Duffy Traces Nationwide FAA Ground Stop to Router Overload After L3Harris Fibre Work

"It's pretty straightforward work that we were doing yesterday at, again, a very remote location," Duffy said at a press conference that appeared to have technical issues of its own. Investigators are still trying to establish who or what was at fault. "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.

The explanation matters because the ground stop came a day after the FAA announced the rollout of an AI tool for air traffic controllers. The controllers' union said it had not been consulted in designing the system. FAA Administrator Bryan Bedford said the agency saw "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 had been asked earlier whether AI caused the ground stop. "We call it SI around here, remember? SI," he replied.

Rebecca Guy, the FAA's acting chief technology officer, said engineers began looking for a cause once the network became unstable. "We saw two places that were actually pinging our network at a very high rate," she said, describing a thousand connections every four to five seconds. The FAA disabled "both of those, right away and were able to stabilize our network," Guy said. The agency is now carrying out a root cause analysis.

Duffy was asked why the upgrade was done at 3 p.m. on a Friday rather than late at night. He said switchovers at bigger airports take place late at night, but remote switchovers happen during the day. "There will be reevaluation of when we do this work," he said.

It was only the third nationwide ground stop of the 21st century. Aviation data firm Cirium counted more than 8,200 flights cancelled on Friday evening. The disruption continued after the ground stop was lifted, with at least another 3,000 flights cancelled on Saturday.

Duffy has repeatedly said at press conferences that Congress needs to provide more money for aviation equipment upgrades.