Federal officials are investigating whether a single router installed by government contractor L3Harris triggered a massive interruption of U.S. air traffic operations that left the system effectively shut down for almost five hours and disrupted more than 20,000 flights beginning Friday.
Transportation Secretary Sean Duffy said on Saturday that the incident underscores longstanding weaknesses in the Federal Aviation Administration's telecom infrastructure. "This was an FAA system that didn’t meet the moment," Duffy said, describing the outage as a symptom of aging systems the FAA is trying to replace while keeping legacy communications running.
According to officials, routine work to migrate telecommunication lines from legacy copper wiring to fiber was underway in at least one remote location when L3Harris personnel were conducting maintenance. Duffy said Friday that L3Harris was switching lines from copper to fiber, and other officials indicated there may have been problems with routers installed in both Arkansas and Texas.
"We’re working to determine whether we had incompetence, meaning was it user error or installer error from L3Harris, or did they install a faulty router? We haven’t determined what the fault was," Duffy said. L3Harris said it took the issue seriously and was "supporting the FAA in its investigation to understand the conditions that led to the Nov. 13 ground stop of our nation’s air travel."
Officials said the newly installed routers began generating extremely high volumes of connection attempts to other routers across the FAA network - more than 1,000 connection attempts every four to five seconds - which created cascading communications instability that affected planes and radar at FAA facilities. That instability was reported across 17 of the FAA's 22 en route centers, prompting the agency to issue a nationwide ground stop because it could not immediately identify the root cause.
Bedford said the FAA had to act once it lost "the ability for those routers to communicate data." The agency has characterized the event not as a complete loss of communications but as instability in data at the centers; the centers did not go dark, the FAA said.
Those routers were originally installed about 25 years ago and had been scheduled for replacement in 2006, Duffy said. The FAA is actively working to modernize its telecom infrastructure, and L3Harris has reported completing more than 70% of the planned conversion from legacy copper wiring to fiber-optic systems.
The FAA currently spends approximately $1 billion per year maintaining its aging copper wire system even as it races to shift to fiber-based communications. To accelerate upgrades, Congress has provided $12.5 billion toward the FAA's air traffic control and telecom modernization; Duffy has requested an additional $50 billion for air traffic control and airports.
The outage is the latest in a series of high-profile failures that exposed vulnerabilities in the FAA's systems. In 2023, a contractor's accidental deletion of files led to a nationwide ground stop that lasted 90 minutes and disrupted some 11,000 flights. Other recent incidents included errant fiber cuts and a melted component that produced a strong chemical smell, each of which resulted in system failures.
Operational dependencies within the FAA remain diverse and, in some cases, decades old. The agency recently said it would replace outdated floppy disks used for weather and other critical information at more than 400 air traffic control facilities by the end of 2028. The FAA continues to rely on an older telecommunications backbone and legacy Compaq computers, with some replacement parts procured from secondary markets.
September's disruption in the densely populated Northeast, which resulted in thousands of delays and cancellations, was caused by the dual failure of a circuit at a Philadelphia air traffic facility and the accidental severing of a fiber-optic cable in New Jersey. The FAA has also been phasing in digital alternatives to long-standing paper flight strips used by controllers; the transition that began in 2022 is scheduled to reach 49 major airports by at least 2028.
Officials acknowledged the poor timing of Friday’s outage, which coincided with the start of a busy weekend travel surge. Duffy said the FAA will reevaluate scheduling of work at smaller facilities to better avoid disruptions during peak travel periods.
Investigators remain focused on pinpointing whether the problem was due to human error in installation, a defective router supplied to the FAA, or some other condition that triggered the high-volume connection attempts that led to data instability across en route centers. The FAA has not yet determined the precise root cause.
Summary
A nearly five-hour nationwide ground stop on Nov. 13 that disrupted more than 20,000 flights may have been caused by a router installed during L3Harris-led maintenance moving FAA lines from copper to fiber. The event magnifies long-standing concerns about the FAA's aging telecom infrastructure as the agency pursues modernization while maintaining legacy systems.
Key points
- Potential single-router failure - Officials say a router installed by L3Harris during copper-to-fiber migration may have triggered cascading communications instability across FAA en route centers, resulting in a near five-hour nationwide ground stop and disruptions to over 20,000 flights.
- Systemic modernization challenge - The FAA is operating and maintaining an aging telecom network while attempting a complex migration to fiber; the agency spends about $1 billion annually on the old copper system and has received $12.5 billion from Congress for upgrades, with an additional $50 billion requested by the Transportation Secretary.
- Wider operational fragility - This outage follows several recent incidents - including accidental file deletion and physical fiber cuts - that have previously hampered national air traffic operations, underscoring how localized failures can rapidly affect the broader system.
Risks and uncertainties
- Ongoing infrastructure vulnerability - Continued reliance on legacy telecom gear and older computing systems introduces the risk of further operational disruptions until modernization is completed; sectors affected include airlines, travel, and airport operations.
- Unresolved root cause - Investigations have not yet established whether the failure was due to installer error, a defective component, or another condition; the lack of a definitive cause creates uncertainty for procurement and maintenance practices within government-contracted upgrades.
- Timing and scheduling risk - Performing upgrades during high travel periods can exacerbate passenger and network impacts; adjustments to maintenance timing may be required to lower the probability of disruption to the travel sector.