The system that brought air travel to a standstill on Friday is an outdated network of wires, cables and network gear which carry the radio transmissions, radar data and text messages that enable safe navigation.
Thousands of air-traffic controllers rely on the network to guide pilots flying through invisible slices of the nation's airspace.
Officials from the Transportation Department and Federal Aviation Administration on Saturday blamed problems that emerged within that communications backbone as the reason for halting nearly all departures across the country for more than four hours. Defense contractor L3Harris Technologies oversees that system, known as the FAA Telecommunications Infrastructure, or FTI.
Federal officials said it wasn't yet clear whether problems with a newly installed router or errors by L3Harris triggered Friday's air-traffic meltdown.
An L3Harris spokeswoman said the contractor has so far upgraded about 70% of the FAA's aging copper-based network and is supporting the agency's probe into what went wrong Friday.
"L3Harris takes the nationwide ground stop and its impact on travelers, airlines and air traffic operations seriously," the company said in a statement.
What's the issue with FTI?
The FTI network has suffered repeated failures in recent years as officials struggle to replace it with a modernized network based on fiber-optic cables and newer routing hardware. But efforts to maintain and replace the mission-critical network have taken years and become more expensive over time.
The older copper-wire system has a limited capacity to carry data, while the new fiber links move information more quickly. If data from the newer system overloads the older system, it can throw transmissions out of sync and cause disruptions, industry officials said.
The risks that FTI failures posed to the FAA's air-traffic system are well known. A 2023 outside review warned that "system risk could quickly reach unacceptable levels" due to increased network outages and inadequate funding for overhauls.
Communications failures have been severe in recent years. In September, the accidental cut of a backup fiber-optic line, along with the failure of a primary circuit, snarled air traffic throughout the Northeast.
What is the role of L3Harris?
L3Harris has served as a prime contractor on the FTI since 2002. Part of the dedicated network connects about 1,000 locations across the nation's airspace system. Its contract requires the company to restore vital communications services to some sites within three hours of an outage, according to a 2022 contract notice.
"What did L3Harris do?" Transportation Secretary Sean Duffy said at a press conference. "Did they make mistakes yesterday? 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."
Where is the FAA on its yearslong replacement of the aging network?
Some of the network upgrade work runs through a yearslong project known as FENS, or FAA Enterprise Network Services. The U.S. government awarded Verizon a $2.4 billion contract in 2023 to support the overhaul. AT&T later took over as lead contractor on the upgrade project.
A Verizon spokesman said it remains an FAA partner, but much of its former contract work is undertaken by other service providers. An AT&T spokeswoman said that the company's network was working normally.
Duffy on Friday made a plea for Congress to provide around $50 billion for upgrades to the nation's air-traffic control communications systems and infrastructure to avoid similar issues from happening in the future.
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