The hourslong halt to departing flights across the country on Friday started with routine maintenance on air traffic control equipment at a remote site, federal officials said on Saturday.
That work was being carried out by L3Harris Technologies, a little-known defense contractor that owns and operates essential communications infrastructure used by the Federal Aviation Administration.
Transportation Secretary Sean Duffy stopped short of saying that the company was at fault, but he vowed to investigate whether it bears responsibility.
“What did L3Harris do? Did they make mistakes yesterday?” he said at a news conference on Saturday. “They own this network. They’re our prime contractor. I can’t go somewhere else. They own it. Or was it a faulty router? And we’re going to find that out. And frankly, we’re going to hold people accountable.”
In a statement on Saturday, L3Harris said that it was supporting the F.A.A. investigation into what had happened and that it “takes the nationwide ground stop and its impact on travelers, airlines and air traffic operations seriously.”
The company was formed in 2019, the result of a merger of two defense contractors. It employed about 45,000 people at the start of this year and is based in Florida.
About 75 percent of its revenue comes from U.S. government contracts, many of them for the military. In 2025, the company was selected to retrofit a Boeing 747 donated by Qatar to be used as the interim Air Force One. L3Harris has generated more than $1 billion in annual profits since 2020.
The company also does a lot of work for the F.A.A., including maintaining networks that facilitate communications between air traffic controllers and pilots and receive plane location signals.
L3Harris owns the equipment used to transmit voice communications and data to and from air traffic control facilities, remote radar sites and weather stations, a network known as the F.A.A. Telecommunications Infrastructure. The company is in the midst of upgrading the copper wires used in that network to high-speed fiber optic cable across more than 4,400 sites, with over 70 percent of those lines already replaced.
Federal officials said on Saturday that they had halted departing flights a day earlier because of a communications disruption set off by a copper-to-fiber upgrade at a remote site, which they did not identify. A newly installed router began firing more than a thousand connection requests every few seconds, which disrupted voice communications and radar feeds. Ultimately, it took technicians 45 minutes to identify the problem.
The F.A.A. is trying to build a modern replacement to its telecommunications network with other partners, including AT&T and Verizon, over the next few years, Secretary Duffy said on Saturday. “Until I can build that, I’m stuck with L3Harris,” he said.
