A router overloaded the U.S. air traffic control network after L3Harris replaced copper wiring with fiber optics at a remote FAA facility. The failure led to a nationwide flight stoppage on Friday, November 13, leaving thousands of flights canceled or delayed while the agency investigated what went wrong.
A wiring conversion led to a nationwide stoppage
Transportation Secretary Sean Duffy explained on Saturday that the work involved replacing an old copper line with a fiber connection at a remote Federal Aviation Administration (FAA) site. The copper line was going to be retired, so the change had to be completed. Duffy described it as routine maintenance, not a major modernization effort.
The problem arose after the replacement: the new router generated an abnormal volume of connections that affected other equipment in the air traffic control system. According to Duffy, the resulting traffic disrupted radar signals and communications with aircraft. The FAA ordered flights to stop nationwide for about four hours on Friday.
“What we’re trying to determine is whether there was incompetence—that is, whether it was a user error or an error by the L3Harris installer—or whether they installed a faulty router.”
— Sean Duffy, Transportation Secretary
Rebecca Guy, the FAA’s acting chief technology officer, said the agency detected two points with a thousand connections every four or five seconds. It disabled them immediately and managed to stabilize the network. The FAA was conducting a root-cause analysis, but had not determined whether the source was a faulty router, an incorrect configuration, or an installation failure.
Investigation points to equipment but does not establish the cause
Duffy attributed the work to L3Harris, a longtime FAA contractor. In his remarks, he raised several possibilities: user error, an installer failure, or the contractor having installed faulty hardware. The investigation was to establish which of those explanations, if any, described the specific failure.
The company said it is working with the FAA to modernize the communications infrastructure supporting the National Airspace System. L3Harris said that, together with its telecommunications partners and the agency, it has completed more than 70% of the planned conversion from legacy copper cables to a fiber-optic system. It added that it is cooperating with the investigation into the circumstances that led to the November 13 stoppage and takes its impact on passengers, airlines, and air traffic control operations seriously.
Duffy said this type of replacement has been carried out for decades at U.S. institutions and that the FAA continues to use old equipment because the necessary investments have not been made. At the same time, he defended the pace of improvements and again called on Congress for more funding to upgrade air traffic control systems.
The timing of the change will also be reviewed
The work was carried out at around three o’clock on Friday afternoon, prompting reporters to ask why it had not been scheduled overnight or over the weekend. Duffy replied that changes at large airports are made late at night, but replacements at remote locations are done during the day. He also said the FAA would reassess when it carries out this type of work.
The secretary said Congress had provided only partial funding to complete the necessary upgrades and called for additional resources. In July 2025, Congress approved $12.5 billion to modernize the aging national air traffic control system, according to NPR. Duffy called for further investment again after the incident, without specifying a new amount in those remarks.
The issue is noteworthy because the stoppage occurred one day after the FAA announced the rollout of an artificial intelligence tool for air traffic controllers. The controllers’ union said it had not been consulted during the design process. However, FAA Administrator Bryan Bedford said the agency saw no evidence of a connection to AI or of malicious activity. Air Space Intelligence, the maker of the SMART system, also denied that its product or its integration with the FAA was behind the disruption.
Flight cancellations continued on Saturday
The flight suspension ended, but its impact on schedules continued into Saturday. The figures vary depending on the company and the period counted: FlightAware recorded nearly 25,000 delayed flights and more than 9,000 cancellations on Friday; Cirium counted more than 8,200 cancellations on Friday night and at least 3,000 more on Saturday, according to TechCrunch. NPR cited more than 4,000 cancellations by Saturday morning, equivalent to 18% of flights departing the United States.
| Data source | Period indicated | Delays and cancellations |
|---|---|---|
| FlightAware, according to NPR | Friday | Nearly 25,000 delays and more than 9,000 cancellations |
| Cirium, according to TechCrunch | Friday night | More than 8,200 cancellations |
| Cirium, according to TechCrunch | Saturday | At least 3,000 additional cancellations |
| Cirium, according to NPR | Through Saturday morning | More than 4,000 cancellations; 18% of U.S. departures |
The differences reflect the periods and tracking services cited in each count; the published data are not a single measurement taken at the same cutoff time. Bedford said passengers would be rebooked on new flights or receive a full refund, and recommended that they contact their airlines directly. He also said he expected scheduling problems to be resolved by Sunday night.
An exceptional incident, with differing counts
TechCrunch described the incident as the third nationwide stoppage of this kind in the 21st century. NPR called it the second since the September 11, 2001 attacks and noted that the last shutdown on a similar scale occurred in 2023, following an outage of the NOTAM system, which informs pilots and airports about real-time hazards.
In that 2023 incident, the FAA determined that contracted workers had accidentally deleted essential files. The disruption prompted fears of a cyberattack at the time, but the agency later explained that the deletion was unintentional. This time, Bedford said there was no evidence of a malicious or AI-related cause and focused the public explanation on an equipment problem.
The SMART tool came up in questions because of its recent rollout, but both the FAA and Air Space Intelligence denied that it was connected to the stoppage. The investigation focused on the equipment installed during the copper-to-fiber replacement and the connections that overloaded the network; the FAA still had to establish whether the source was the hardware, the configuration, or the installation.
Sources: TechCrunch, The Verge, NPR, L3Harris® Fast. Forward.
