United Airlines Grounds All U.S. Mainline Flights After Unimatic System Outage

United Airlines Shuts Down U.S. Flights Following Unimatic Tech Failure

Chaos gripped airports nationwide on August 7, 2025, after United Airlines was forced to ground all its mainline operations across the United States. The whole mess started with a big failure in Unimatic, United's core tech system. If you've never heard of it, Unimatic isn't just some behind-the-scenes server—it controls essential stuff like who’s balancing how much luggage, how long crews have worked, and basically every detail you need to get a giant plane safely off the ground.

Travelers hoping for a smooth summer trip woke up to find walls of flights grayed out on monitors. Over 1,000 United flights ended up delayed, accounting for a jarring 35% of the airline's entire schedule. Worse, 6% of all United flights ended up outright canceled according to FlightAware's flight tracker. Some routes were hit even harder: in San Francisco, Chicago O'Hare, Newark, Denver, and Houston, United gates all but shuttered for hours. Massive lines, tired faces, and scrambles to reach family or work quickly became the new airport normal.

FAA Steps In, Travelers Left Hanging

The Federal Aviation Administration didn't wait long. They told every United flight headed to Chicago to stay put, and similar orders followed for other key airports, sparking a domino effect at dozens of locations. Even passengers lucky enough to board before the meltdown reported long tarmac waits. Thankfully, if you were already in the air, your plans didn’t change—those flights finished their journeys as scheduled. Meanwhile, United Express—the company's regional wing—kept going like nothing happened, so a lucky few dodged the worst of it.

This outage, United emphasized, wasn't due to a cyberattack, putting to rest the first question on many frequent flyers’ minds. By evening, tech crews managed to get Unimatic back online, but by then, the disruptions had already sprawled into the next day. So, what was United’s move for those stranded or left with wrecked connections? The airline scrambled to offer travel waivers for bookings between August 6 and 14 at fourteen major airports—from Los Angeles and San Francisco all the way to Guam, Frankfurt, and London. People whose plans took the biggest hit were even offered hotel stays and reimbursed for extra expenses, but stories poured in online from travelers scrambling to rebook or find a place to sleep for the night.

• Delays hit more than a third of all United flights in the U.S.
• Thousands of travelers dealt with missed connections and surprise overnight stays.
• Many took to social media to share tales of confusion, frustration, and unexpected acts of kindness among strangers.

United publicly apologized for the mess, stressing that safety comes first and thanking passengers for hanging in. Even as the airline's systems limped back to life late that night, the impact rolled into hotels, ride-shares, and even other airlines as the aftermath of a single system failure rippled through the travel world. People who managed to reach their destinations were relieved to be off the grid—at least for one very long travel day.