Faulty Router Upgrade Grounded U.S. Flights, Canceling Over 11,000 Trips

A routine copper-to-fiber upgrade triggered the third nationwide ground stop of the 21st century, canceling more than 8,200 flights on Friday evening and at least 3,000 more on Saturday, according to aviation data firm Cirium.

Transportation Secretary Sean Duffy said Saturday that contractor L3Harris, a longtime Federal Aviation Administration vendor, was upgrading copper wire to fiber optic cable at a remote location. After the work, a router overloaded a critical communication system and forced the ground stop.

"It's pretty straightforward work that we were doing yesterday at, again, a very remote location," Duffy said at a Saturday press conference. "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?"

What disabled the network?

The FAA's acting CTO, Rebecca Guy, described the failure mechanism at the same briefing. When the network became unstable, engineers traced the traffic and found the source.

"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.

The FAA disabled both endpoints immediately. Guy said the agency "were able to stabilize our network" and is now performing a root cause analysis. The question of fault now narrows to a single machine: the router L3Harris installed, or the way it was installed.

Why did the work happen on a Friday afternoon?

Reporters pressed Duffy on the timing. The switchover ran at 3 p.m. on a Friday, not in a quieter window such as midnight on a Saturday. Duffy said bigger airports will get their switchovers late at night, but remote sites are switched during the day.

"There will be reevaluation of when we do this work," he said.

Duffy has used multiple press conferences this week to press Congress for more funding to upgrade aging aviation equipment. The outage gives that argument fresh force: one router at one remote site halted the entire national air traffic system.

Was AI involved?

No, according to the FAA's leadership. The ground stop landed one day after the FAA announced an AI tool for air traffic controllers, and the controllers union said it was never consulted in designing that system. The timing invited speculation.

FAA administrator Bryan Bedford shut it down. He said the agency sees "zero evidence of anything nefarious and zero evidence of anything AI-related."

"We want to be clear that we have an equipment issue, and we're working through what this defective piece of equipment was," Bedford said.

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

What happens next?

The FAA's root cause analysis will determine whether L3Harris made an installation error or supplied a faulty router. Either answer carries cost and accountability questions for one of the agency's longest-serving contractors. Saturday's press conference, which itself suffered technical issues, ended with Duffy promising a review of maintenance scheduling — meaning the timing of remote switchovers, not just the hardware, is now on the table.