengers were left stranded at airports across the country, and airlines issued travel waivers allowing affected passengers to rebook at no cost.

Who is responsible — and what happens next

Duffy said investigators are still determining exactly what went wrong. "What we're working to determine was whether we had incompetence, meaning was it ... installator error from L3Harris? Or did they install a faulty router?" he said. "We haven't determined what the fault was."

He was blunt about the contractor's performance. L3Harris "didn't meet the moment," Duffy said, adding: "They own this network. They're our prime contractor. I can't go somewhere else. They own it. Frankly, we're going to hold people accountable."

L3Harris said it is supporting the FAA's investigation and takes the ground stop seriously. The company said it has been modernising the communications infrastructure supporting the National Airspace System in close coordination with the FAA, and has completed more than 70 percent of the planned conversion from legacy copper wires to a fibre optic system. The FAA said it is doing additional testing with L3Harris to check for any further risks.

Democrats in Congress have also begun pressing for accountability, launching oversight efforts into the disruption and the administration's handling of the ageing system.

An ageing system under strain

The incident has renewed attention on the age of America's air traffic control infrastructure. The routers being replaced in the latest upgrade were about 25 years old and were originally supposed to have been replaced in 2006, according to Duffy. The FAA spends around 1 billion dollars a year maintaining its old copper-wire telecommunications network while it works to move to fibre.

Congress approved 12.5 billion dollars for air traffic control upgrades in 2025. Duffy on Friday called for 50 billion dollars in funding to modernise the systems, up from his earlier request of 30 billion dollars. Bedford warned that the ageing technology "will continue to break until we replace it."

For passengers, the disruption came just before a busy week of travel ahead of the Thanksgiving holiday. The investigation into the router failure continues, and the FAA has not said when its findings will be published.

Related reading: Wall Street Ends a Turbulent Week Mixed: S&P 500 and Nasdaq Slip Friday

Sources

• Al Jazeera — What forced the US to ground all planes? A router switch, we now know
• Reuters via ThePrint — US air travel disruptions to persist until late on Sunday, FAA head says
• CNN — What we know about the cause of the nationwide FAA ground stop
• USA Today — Democrats seek accountability for nationwide aviation ground stop
• CNBC TV18 — US aviation shutdown: How an L3Harris-installed router disrupted thousands of flights across America
• The Manila Times (AP) — US air travel should normalize Sunday after ground stop triggers mass cancellations, FAA says