FAA Ground Stop Explained: Why Every US Flight Was Grounded and What Happens Now

At 3:54 p.m. Eastern on Friday, November 13, the Federal Aviation Administration told every airport in the United States to stop letting planes take off. The order stayed in place until 8:15 p.m., four hours and 21 minutes later. It was the first nationwide ground stop since January 2023, and one of only three in the country's history. The first was on September 11, 2001.

Nobody attacked anything, as far as investigators can tell. Transportation Secretary Sean Duffy says old network equipment that connects air traffic control centers got overloaded, started producing data controllers could not trust, and was shut down on purpose. Planes already in the air landed safely.

If you are flying this weekend, the stop is over but the mess is not. This post explains what failed, why the government's own officials gave two slightly different explanations, what you are owed if your flight was cancelled, and why the same thing can happen again.

Four hours and 21 minutes, hour by hour

Duffy said the FAA first saw "instability for our radar and communications" at about 3:36 p.m. Eastern. Chicago's O'Hare and Midway airports were already under a local alert for an "equipment outage," according to NBC Chicago. Eighteen minutes later the FAA's command center sent the notice that stopped the whole country. It cited "extraordinary circumstances and for reasons of safety" and said all departing traffic should stay on the ground "until further notice."

About 3,500 planes were in the air at that moment, by Duffy's count. They kept flying and landed. Inbound international flights were handled case by case. Medical flights, including organ transport, were never halted.

By 5:31 p.m., Reagan National in Washington had no room left to park aircraft and O'Hare was close to full. JetBlue cancelled nearly everything left on its Friday schedule. When the stop was lifted, Duffy said about 400 planes were still airborne, against the 3,500 at the start.

FlightAware's running count shows how fast a pause turns into cancellations. At 6:04 p.m. it listed 1,913 cancelled US flights, according to ABC. At 7:30 p.m. the number was 4,238, with 10,079 more delayed. NBC's later tallies passed 5,300 and then 7,000. On Wednesday of the same week, the whole country had 99 cancellations.

The part that broke: routers, not radar

Air traffic controllers do not work from one building. Twenty-odd high-altitude centers and many more approach-control rooms, called TRACONs, pass aircraft to each other all day. To do that they share radar pictures, flight plans and voice lines over a private network.

That network is what failed. Duffy's description, from the White House briefing on Friday night:

"Our switches, our routers, actually got overloaded with data."

Once overloaded, he said, the equipment began giving "inconsistency in the data." Controllers had "intermittent communication and intermittent radar," meaning that at moments they could not immediately reach a pilot or see an aircraft on the screen. The FAA did not lose everything. It chose to stop departures before the picture got worse, then shut the affected system down and restarted it. The agency said it tested its systems before lifting the stop.

Duffy called the equipment "an incredibly old air traffic control system" that still runs on what he described as analog telecom. He also said the facilities already moved from analog to digital gear "did not experience these issues."

Two officials, two versions of the cause

Standing next to Duffy, Homeland Security Secretary Markwayne Mullin gave a slightly different account. He said new equipment and security patches going into the network were "overwhelming the older system," and added that "the patchwork doesn't work."

Those two statements can both be true, but they point in different directions. Duffy's version says the old gear fell over under load. Mullin's says something new was added and the old gear could not cope with it.

Reporting since then leans toward Mullin's version:

• CBS News, citing multiple sources, reported that an update to the private communications network caused a reboot, and the reboot led to the crash. CBS identified the network as the FAA Telecommunications Infrastructure, known as FTI, which is operated by the defense contractor L3Harris. L3Harris did not respond to CBS's request for comment.
• Bloomberg reported that the FBI is examining whether a software update caused the outage and does not believe a cyberattack was involved.
• The FAA itself has only called it a "temporary telecommunications outage." It has not named FTI or confirmed that an update was the trigger.

Some background on FTI helps here. The FAA awarded the contract to Harris Corp., the company that later became L3Harris, in July 2002. The network links more than 4,400 FAA facilities, according to The Register. CBS reports that a safety review commissioned by the FAA in November 2023 called the network obsolete, said it depended on an older technology called TDM, and warned that an unexpected failure could cut off facilities or an entire regional center.

That warning was written three years ago.

Was it a cyberattack, or the FAA's new AI tool?

Two theories spread quickly on Friday. Officials addressed both.

A cyberattack. Mullin said there were no "footprints" of improper access and "no indication, as of yet, that this was a nefarious act against us." He was careful not to close the door completely: "we're still looking, so we're not going to rule that out." The NSA, the Defense Department, CISA and FEMA all helped check, according to Nextgov. As of Saturday morning, no agency has reported evidence of an attack.

The AI system. The FAA has been rolling out a tool called SMART, short for Strategic Management of Airspace, Routes and Trajectories. It is built by a company called Air Space Intelligence under a 12-year contract worth $875 million, and it suggests reroutes around weather and congestion. Because the timing was close, people asked whether SMART had flooded the network.

Duffy said the tool is "completely disconnected" from the equipment that failed and that "there was no possible way SMART would have impacted what happened today." Air Space Intelligence posted that the ground stop "is not based on or a result of the SMART system." Mullin, again the more cautious of the two, said earlier in the evening that officials were looking at it and "you just can't rule out anything at this point."

So the honest status is this: no evidence of a hack, a firm denial on the AI tool from the secretary and the vendor, and a formal root cause that has not been published yet.

Flying this weekend: what the airlines owe you

The stop lasted four hours. The recovery takes days, because a ground stop leaves planes and crews in the wrong cities, and pilots and flight attendants hit legal limits on how long they can work. Duffy said the FAA would prioritize larger flights through the weekend. American warned of delays and cancellations into Saturday. JetBlue said to expect more cancellations. Southwest restarted with what it called a limited number of flights.

Here is where you stand, based on the Department of Transportation's rules:

1. If the airline cancels your flight and you decide not to travel, you get your money back. This applies whatever the cause, including an FAA outage. Refunds go to the original form of payment, within seven business days for a credit card and 20 calendar days for other methods.
2. If you accept a rebooked flight, you give up the refund. Pick one. Airlines must offer free rebooking.
3. Meals and hotels are not required. Airlines treat an air traffic control outage like weather: outside their control. NBC confirmed that no extra compensation is owed. Some airlines hand out vouchers anyway, so ask.
4. Do not cancel a nonrefundable ticket yourself. If you cancel before the airline does, you may lose the refund. Wait for the airline's cancellation or use its travel waiver.
5. Look for the waiver. American issued a travel alert that includes a refund option. Southwest said customers who rebook to another date pay no penalty.

Check your flight in the airline's app before you leave for the airport. On Friday night airlines were telling people to stay home.

Two giant outages in two days, and neither was a hack

The FAA failure landed on top of another one. Since about 1:26 p.m. Eastern on Thursday, November 12, Microsoft 365 had been broken for much of the world. Outlook email, Teams, SharePoint and Copilot were all affected.

Microsoft's explanation sounds familiar. A large number of servers "unexpectedly" became unavailable, which strained the ones still running. The company later found that a process responsible for setting up secure connections was getting overwhelmed and making servers stop responding. It paused all deployments, looked at rolling back recent configuration changes, and said it found no sign of malicious activity.

The effects were wide. According to Gizmodo and Bloomberg, Maersk warned customers about delayed email, Japanese ministries posted paper notices for reporters, some UK hospitals reported email disruption, and the Los Angeles County Sheriff's Department lost email on Thursday night.

Then on Friday afternoon, Amtrak's booking system went down for a few hours just as stranded flyers turned to trains. Amtrak blamed a system-wide update.

Mullin said plainly that there is "no connection" between the FAA outage and Microsoft's, and Microsoft said the same. Nothing in the reporting suggests otherwise. What the incidents share is the pattern: a change or a load spike hits one overloaded piece, the healthy pieces inherit its work, and they fall over too. Engineers call this a cascading failure. It needs no attacker. A routine update on a Friday is enough.

The $50 billion argument

Within an hour of reopening the airspace, Duffy turned the briefing into a funding request.

Congress approved $12.5 billion over five years in 2025 to modernize air traffic control. President Trump has asked for $30 billion more, according to NBC. Duffy wants $50 billion in an emergency bill, and Mullin said the administration wants the system fully replaced. Duffy's warning about the old equipment was blunt: "It failed, and listen, it's going to continue to fail." And about outages like Friday's: "You will have more of these."

Democrats read the same event differently. House Democratic Leader Hakeem Jeffries called it an "unprecedented breakdown" and "the latest in a series of unacceptable air travel incidents." Senator Maria Cantwell said the Commerce Committee will review the technology problems. NBC reported that senior lawmakers had not yet been briefed on Friday night.

One question neither side has answered yet matters more than the dollar figure. If an update triggered the crash, why was it pushed on a Friday afternoon, 13 days before Thanksgiving, to a network a 2023 review had already called obsolete? Money buys new routers. It does not fix change management.

What to watch next

• Saturday and Sunday. Cancellation counts on FlightAware will show how fast airlines recover. CNN reported more than 700 Saturday flights were cancelled before the day began.
• The FAA's root-cause statement. So far the agency has confirmed only a telecommunications outage. Whether it names FTI and an update will decide where the blame goes.
• L3Harris. The contractor has not commented publicly.
• Congress. Expect hearings, and a vote on emergency money that will be argued over for weeks.
• Thanksgiving. The holiday is Thursday, November 26. Duffy says the system will be "back up and operational" before the rush.

Questions travelers are asking

Is the FAA ground stop still in effect?

No. It was lifted at 8:15 p.m. Eastern on Friday, November 13. Delays and cancellations are continuing through the weekend while airlines move planes and crews back into position.

Why did the FAA ground all flights?

Network equipment that carries radar and voice data between air traffic control centers became overloaded and started giving unreliable data. The FAA stopped departures as a precaution, shut the affected system down and restarted it.

Was the FAA hacked?

Officials say there is no evidence of that. Homeland Security Secretary Markwayne Mullin said investigators found no "footprints" of improper access, though he has not formally ruled it out. Bloomberg reports the FBI does not believe a cyberattack was involved.

Was it safe to be on a plane during the outage?

Every flight in the air was accounted for and landed, according to the FAA. Pilots train for lost communications and controllers have backup procedures. Stopping departures is how the system keeps a degraded network from being asked to handle more traffic than it can.

Can I get a refund for a flight cancelled by the ground stop?

Yes, if the airline cancelled it and you choose not to travel. The cause does not matter. You are not owed meals, a hotel or extra compensation, because the outage was outside the airline's control.

Is this connected to the Microsoft outage?

No. Both the government and Microsoft say the two are unrelated. They happened a day apart and both involved overloaded infrastructure, but there is no shared system between them.

How many nationwide ground stops have there been?

Three. September 11, 2001, when all civilian air traffic was halted. January 11, 2023, when the NOTAM pilot-alert system failed for about 90 minutes after contractors accidentally deleted files. And November 13, 2026.

Sources

• CBS News: FAA lifts nationwide ground stop that disrupted thousands of flights
• NBC News: FAA orders nationwide ground stop for departing flights
• NBC News live updates: FAA lifts ground stop
• ABC News: Nationwide ground stop lifted after more than 4 hours
• Nextgov/FCW: Legacy tech issue led to FAA's nationwide ground stop
• Bloomberg: FBI said to probe whether software update caused mass FAA outage
• The Register: All US flights grounded by FAA
• Gizmodo: FAA orders nationwide ground stop for departing flights
• Flightradar24: US nationwide ground stop lifted
• US Department of Transportation: What airline passengers need to know about the automatic refund rule
• BleepingComputer: Massive Microsoft 365 outage disrupts Outlook, Teams, Copilot worldwide
• Gizmodo: Microsoft outage knocks out email for businesses, police and hospitals
• FOX 5 DC: Amtrak booking system issues amid FAA ground stop