Transportation Secretary Sean Duffy said on Saturday, November 14, 2026, that a federal contractor's routine maintenance work — or a faulty router it installed — may have caused the nationwide ground stop that froze every departing flight in the United States the day before. Investigators are examining whether L3Harris workers made an error replacing old copper telecom wires with fiber optic lines at a remote FAA location, or whether the router they installed was defective.

It is the first explanation of what went wrong on Friday, November 13, when the FAA kept all departures nationwide on the ground for about four hours. More than 10,000 flights were delayed and more than 5,000 cancelled on Friday, and the disruption spilled into the weekend: 4,467 flights cancelled and 4,430 delayed by Saturday afternoon, according to FlightAware.

Key Points

• Secretary Sean Duffy said on Saturday that investigators are examining whether an error by contractor L3Harris, or a faulty router it installed, triggered the Friday nationwide ground stop.
• L3Harris workers were replacing old copper telecom wires with fiber optic lines at a remote FAA location when the system went down — work Duffy called "routine maintenance".
• The router being replaced flooded other routers in the air traffic control system with over 1,000 connection attempts every four to five seconds, disrupting communications with airplanes and radar feeds.
• Officials isolated the defective equipment within 45 minutes, but multiple facilities reported problems, so the FAA ordered the full ground stop out of caution.
• FAA Administrator Bryan Bedford confirmed zero evidence of a cyberattack, foreign interference or anything AI-related, and said no systems "went dark" or were "fully lost".

What Happened

The trouble began on Friday afternoon, when the FAA first halted departures to Chicago O'Hare and Midway over communications issues. Within hours the problem had spread across the National Airspace System, and at 3:54 p.m. Eastern Time the FAA issued the nationwide order, citing "extraordinary circumstances and for reasons of safety". The stop was lifted at about 8:15 p.m., roughly four hours later, but the damage to the weekend schedule was already done.

On Saturday, Duffy gave the first account of the trigger. L3Harris workers were carrying out planned work on the FAA's telecoms network — swapping ageing copper lines for fiber optic cable — when the system went down. The router being replaced then began flooding other routers with more than 1,000 connection attempts every four to five seconds, overwhelming the links controllers use to speak to pilots and receive radar feeds. Technicians isolated the defective equipment within 45 minutes, but several facilities had already reported problems, and with communications unreliable, the FAA stopped all departures rather than risk flying blind.

Background: An Ageing Network and a Familiar Contractor

L3Harris is no stranger to the FAA's infrastructure. The company owns the network carrying the agency's air traffic control communications and is midway through a long upgrade of what Duffy calls an "incredibly old" telecoms system. About 70 percent of the nation's lines have been replaced, but much of the network still runs on decades-old copper wire.

Hours after the stop was lifted on Friday night, President Donald Trump declared the air traffic control crisis a national emergency, and Duffy raised his funding request for a full modernisation to $50 billion, up from the $30 billion the president had sought. Friday's halt was only the third nationwide ground stop in American history, after September 11, 2001, and January 11, 2023, when a NOTAM failure grounded departures for about 90 minutes.

FAA Ground Stop Cause: The Faulty Router That Flooded the System

What stands out in Duffy's account is the volume of traffic the faulty router generated. More than 1,000 connection attempts every four to five seconds is not a gentle malfunction — it is a flood that can swamp neighbouring equipment, and that is what appears to have happened. As the bad router hammered those around it, communications with airplanes and radar feeds began to fail at more than one facility, turning a local fault into a national one.

Investigators have not yet settled the central question: whether the fault was human or hardware. "What we're working to determine was whether we had incompetence – meaning, was it user error or installator error from L3Harris — or did they install a faulty router?" Duffy said on Saturday. The distinction matters: it decides whether the failure was a mistake in how the work was done or a defective piece of equipment that should never have been fitted.

Reactions and Official Statements

Duffy was blunt about accountability. "We are going to hold people accountable," he said on Saturday, while renewing his call for $50 billion in air traffic control funding. He stressed the maintenance was routine and the failure was not caused by the FAA's new artificial intelligence systems. Homeland Security Secretary Markwayne Mullin, who announced the emergency declaration on Friday night, had already said there was no indication of a cyberattack. L3Harris did not immediately respond to requests for comment on Saturday.

Why It Matters

Friday's halt showed how much American aviation depends on a few shared systems — and Saturday's explanation showed how fragile the work to replace them can be. A single router, installed during routine maintenance, was able to flood the network and force the third nationwide ground stop in the country's history, stranding more than a million travellers in two days. The stakes are about to rise: Thanksgiving, on November 26, is the busiest travel period of the year, and the administration has promised the system will be ready.

What Happens Next

The FAA investigation continues as officials work to determine whether the cause was installer error or a defective router. Duffy's promise of accountability suggests consequences for whoever is found responsible, though he gave no timeline. Travellers should check flight status before heading to the airport, as residual delays are expected. In Washington, the $50 billion modernisation request now moves to the centre of the debate.

Frequently Asked Questions

What caused the FAA nationwide ground stop?
Secretary Sean Duffy said investigators are examining whether an error by contractor L3Harris during routine telecoms maintenance, or a faulty router it installed, triggered the stop. The router flooded other routers with over 1,000 connection attempts every four to five seconds.

Was it a cyberattack?
No. FAA Administrator Bryan Bedford confirmed zero evidence of a cyberattack, foreign interference or anything AI-related, and said no systems "went dark" or were "fully lost".

How long did the ground stop last?
About four hours: from 3:54 p.m. to about 8:15 p.m. Eastern Time on Friday, November 13, 2026.

How many flights were affected?
On Friday, over 10,000 flights were delayed and over 5,000 cancelled. By Saturday afternoon, FlightAware counted 4,467 cancellations and 4,430 delays, with up to 5,000 of 41,000 Saturday flights expected to be cancelled.

When will flights be back to normal?
FAA Administrator Bryan Bedford said full recovery is expected by Sunday, November 15, though residual delays may linger into the week.

Related coverage: FAA nationwide ground stop halts all US flights for four hours in rare outage; Trump declares air traffic control crisis a national emergency, Duffy seeks $50 billion.