Travelers passing through Chicago and other United Airlines hubs woke up Thursday to lingering disruptions after a software outage triggered more than 1,000 flight delays across the carrier’s global network. While United declared the glitch resolved late Wednesday, the cascade of scheduling snarls continued into the morning as the airline worked to reposition aircraft, re-crew flights, and accommodate stranded passengers in Chicago, Denver, Newark, Houston, and San Francisco.
What went wrong with United’s Unimatic system?
United blamed the operational meltdown on Unimatic, an internal platform that stores real-time flight information and feeds weight-and-balance data as well as departure and arrival times to a constellation of other systems. The carrier has not said what caused the failure, only that it was not linked to cybersecurity concerns. The outage lasted “several hours,” the airline noted in an emailed statement. Because Unimatic touches nearly every corner of the operation, the knock-on effects were swift. FlightAware, a website that tracks airline performance, logged delays on about 35% of United’s worldwide schedule and cancellations on 7% of its flights on Wednesday. By late Thursday morning in Chicago, the same site showed delays on 9% of the carrier’s flights and cancellations on 5%.
Chicago bears the brunt, but hubs coast-to-coast feel pain.
Nowhere were the numbers more visible than at Chicago O’Hare International Airport, United’s largest base. FlightAware tallied 42 cancellations there by midday Thursday, 41 belonging to United. The Federal Aviation Administration went as far as to ground all United-bound flights headed for Chicago on Wednesday evening while technicians worked to restore the data feed. Flights into other mainline hubs—Denver International, Newark Liberty, George Bush Intercontinental in Houston, and San Francisco International—also saw ground stops or lengthy taxi-out holds. United’s travel-alert page, updated overnight, warned customers that trips to or from Denver, Newark, Washington, Houston, New York, Los Angeles, Orlando, Chicago, San Francisco, Honolulu, and Guam could still see schedule changes. European gateways at London Heathrow, Frankfurt, and Munich remained on the watch list as well.
Real-world ripple: passengers stuck on the tarmac
Inbound aircraft often had nowhere to park once they landed, leading to extended waits on taxiways and remote pads. “The first hour, people were already standing up and just walking around the cabin because there was nothing to do,” passenger Benjamin Fuentes said as he recounted his Boston-to-Houston trip to KTRK-TV. After learning the system was down nationwide, Fuentes finally reached a gate—but only after an additional 45-minute crawl.
United pledges hotel vouchers and expense coverage
United classified the outage as a “controllable delay,” meaning the airline will shoulder the cost of hotel rooms and other reasonable expenses when travelers miss connections or face overnight disruptions. “Safety is our top priority, and we’ll work with our customers to get them to their destinations,” the airline said in a prepared statement. The company also took to social media to answer individual complaints. “Hey there, we apologize for the travel disruption today,” the airline wrote on X in response to one flier. “Our teams are working to resolve the outage as quickly as possible.”
Regulators monitor recovery effort
The FAA said it was aware of the technical issue and remained in “close contact” with United while offering assistance to unwind the backlog. “We’ve offered full support to help address their flight backlog,” the agency said in a statement.
Tips for Travelers: Navigating the aftermath of the United Airlines delays
- Check flight status frequently. Even flights showing on time can flip to delayed as aircraft repositioning continues.
- Hold on to receipts for meals, hotels, and ground transportation—United has confirmed it will reimburse reasonable expenses tied to the outage.
- Use the airline’s app or website to self-rebook; call centers are experiencing high volume and longer wait times.
- If connecting through Chicago, consider longer layovers or alternative routings until on-time performance normalizes.
- International passengers should verify onward connections; European hubs in London, Frankfurt, and Munich are still seeing sporadic delays.
Why tech outages sting airlines—and their passengers
Airlines run on tightly choreographed data streams that synchronize crew schedules, aircraft assignments, and passenger manifests. When one essential system, such as Unimatic, freezes, the domino effect can idle planes in the wrong cities, trigger mandatory crew rest breaks, and erase buffer time built into complex daily schedules. Even after the root cause is addressed, staffing and gate availability often lag, keeping ripple delays alive for another 24 to 48 hours.
When will operations return to normal?
United has not published a definitive timeline. Historically, major carriers require roughly one operational day for every hour of large-scale disruption to smooth out the remaining bumps. Given Wednesday’s multi-hour outage, travelers should plan for pockets of irregular operations into the weekend, particularly on flights touching the airline’s largest connecting hubs in Chicago and Newark.
Bottom line for JetsetterGuide readers
The Unimatic outage shows how a single system hiccup can paralyze a global airline overnight. If you’re flying United in the next few days, monitor your itinerary like a hawk, keep receipts, and know that the carrier is on the hook for reasonable out-of-pocket costs. Patience helps, but a backup plan—and maybe a downloaded Netflix season—doesn’t hurt either.
