At 3:36 p.m. Eastern on Friday, November 13, the FAA stopped every departing flight in the country. Roughly 3,500 planes were already in the air. Everything on the ground stayed there until 8:20 p.m. By Saturday, thousands of flights had been cancelled, sports teams were scrambling to reach weekend games, and Transportation Secretary Sean Duffy was calling it the longest of only two nationwide ground stops since 9/11.
And it happened on Friday the 13th, which meant the internet had theories before the planes had even stopped taxiing. So here they are: ten possible explanations, ranked from most to least likely, with the evidence for and against each one. Officials have since given an answer, which makes ranking easier, and also makes the bottom of the list more fun. (I used AI tools to help research and draft this post; the facts come from news reports and officials' statements published November 13 and 14, and the illustrations were made with ChatGPT.)
10 theories, one scale
Each theory gets a rating, from Confirmed down to Essentially zero, based on what officials, reporters, and the physical evidence say as of November 14.
The ranking at a glance.
1. A single router flooded the network (Confirmed)
This is the official answer. A contractor for L3Harris was replacing copper wiring with fiber at a remote FAA site. When a router was swapped in, it started flooding the other routers in the air traffic control network with about 1,000 connection attempts every four to five seconds. That traffic disrupted radar feeds and communications. The network stayed unstable for about 45 minutes, and the problem spread to 17 facilities before the FAA stopped departures nationwide.
It sounds absurd that one box in one building can ground a country. It's also the most common way big networks fail. A device misbehaves, its neighbors spend all their effort answering it, and the problem spreads faster than anyone can find the source.
One router, a thousand knocks every few seconds.
2. The routers were older than some of the controllers (Very likely, as the root cause)
The router pulled the trigger. Officials blamed the gun. FAA Administrator Bryan Bedford said the equipment involved included Cisco 600 series routers manufactured between 2001 and 2006, and the administration's line all weekend was "aging system infrastructure and legacy technology."
Older equipment isn't automatically fragile, but it tends to lack the features that stop one misbehaving device from overwhelming the rest. That's why the Trump administration used the outage to push its request for air traffic control funding to $30 billion. Reporting also noted that only about $1 billion of the $12.5 billion already approved had been spent. Old equipment is the context in which a single router can do this much damage.
Manufactured between 2001 and 2006, and still carrying radar data in 2026.
3. Someone plugged it in wrong (Likely, still open)
Here's the question officials haven't settled: was the new router defective, or did the installer configure it wrong? Both fit the facts so far. A router that floods its neighbors is often a configuration problem, but faulty hardware can do it too. Expect the official review to come down on one side. For now, it's a coin flip with the router as the coin.
4. The network had no firebreaks (Likely, as the reason it spread)
Even granting a bad router, why did one remote site take down 17 facilities? In a well-segmented network, a misbehaving device gets cut off from its neighbors before it can overwhelm them. Here, the problem spread for 45 minutes. That points to a design that lets trouble in one place reach everywhere, which is a separate failure from the router itself. Officials haven't detailed the network's layout, so this one stays at Likely.
From one router to a nationwide stop: the timeline.
5. A cyberattack (Unlikely, officials say no)
When everything stops at once, people assume someone did it on purpose. But Homeland Security Secretary Markwayne Mullin said there were no indications of a cyberattack, and Duffy said, "we don't believe this was cyber at all." The known mechanism, a router flooding the network during a hardware swap, also doesn't need an attacker to explain it. It stays on the list because investigations sometimes find surprises, but nothing so far points there.
6. Air traffic controller shortages (Unlikely, as the trigger)
The FAA's staffing shortage is real, and it has caused plenty of delays and smaller ground stops at individual airports. But staffing problems build up slowly and hit one facility at a time. They don't take down 17 facilities in under an hour. Short staffing may have made the recovery harder. It didn't cause the stop.
7. Drones (Very unlikely)
Drones have shut down airports before. London Gatwick closed for parts of three days in December 2018 after drone sightings. But drone closures are local: one airport, one airspace. Nothing in the official account mentions drones, and a drone doesn't explain radar and communications failing across 17 facilities.
8. A solar storm (Very unlikely)
Space weather can disrupt GPS and radio communications, and the sun is only a couple of years past the peak of its 11-year cycle, so it's not a crazy guess. But solar storms affect whole regions at once and don't come from a single remote building. Officials have described a wired network fault, not a radio problem, and no one has tied the stop to space weather.
9. UFOs (Essentially zero, but let's be fair)
This is the one everyone came for. It's less silly than it sounds, because unidentified objects really have closed American airspace before. In February 2023, the military shot down three unidentified objects over Alaska, Canada's Yukon, and Lake Huron within a few days, and the FAA briefly restricted airspace over parts of Montana and Lake Michigan while it was happening. The Pentagon even has an office for this: the All-domain Anomaly Resolution Office.
Here's why it still ranks ninth. Those 2023 closures were small, specific, and tied to objects tracked by radar. November 13 was the opposite: the radar feeds were the thing that failed, and the cause was found in a router, not the sky. Nothing anyone has reported points anywhere other than a building full of network equipment. If something was up there on Friday the 13th, the FAA's radar network was too busy to notice.
Theory #9: the one everyone came for.
10. Friday the 13th (Essentially zero)
Statistically, Friday the 13th is one of the most ordinary days of the year. Routers don't check the calendar. The date is the reason this outage got a thousand jokes. It is not the reason it happened. Still, if you were stuck at a gate for four hours on Friday the 13th, you're allowed to have your doubts.
Theory #10: a black cat walked across the runway. (It did not.)
What actually matters
The real story is less dramatic than a UFO and more worrying: one piece of equipment, in one remote building, during routine maintenance, stopped every departure in the United States for 4 hours and 44 minutes. Officials have ruled out an attacker. What's left is equipment that's decades old and a network where a single bad device can reach 17 facilities.
The fix is the boring kind: newer equipment, and networks built so that when one box fails, the failure stays in that box. Until then, the most likely cause of the next ground stop is the same as this one.
Which theory did you hear first on Friday? And did anyone in your group chat really commit to the UFOs?
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