US aviation shutdown: How an L3Harris-installed router disrupted thousands of flights across America

A router installed during an FAA technology upgrade may have triggered a nationwide US aviation shutdown, disrupting more than 20,000 flights. Here is what went wrong and why America's ageing air traffic control system is under scrutiny.

A routine technology upgrade may have triggered one of the biggest disruptions to US air travel in decades, after a router installed by government contractor L3Harris potentially caused a communications failure that forced the Federal Aviation Administration (FAA) to halt nearly all departing flights across the country.

The nationwide ground stop on Friday, November 13, lasted almost five hours and disrupted more than 20,000 flights through cancellations and delays.

Although the FAA lifted the restriction later that evening, the impact continued into the weekend, leaving tens of thousands of passengers stranded and airlines struggling to restore their schedules.

By Saturday evening, airlines had cancelled more than 6,150 flights and delayed over 7,300, according to FlightAware. This followed approximately 9,200 cancellations and 7,500 delays on Friday.

The FAA expected operations to return largely to normal only by late Sunday.

What makes the incident particularly significant is that investigators are looking at a seemingly small piece of networking equipment installed as part of an effort to modernise America's ageing air traffic control infrastructure.

How did one router trigger a nationwide aviation shutdown?

Transportation Secretary Sean Duffy said the problem was linked to routine maintenance being carried out by L3Harris, which is working on replacing old copper telecommunications lines with fibre-optic infrastructure.

During the upgrade, at least one new router installed at a remote facility may have triggered a chain reaction across the FAA's communications network. Officials told Reuters that problems may have involved routers installed in Arkansas and Texas.

According to Duffy, the new routers began flooding other routers with more than 1,000 connection attempts every four to five seconds. This overloaded the network and caused instability in the data being transmitted across air traffic control facilities.

The disruption affected 17 of the FAA's 22 en-route centres, which manage aircraft travelling between airports and across different regions.

The FAA said its communications systems did not completely go down and its facilities did not go dark. However, the instability meant controllers could no longer reliably exchange data through the affected routers.

The agency could not quickly establish the root cause of the problem, prompting it to take the precautionary step of grounding departing flights nationwide.

Duffy said investigators were examining whether the failure resulted from user error, an installation mistake by L3Harris or a faulty router.

L3Harris said it was taking the matter seriously and supporting the FAA's investigation. The company also said it had completed more than 70% of the planned conversion of the airspace communications network from legacy copper lines to fibre optics.

Why did the disruption continue even after flights resumed?

Lifting the ground stop did not immediately restore normal air travel.

The initial shutdown left aircraft, flight crews and passengers in the wrong places, creating a logistical problem for airlines even after the FAA declared the airspace open.

Airlines had to reposition aircraft, bring crews back into place and manage congestion at airports where planes had been waiting for departure slots or gates.

United Airlines and Delta Air Lines also announced temporary ground stops for their own flights at Chicago O'Hare and New York LaGuardia airports respectively, as they dealt with congestion and operational constraints.

The disruption affected major airlines, including American Airlines, Delta and United. Tens of thousands of passengers were left waiting at airports across the country.

FAA Administrator Bryan Bedford apologised for the disruption and said the system was stable, but warned that the recovery would take time.

US air traffic control system is ageing and expensive to maintain

The incident has renewed questions about the reliability of America's air traffic control infrastructure, much of which relies on technology that is decades old.

The routers being replaced in the latest upgrade were approximately 25 years old and were originally supposed to have been replaced in 2006, according to Duffy.

The FAA spends around $1 billion every year maintaining its old copper-wire telecommunications network while working to move to fibre-optic systems.

The problem is not simply that the technology is old. Replacing it without disrupting the existing network is proving difficult. The latest incident illustrates how an upgrade intended to make the system more reliable can itself introduce vulnerabilities if new and legacy equipment do not work together as expected.

Duffy described the episode as evidence that the existing FAA system had failed to meet the demands placed on it. He has sought $50 billion in funding to modernise air traffic control and airport infrastructure. Congress had already approved $12.5 billion for upgrades last year.

Earlier instances of flight shutdowns

This is not the first time a technology failure has grounded US flights

Friday's shutdown is the latest in a series of disruptions involving America's air traffic control network.

January 2023: The FAA issued a nationwide ground stop after a contractor accidentally deleted files in the Notice to Air Missions (NOTAM) messaging system. The disruption lasted around 90 minutes and affected approximately 11,000 flights. It was the first nationwide ground stop since the September 11, 2001 attacks.

April-May 2025: Telecommunications outages at the FAA's Philadelphia facility repeatedly disrupted flights at Newark Liberty International Airport. A brief outage in May alone resulted in 380 delays and 141 cancellations.

September 2026: Thousands of flights across the US Northeast were delayed or cancelled following two separate failures: a circuit problem at a Philadelphia air traffic facility and a fibre-optic cable accidentally severed by a construction crew in New Jersey. Around 9,500 flights were affected.

The modernisation challenge

The FAA is attempting to replace decades-old infrastructure while keeping the existing network operational. The transition involves more than replacing routers and telecommunications lines.

The agency is also working to phase out outdated floppy disks used to store weather and other critical information at more than 400 air traffic control facilities, with replacement planned by the end of 2028.

Other upgrades include replacing ageing computers and moving away from paper flight strips used by air traffic controllers to track aircraft. The transition to electronic flight strips across 49 major airports, which began in 2022, is expected to take until at least 2028.