What broke the FAA's air traffic network? Officials blame old routers. The answers still missing.

The nationwide ground stop that halted U.S. departures for about four hours and 20 minutes on Friday began with old network equipment that got swamped, according to Transportation Secretary Sean Duffy. "Our switches, our routers actually got overloaded with data," he said. "They started to give us inconsistency in the data from those, from those routers, and because of that we shut the system down" (CBS News).

That is the administration's account of the cause. It is not a finished investigation, and it is not the only account in circulation. Officials say the outage does not appear to be a cyberattack. Reports from CBS News, The Wall Street Journal and CNN, all based on unnamed sources, describe a network update, an L3Harris-run network and a router fault. None of those reports has been confirmed. This story separates what is on the record from what is not, lays out the earlier failures that led here, and lists what officials still have to answer.

Key findings

1. Official account Officials blame an overloaded 1980s-era copper TDM network. Duffy said the problem was in the FAA's TDM, or time-division multiplexing, network, a dated, still mostly copper-wire system used to send voice and radar data, and that old switches and routers were overloaded and began producing inconsistent data (Los Angeles Times, ABC News, BBC). He said new equipment did not fail. The FAA has not released a root-cause finding and still says technicians are investigating.
2. Official account No sign of a cyberattack, but not ruled out. DHS Secretary Markwayne Mullin: "It appears that this was mechanically driven. However, we're still looking, so we're not going to rule that out" (ABC News). He also said there is no connection to Thursday's Microsoft outage (CBS Chicago).
3. Confirmed Trouble started before the stop was ordered. Duffy put the first instability at 3:36 p.m. (we read that as Eastern), 18 minutes before the 3:54 p.m. ET order (BBC, Reuters). The FAA had also halted Chicago O'Hare and Midway for an "equipment outage" shortly before (CBS News, ABC7 Chicago).
4. Unconfirmed Outside reports name a network update and L3Harris. CBS News, citing multiple sources, says an update to the private network linking air traffic control caused a reboot and crash. The WSJ says an L3Harris-overseen network that carries controllers' radio frequencies appears to be at the center. The FAA and L3Harris have not confirmed either.
5. Confirmed This is a pattern, and the money is the fight. It is at least the third major FAA telecom failure officials have described since April 2025. Congress provided $12.5 billion in 2025. The FAA said then it needed about $20 billion more. Duffy now says $50 billion, according to AP.

What officials say caused it

Duffy gave a timeline at the White House briefing (video). At 3:36 p.m., he said, "we experienced instability for our radar and our communications in our centers and our TRACONs across the country" (ABC News). TRACONs are the terminal radar facilities that handle planes near airports. Once inconsistent data began coming from the routers, the FAA ordered the nationwide stop, according to the BBC. Reuters puts that order at 3:54 p.m. ET (Reuters).

Duffy called it an "incredibly old air traffic control system" that uses analog telecom (ABC News). He also said the failure was partial. He said the system did not lose all telecom or all radar (clip of the briefing), and the BBC reported he described communications as intermittent rather than a complete blackout (BBC). That was still enough for the FAA to stop departures. He told reporters that when controllers cannot reliably communicate with or see planes, "that's a risk that we're unwilling to tolerate" (BBC).

He drew a line between old and new equipment. "Our new IP switches did not go down," he said. "It's the old hardware that went down" (CBS News video). ABC News later quoted him saying, "We use 1980s little copper lines. It's an old system that went down and went down everywhere. It got overloaded," and, "all of the new equipment that we put in, none of that went down" (ABC News). The Los Angeles Times reported that Duffy said the problem was with the TDM — time-division multiplexing — "a dated, still mostly copper-wire technology used to transmit air traffic control voice and radar data" (Los Angeles Times). The BBC reported he said the FAA was able to roll out fixes that "reduce the overloading on our switches" and "bring the networks back online" (BBC). The briefing excerpts and coverage we reviewed did not describe what those fixes were. This remains the officials' explanation, not a finished finding: the FAA's own statement still says "FAA technicians are investigating the issue" and that its information is "preliminary and subject to change" (FAA statement).

Duffy also framed the outage as a funding emergency. "This is an emergency," he told reporters. "I want Congress to give us emergency funding. This is bipartisan. This is American. I want $50 billion." He warned, "you will have more of these. You will have more of them unless the American people and the Congress tell us to build" (ABC News; also AeroTime).

Duffy said the airspace reopened at 8:15 p.m. ET: "Now does that mean every flight is going to fly right now? It's going to be slow" (CBS News). The FAA Command Center's own cancellation notice, advisory 005, took effect at 8:16 PM ET.

Mullin said no one was ever at risk. "There was never any lives at risk. There was no flights at risk" (ABC News). Pressed on whether the administration could be 100% certain it was not a cyberattack, he said, "There's nothing completely certain right now," and then, "It doesn't appear that way." The FAA's own statement, posted during the stop, said its information was "preliminary and subject to change" (FAA statement) and called it "a temporary telecommunications outage" (FAA on X).

What is reported, but not confirmed

None of the accounts in this section has been confirmed by the FAA, DHS, the White House or the companies named. They come from unnamed sources. Treat them as leads.

A network update that caused a crash. Unconfirmed "An update to the private communications network that connects America's air traffic control system caused the system to reboot, leading to a crash and a communications outage, multiple sources told CBS News. The system is operated by L3Harris, which did not immediately respond to CBS News' request for comment" (CBS News).

An L3Harris-overseen network that carries radio. Unconfirmed The Wall Street Journal, citing people briefed on the matter, reported that a telecommunications network overseen by L3Harris Technologies "appears to be at the centre" of the outage. The network handles the radio frequencies controllers use to talk to pilots, and it was not clear whether radar feeds were also affected (Times Now, citing the WSJ; Yahoo News reports the same WSJ account).

A router fault that started in Chicago. Unconfirmed CNN, citing a source in the airline industry, reported that the FAA told airlines the failures came from a problem with network routers, and that the problem is believed to have started at Chicago Midway and spread (CNN Brasil, citing CNN).

A software update, per the FBI. Unconfirmed Bloomberg, citing one person familiar with the matter, reported that the FBI does not believe the problem was a cyberattack or a criminal act, and that one line of inquiry is whether a software update caused it (Bloomberg Línea).

The Kansas City Center. Unconfirmed A pilot told a Yahoo News reporter stuck on a plane at LAX that the outage "started in Kansas City Center" and spread nationwide (Yahoo News). No official has said this.

The new AI tool. Unconfirmed The FAA put its SMART routing tool in all 22 en route centers on Nov. 10 (The Air Current). Mullin said in the afternoon that officials were "looking at" any relationship. The tool's maker, Air Space Intelligence, said the stop "is not based on or a result of the SMART system" (Los Angeles Times). Duffy's explanation points at old hardware and does not mention SMART in the coverage we reviewed.

How the accounts fit. Duffy's router explanation and CNN's router report line up. CBS's account and the WSJ's account both point at the same L3Harris-run network. They are not necessarily in conflict: an update or a fault could overload equipment. But in the coverage and clips we reviewed, neither Duffy nor Mullin addressed the L3Harris or software-update reports. L3Harris's own program page says it runs the FAA Telecommunications Infrastructure, which "securely connects more than 4,400 facilities," and claims 99.99971% network reliability (L3Harris). The reports do not name that program, and the FAA has not said whether it was involved.

The timeline: how we got here

1. Jan. 11, 2023. The FAA halts all U.S. departures for under two hours after its NOTAM system, which sends safety notices to pilots, fails. Its preliminary finding: "contract personnel unintentionally deleted files." It found no evidence of a cyberattack (FAA). That was the first nationwide stop since Sept. 11, 2001, and Friday's is the second (Yahoo News).
2. April 28, 2025. Controllers handling Newark arrivals at the Philadelphia TRACON lose radar and radio contact. A source told CNN the cause was a failure of copper wiring and that radar was out at least 90 seconds and communications for about a minute. Duffy said 30 seconds. Duffy said the backup line did not immediately take over (CNN).
3. July 2025. Congress provides $12.5 billion for air traffic control modernization in the reconciliation law, including $1.9 billion for the en route centers' facilities (Roll Call).
4. Dec. 4, 2025. The FAA names Peraton prime integrator for a "brand-new" system by the end of 2028. It says telecommunications is "one of the top priorities," that it has replaced "over one-third of copper" with fiber, and that it needs about $20 billion more beyond the $12.5 billion (FAA fact sheet).
5. Sept. 21, 2026. A circuit fails at the Philadelphia air traffic facility. When it flipped to backup, FAA Administrator Bryan Bedford said, "we discovered the backup fiber had a break." A construction crew working for NJ Transit had cut the cable. Ground stops hit Newark, Philadelphia, LaGuardia and JFK; ABC counted more than 1,000 U.S. cancellations that day (CNBC, CNN, ABC News).
6. Nov. 10, 2026. The FAA puts SMART, an AI routing tool, into all 22 en route centers (The Air Current).
7. Nov. 12, 2026. Duffy and OMB Director Russ Vought write appropriators that the earlier money was a "down-payment" and ask for $30.1 billion more, including $2 billion for "cloud computing and national airspace system telecommunications" (Roll Call). A global Microsoft outage also began Thursday.
8. Nov. 13, 3:36 PM ET. Duffy says instability began in radar and communications at the centers and TRACONs (3:36 p.m. ET) (BBC).
9. Nov. 13, shortly before 3:54 PM ET. The FAA halts O'Hare and Midway for an "equipment outage" (CBS News, ABC7 Chicago).
10. Nov. 13, 3:54 PM ET. The FAA orders the nationwide ground stop (3:54 p.m. ET) (Reuters).
11. Nov. 13, 8:15 PM ET. Duffy says the airspace reopened at 8:15 p.m. ET. Advisory 005, effective 8:16 PM ET, cancels the stop (BBC, FAA).
12. Nov. 13, evening. At the White House, Duffy calls the outage an "emergency," asks Congress for $50 billion, and blames an overloaded 1980s-era copper TDM network, saying new equipment did not fail. Mullin says officials have seen zero evidence of a cyberattack and that the investigation continues (ABC News, Los Angeles Times, DHS).

Duffy's Friday account fits a pattern he and the FAA have described before: an aging telecom backbone, with at least one failure in September where the backup also failed. It does not yet show why the failure on Friday spread to the whole country, which is the question the 2025 and September outages also raise.

The money

The FAA's December 2025 fact sheet said Congress's $12.5 billion was a "down payment" and that it needed an additional $20 billion (FAA). On Thursday, Duffy and Vought asked for $30.1 billion more (Roll Call). At Friday's briefing, Duffy raised that figure to $50 billion. ABC News quoted him: "This is an emergency. I want Congress to give us emergency funding. This is bipartisan. This is American. I want $50 billion" (ABC News). AP and the BBC reported the same figure (WISN, an AP report, BBC). AeroTime noted that Duffy and OMB Director Russ Vought had asked lawmakers for $30.1 billion that morning, and that Duffy did not explain how the $50 billion figure related to that request (AeroTime).

Duffy framed the choice for Congress: "do you want your Congress to fund this?" and "Let's not do a patchwork fix" (clip of the briefing). Senate Commerce Committee Republicans called the stop a "rare but major disruption," pointed to the $1.9 billion for en route center upgrades in the 2025 law, and noted that President Lyndon B. Johnson was in office the last time a new en route center was built (Roll Call).

Who is asking questions

Sen. Tammy Duckworth, the ranking Democrat on the Senate aviation subcommittee, said: "The safety of our skies is built on redundancies. Whatever led to the nationwide ground stop will warrant a thorough and complete investigation." She said she will demand answers from the FAA (X).

Sen. Maria Cantwell, the Commerce Committee's top Democrat, said: "Technology issues related to how planes communicate through primary frequencies, backup frequencies, and other issues will be something the Commerce Committee will be reviewing." (X). Roll Call notes she is set to take the gavel in January when Democrats assume the Senate majority (Roll Call). Rep. Ted Lieu told the Los Angeles Times there should be hearings and that the FAA needs systems without a single point of failure (Los Angeles Times). No hearing date has been announced.

The controllers' union, NATCA, said controllers "are on the job" during the stop (BBC). The Air Line Pilots Association said it was in contact with the FAA and NATCA (X). We did not find an on-the-record statement from NATCA or the air traffic supervisors' union PASS about the cause.

What it cost passengers

ABC News counted nearly 5,000 cancellations on Friday (ABC News). Later Friday, Reuters, citing FlightRadar24, reported more than 6,600 cancellations and 8,600 delays, with another 1,500 flights already canceled for Sunday (Reuters). At Chicago alone, airlines canceled 675 flights at O'Hare and 37 at Midway (CBS Chicago). FlightAware showed nearly 800 cancellations already for Saturday (ABC7). JetBlue warned of more Saturday cancellations, AeroTime reported, and its travel-alerts page, updated at 10 PM ET, says it plans to resume flights Saturday morning (AeroTime, JetBlue). The disruption reached beyond the U.S.: the stop forced cancellations of flights from Canada and Europe, Reuters reported. Duffy said a return to normal will take time (ABC News); aviation analyst Robert Mann told Reuters that a stop running into the evening would likely take the weekend to sort out.

If an airline cancels your flight and you decline the rebooking or a voucher, DOT rules entitle you to a refund even on a nonrefundable ticket (14 CFR 260.6). Tarmac-delay rules require food and water within two hours and a chance to deplane by three hours on domestic flights (14 CFR 259.4). More in our first story.

Open questions

1. What exactly failed? Duffy has now named the FAA's TDM, or time-division multiplexing, network and 1980s-era copper lines. Which switches and routers, who owns and operates them (the FAA or the L3Harris-run network), and what flooded them with data still have not been spelled out. The FAA has not published a root-cause finding and still says technicians are investigating.
2. Was there an update or change? CBS's sources say a network update triggered a reboot and crash. The FAA and L3Harris have not said whether any change was made before the failure.
3. Why did one fault become a national shutdown? The Chicago stops preceded the national order by minutes. Why did redundancy not contain it, as Duckworth and Cantwell are asking about primary and backup systems?
4. What happened in the 18 minutes? Duffy says instability began at 3:36 p.m. ET and the stop came at 3:54. What did the FAA know, and what did it try, in between?
5. What fixed it? Duffy said fixes "reduce the overloading on our switches" and restored the networks. Which fixes, and do they hold if the load returns?
6. Was it connected to SMART? Mullin said officials were looking at it. The vendor denies it. AeroTime later reported Duffy said the SMART tool played no role. Has the FAA formally ruled it out in a finding?
7. Who investigates, and when do we see the result? Democrats are demanding answers, and Rep. Ted Lieu has called for congressional hearings, but no hearing date, inspector general review or FAA root-cause report had been announced in the coverage we reviewed. After the 2023 NOTAM outage, the FAA traced the failure to a damaged database file the same day and announced its preliminary finding about deleted files eight days later.
8. Is the funding ask the right fix? The ask grew from about $20 billion (FAA, December 2025) to $30.1 billion (Thursday) to $50 billion (Friday). What is the cost breakdown, and which of it addresses telecom backups?
9. Why don't the counts match? Duffy said "over 3,500" planes were airborne; Reuters, citing Flightradar24, said 4,042 were headed to U.S. airports; CBS, also citing Flightradar24, said about 3,100. Different definitions may explain it, but officials have not said.

What we could not verify

• A formal root-cause finding. Duffy's TDM explanation is on the record, but no document from the FAA, DOT or L3Harris describes a finished technical finding. The FAA still says technicians are investigating.
• L3Harris's role. Reported by CBS and the WSJ; no confirmation or denial that we could find.
• The time zone Duffy used for "3:36 p.m." ABC and the BBC do not label it. We read it as Eastern because the briefing was in Washington and the stop was ordered at 3:54 p.m. ET.
• Whether the Chicago equipment outages and the national failure share a cause.
• Any NATCA or PASS statement on the cause.

How we reported this

Delay Wire staff read the FAA's advisories and statements, the White House, DHS and congressional posts on X, and reporting from ABC News, CBS News, the BBC, Reuters, AP (through WISN), Roll Call, the Los Angeles Times, AeroTime, CNN and The Air Current. We checked Duffy's quotes against two outlets' written accounts and against audio of the briefing clips posted on X. Quotes are verbatim from the sources linked beside them. Reports based on unnamed sources are labeled Unconfirmed. We have not contacted L3Harris, the FAA or DOT directly. If you have information or a correction, use the comments on the live tracker.