A single router installed by government contractor L3Harris Technologies may have caused the longest nationwide ground stop of US flights in 25 years, officials said on Saturday, a day after the shutdown left travellers stranded across the country.
The Federal Aviation Administration (FAA) halted flights for more than four hours on Friday, with some domestic take-offs resuming around 8:15 pm ET, after the equipment overloaded part of its air traffic control system. FAA administrator Bryan Bedford said the “worst is behind us” and expects airline schedules to recover fully by the end of Sunday, ahead of the Thanksgiving travel rush.
Transportation Secretary Sean Duffy said a contractor was swapping a section of old copper wire for fibre cabling at a remote location on Friday afternoon when the router began overloading the system. He said the new routers flooded others with more than 1,000 connection attempts every four to five seconds, causing intermittent disruption to communications and radar feeds at 17 of the FAA’s 22 en route centres. Unable to find the cause quickly, officials grounded flights nationwide. Bedford later apologised to stranded travellers, saying the stoppage was ordered out of caution and that the system was operating safely.
Officials said routers installed in both Arkansas and Texas may have been at fault. Duffy said officials were working to determine whether L3Harris staff made an error or installed a faulty router, but no cause had yet been established. “Our contractor didn’t meet the moment or the equipment didn’t meet the moment,” he said.
L3Harris said it was supporting the FAA’s investigation and took the impact on travellers, airlines and air traffic operations seriously. The company added that it had completed more than 70 per cent of the planned conversion of airspace communications from copper to fibre.
The union representing FAA technicians, the Professional Aviation Safety Specialists, said the agency normally asks its own technicians to assess the risks of upgrades or repairs beforehand, but that did not happen this time.
Homeland Security Secretary Markwayne Mullin said there was no sign the failure was linked to a cyberattack and that no lives were at risk. Duffy said more than 3,000 aircraft in the air when the order was issued landed safely. Federal officials and a Microsoft spokesperson also said the stoppage was unrelated to a Microsoft outage on Thursday, which the company said had been fully resolved.
Bedford said about 12,000 scheduled flights could not take off on Friday. Of 41,000 flights scheduled for Saturday, more than 6,400 had been cancelled by evening, according to FlightAware, which also reported more than 800 cancellations for Sunday.
Aviation consultant Andrew Charlton said the stoppage affected about a quarter of the 45,000 flights operated in the US each day. The knock-on effect was huge, he said, because aircraft rarely make a single round trip but hop from city to city, a problem magnified on long-haul and international routes.
Passengers scrambled to reach their destinations, with some waiting out the chaos in hotels, others racing to secure rental cars or bus and train tickets, and many camping in airports. Dan Russell, 66, learned his connecting flight from Hawaii to California was cancelled half an hour before boarding in San Diego on Friday night. With hotels full, he and his wife waited at the airport. Sports teams adjusted game start times, and No. 19 Mississippi’s football game at Oklahoma was pushed to Sunday.
Airlines must offer free rebooking or a full refund when a flight is cancelled, and Bedford said the administration was working with carriers, which were waiving all terms and conditions. Some let passengers with travel booked for Friday or Saturday rebook, while others extended the offer to Sunday or even Monday. Bedford urged passengers to contact their airlines.
Friday’s stoppage was the first nationwide since January 2023, when a malfunction in an FAA computer system that sends notices to pilots grounded flights, and only the second since the September 11, 2001 attacks. That 90-minute episode disrupted 11,000 flights and was caused by a government contractor unintentionally deleting files, Reuters reported.
Ageing equipment was also blamed for brief radar outages that disrupted Newark airport last year. Officials said the system will fail again until it is properly upgraded.
The routers being replaced were about 25 years old and due to be swapped out in 2006, Duffy said. The overhaul began last year with $12.5 billion from Congress, and about 70 per cent of the copper wire has been switched to fibre. Duffy and the White House are seeking a further $30 billion, with administration officials blaming Congress for not approving more. Duffy said work at smaller facilities would be reassessed to avoid future disruption. President Donald Trump has not commented publicly.
