At a press conference today, Transportation Secretary Sean Duffy said that Friday’s nationwide ground stop ordered by the FAA was related to work replacing outdated copper wire with a fiber optic line at a “remote FAA facility.” The secretary said that this was “routine maintenance,” rather than the result of a major modernization effort. He told reporters that it was “such an old wire that it was being discontinued, meaning that line was going to get shut down,” necessitating the upgrade.

What wasn’t clear, according to Secretary Duffy, was the root cause of the problem. He said that it could have been faulty hardware, a misconfigured router, or “incompetence” on the part of contractor L3Harris. Regardless, what followed was the newly installed router “flooding” other routers in the Air Traffic Control system. Duffy said that there were “over 1,000 connection attempts every 4 to 5 seconds,” causing disruption to radar feeds and communication with planes.

Secretary Duffy also took the opportunity to call on additional funding from Congress for modernizing the Air Traffic Control system, and to tout the work the FAA has done so far. “We are building, we are building safely, but we are building fast,” he said, but said that Congress had only given him a “partial payment” to complete the necessary work.

In a statement posted to their site, L3Harris said:

L3Harris has been modernizing the communications infrastructure supporting the National Airspace System in close coordination with the FAA. With safety and reliability as our highest priorities, L3Harris, together with its telco partners and the FAA, has completed more than 70% of the planned airspace communications conversion from legacy copper wires to a fiber optic system. We are supporting the FAA in its investigation to understand the conditions that led to the Nov. 13 ground stop of our nation’s air travel. L3Harris takes the nationwide ground stop and its impact on travelers, airlines and air traffic operations seriously.

Update November 14th: Added a statement from L3Harris.