A botched fiber optic installation by an L3Harris contractor triggered a nationwide ground stop on Friday night, and Transportation Secretary Sean Duffy says the FAA cannot replace the company until Congress approves new funding.

Duffy told a press conference at the Department of Transportation on Saturday that the halt stemmed from work switching telecommunications lines from aging copper wire to fiber optic cable. The copper line was being discontinued, forcing the transition.

"The work happening was due to the age of the copper wire that we were replacing," Duffy said. "It was such an old wire that it was being discontinued, meaning that line was going to get shut down, so we had to switch it over from old copper."

When the contractor installed the new router, the technology appeared to overload the air traffic control system, prompting officials to ground all flights.

"We had over 1,000 connection attempts every four to five seconds, and what that did was give us issues with our communication with airplanes, and it also caused some disruption with our radar feeds," Duffy said.

What caused the outage?

FAA administrator Bryan Bedford said the fiber installation error did not cause a blackout in the FAA Telecommunications Infrastructure. Instead, facilities reported frequencies cutting in and out.

"What we had were random reports from different facilities of certain frequencies that were going in and out, and requiring them to switch between primaries and backup switching," Bedford said. "Now, if that had been a single facility, we would have just worked through it. But when we saw it go to two, three, 10, 17 facilities, that's when we started to realize there was something much larger going on here. And since we couldn't explain it quickly, that's when we went to the national ground stop."

Investigators are now determining whether the fault lies with the contractor or the equipment itself.

"What we're working to determine was whether we had incompetence, meaning was it user error or installation error from L3Harris, or did they install a faulty router?" Duffy said. "We haven't determined what the fault was."

Both officials ruled out hostile explanations. Duffy said "we don't believe" the error resulted from a cyberattack, and Bedford said there is no indication artificial intelligence was involved.

Why is the FAA tied to L3Harris?

L3Harris has served as the FAA's major technology integrator and managed-service provider for more than 20 years, and it remains the sole provider on the current network. Duffy said additional funding would let the agency move on.

"With our new architecture, with the money that we're requesting, we will work with the greatest telecom companies in the world, which will be AT&T, Verizon, and Lumen," he said. "They're all working with us on the new architecture. But in the meantime, until I can build that, I'm stuck with L3Harris, who owns this network."

Duffy tied the incident directly to decades of underinvestment and his long-running funding requests.

"This was an FAA system that didn't meet the moment," he said. "Our contractor didn't meet the moment, or the equipment didn't meet the moment, and caused the outages. I've been talking about this for almost two years, and I've been asking Congress for money."

How much money is on the table?

Congress has already approved $12.5 billion for air traffic control modernization through Trump's One Big Beautiful Bill Act, but Duffy said that initial investment falls short. President Donald Trump previously requested $30 billion for the effort; Duffy raised the ask to $50 billion on Friday to complete the overhaul.

Despite the funding gap, modernization is underway. Duffy said 69% of copper communication wires have already been updated with fiber, among other efforts.

"We can't continue on technology of the [1980s]," Duffy said. "I mean, we spend over $200 million a year in obsolescence fees. We have to pay to use these old copper wires. We have to get off of them. They're less reliable. So we have to make the transition, and we're making the transition not because we want to spend money. We're making the transition because it's safer and it's more resilient."

When will flights return to normal?

Bedford said Saturday would remain disrupted, with thousands of cancellations, but a full recovery is expected by Sunday's close of business.

"We do anticipate somewhere between four and 5,000 of the 41,000 flights that are scheduled today likely will cancel, so we will still have delays and cancellations today," Bedford said. "But that will set us up for a full recovery tomorrow. And based on everything that we're hearing from our airline partners, they believe that they'll be able to have full schedule integrity by the close of business on Sunday."

The outage puts fresh pressure on a modernization program already under scrutiny.