FAA Router Overload from L3Harris Cable Upgrade Grounded 8,200+ Flights

More than 8,200 flights were canceled on Friday evening, and at least 3,000 more on Saturday, after a router installed during an L3Harris cable upgrade overloaded a critical Federal Aviation Administration communication system and forced a nationwide ground stop — only the third such halt of the 21st century.

Transportation Secretary Sean Duffy told reporters on Saturday that the failure originated in what he described as routine maintenance at a remote location: L3Harris, a longtime FAA contractor, was replacing copper wire with fiber optic cable. After the switchover, a router overloaded the system that carries air traffic communications, and the FAA halted departures across the United States.

Duffy said the investigation now turns on the contractor's work. "What we're working to determine was whether we had incompetence — meaning, was it user error or installator error from L3Harris? Or did they install a faulty router?" he said at a Saturday press conference.

The FAA's acting CTO, Rebecca Guy, described the failure mechanism in detail: as the network became unstable, engineers traced the problem to two devices hammering the system with traffic. "We saw two places that were actually pinging our network at a very high rate — a thousand connections over every four to five seconds," Guy said.

Engineers disabled both sources immediately. "We were able to stabilize our network," Guy said, and the agency is now performing a root cause analysis.

The scale was unusual. A nationwide ground stop — every departure in US airspace held at once — has happened only twice before this century. Aviation data firm Cirium counted more than 8,200 canceled flights on Friday evening alone, with at least another 3,000 scrubbed on Saturday as the recovery continued even after the ground stop was lifted.

Why was the work done on a Friday afternoon?

Duffy faced questions about why the switchover happened at 3pm on a Friday rather than overnight, when traffic is light. His answer drew a distinction between facility types: "switchovers" at bigger airports take place late at night, he said, but work at remote sites is scheduled during the day.

"It's pretty straightforward work that we were doing yesterday at, again, a very remote location," Duffy said. He added that the timing policy will change: "There will be reevaluation of when we do this work."

The secretary has used multiple press conferences this week to press Congress for more funding to upgrade aging aviation equipment, and the incident gave that argument new force.

Was AI involved?

The timing raised eyebrows in Washington. The ground stop came one day after the FAA announced the rollout of an AI tool for air traffic controllers — a rollout the air traffic controllers union said it was not consulted on during design.

FAA administrator Bryan Bedford shut down that line of speculation directly. The agency sees "zero evidence of anything nefarious and zero evidence of anything AI-related," Bedford said. "We want to be clear that we have an equipment issue, and we're working through what this defective piece of equipment was."

Homeland Security Secretary Markwayne Mullin, asked earlier whether AI caused the outage, offered a blunter dismissal: "We call it SI around here, remember? SI."

Notably, the Saturday press conference itself suffered technical issues, an irony visible on the broadcast.

What happens next?

Three threads remain open:

• Root cause analysis. The FAA is determining whether the router itself was defective or the installation was botched — the distinction that will decide where liability with L3Harris falls.
• Scheduling reform. The FAA will reevaluate when remote-site switchovers occur, after the Friday-afternoon timing amplified the disruption.
• Funding pressure. Duffy continues to push Congress for appropriations to modernize FAA infrastructure, arguing the copper-to-fiber transition is part of a broader, overdue upgrade program.

The takeaway in plain terms: a routine copper-to-fiber cable swap, performed at a single remote facility by an experienced contractor, was enough to stop every commercial departure in the United States for hours.