In a disruptive chain of events that swept across U.S. airports on Wednesday, United Airlines was forced to ground flights nationwide due to a major system outage — throwing travel plans into disarray for thousands and igniting frustration at terminals from New Orleans to Newark.

The culprit? A failure in Unimatic, a critical technology system that United Airlines relies on for real-time flight data, including tracking times and calculating aircraft weight and balance. Though the problem was resolved late Wednesday, ripple effects extended well into Thursday, as stranded passengers tried to rebook missed connections and resume their journeys.

The scope of the disruption was massive. More than 1,000 flights were delayed, making up 35% of United’s total operations for the day. An additional 6% were outright canceled, according to FlightAware, a flight-tracking service. At United’s key hubs — Chicago O’Hare, Denver International, Newark Liberty, George Bush Intercontinental in Houston, and San Francisco International — the scene was one of mounting chaos.

At one point during the outage, the Federal Aviation Administration issued a ground stop for all United flights bound for Chicago, instructing departing planes to remain on the tarmac until further notice.

“Safety is our top priority, and we’ll work with our customers to get them to their destinations,” United said in a statement from its Chicago headquarters. The airline emphasized that the outage was not linked to cybersecurity issues, dismissing speculation of a potential hack.

But for passengers like Johan Kotze, no amount of assurances could make up for the real-world consequences. Kotze, who was scheduled to travel from New Orleans to the remote island nation of Mauritius for a long-awaited vacation, was among those caught up in the travel nightmare.

“It’s not very nice,” he said, standing amid long lines at Louis Armstrong New Orleans International Airport. Missing his initial flight likely meant missing the next few connections, not to mention the hassle of rebooking hotels, rental cars, and excursions halfway across the world.

Scenes like Kotze’s played out repeatedly on social media, as fliers turned to platforms like X (formerly Twitter) to express confusion, anger, and desperation. United’s social media team responded with repeated apologies, promising to cover hotel stays and other unexpected expenses for certain impacted travelers.

“Hey there, we apologize for the travel disruption today,” United posted to one customer. “Our teams are working to resolve the outage as quickly as possible. Thank you for your patience.”

For many, patience was in short supply.

The outage raised fresh concerns about aging infrastructure in the airline industry and the vulnerability of legacy systems like Unimatic — a platform first introduced in the 1980s, and largely phased out by other major carriers. United is one of the few airlines still heavily reliant on the system, especially for dispatch and crew communications.

Aviation experts say that while Wednesday’s failure appears to be a technical mishap rather than a malicious attack, it still highlights the fragile nature of air travel in the modern era. A single-point failure can cause cascading disruption, grounding planes, scattering crews, and turning terminals into impromptu shelters.

This isn’t the first time the industry has been rocked by IT problems. Earlier this year, another major U.S. airline faced a partial shutdown due to software glitches in its crew scheduling system. In 2023, a FAA-wide system failure briefly grounded all domestic air traffic — the first such incident since 9/11.

While the exact cause of the Unimatic failure remains under investigation, United Airlines says it’s working on system upgrades and a long-term plan to prevent a recurrence. For now, the priority is recovery: rebooking passengers, rerouting planes, and trying to rebuild traveler confidence one apology at a time.

But for the thousands of people stranded this week — many of them en route to weddings, funerals, business meetings, and long-anticipated vacations — that recovery may be too little, too late.

And for travelers like Kotze, who simply wanted to sit on a beach in the Indian Ocean, the breakdown is a painful reminder of how even the best-laid plans can be grounded in an instant.