What Caused the US FAA Ground Stop and How Did a Copper-To-Fibre Switch Disrupt Flight Radar Feeds?

A contractor's work replacing copper telecommunications lines with fibre may have triggered the US Federal Aviation Administration's (FAA) ground stop on Friday, 13 November. Transportation Secretary Sean Duffy said investigators were examining whether contractor error or a faulty router disrupted communications and radar feeds. The exact fault has not been confirmed.

The ground stop was lifted after more than four hours, but the disruption carried on into Saturday, 14 November. FlightAware data showed 3,374 US flights cancelled by early Saturday morning.

Duffy said the problem began during routine maintenance at a remote FAA site. He named L3Harris Technologies, the FAA's long-time telecommunications contractor and the operator of its network, as the company carrying out the work.

How the Contractor's Network Upgrade May Have Triggered the Outage

According to Duffy, a router involved in the copper-to-fibre switch started flooding other routers across the air traffic control network. 'We had over 1,000 connection attempts every four to five seconds,' he said.

The network carries radar data and voice communications between FAA facilities, allowing controllers to monitor aircraft and communicate with pilots. As the connection attempts overwhelmed the network, controllers experienced inconsistent radar data and difficulties communicating with aircraft. A senior government official later told NBC News the system behind the outage had been identified and taken offline.

Investigators are examining whether the incident resulted from 'user error or installer error' or faulty equipment, Duffy said.

The FAA has been replacing old copper lines with fibre, 5G wireless and low-Earth-orbit satellite links. FAA Administrator Bryan Bedford told lawmakers in September that over 64 per cent of the copper-based network had been replaced by 1 September. Duffy put the figure at 69 per cent on Saturday.

Homeland Security Secretary Markwayne Mullin said officials had found no sign of an attack but were not ruling one out. 'There's nothing completely certain right now. It doesn't appear that way,' he said.

Duffy said officials did not believe a foreign nation had attacked the network.

Flight Disruptions Spread Across the US and Canada

Controllers first noticed the inconsistent radar and communications data at 3.36pm Eastern time on Friday, according to Duffy. The FAA issued the ground stop at 3.54pm and lifted it at 8.15pm. About 3,500 aircraft were airborne, and officials said all of them landed safely.

The effects reached beyond US airports. Canadian Transport Minister Steven MacKinnon said Canada's air traffic systems were operating normally but warned that travel to the US could be disrupted. He said Canada had offered the FAA its 'full assistance', including room for US-bound aircraft.

Toronto Pearson said flights to and from the US would keep facing disruptions and cancellations even after the ground stop ended. Air Canada cancelled all its US flights for the rest of Friday evening and said the impact would continue into Saturday. Passengers were told to check with their airlines.

Bedford said he expected US air travel to return to normal by the end of Sunday, 15 November. Duffy was more cautious, saying delays and cancellations would continue as carriers 'reposition aircraft/crews where they are needed most'.

The harder questions are still open. Investigators have yet to explain how one router produced enough traffic to unsettle control centres across the country. Until investigators establish the precise cause, contractor error and faulty equipment remain possible explanations rather than confirmed findings.