Sonali Tiwary
A system outage at United Airlines disrupted travel for thousands of passengers on August 7, 2025, when a critical technology failure forced the airline to temporarily ground all its mainline flights across the United States.
The problem started at 6:12 p.m. ET when United’s decades-old internal system called Unimatic experienced technical difficulties. This legacy system houses essential flight information that feeds data to other critical systems, including those that calculate aircraft weight and balance and track flight times.
“Due to a technology issue, we are holding United mainline flights at their departure airports,” United said as the situation unfolded. The airline confirmed the outage was not related to any cybersecurity concerns that have recently affected the aviation industry.
The Federal Aviation Administration (FAA) issued ground stops at major United hubs including Chicago, Denver, Newark, Houston, and San Francisco at the airline’s request. Flights already in the air continued to their destinations, and United Express regional flights were not affected by the outage.
Transportation Secretary Sean Duffy reported being briefed by United CEO Scott Kirby on the “internal tech outage” and said FAA officials were working closely with the airline to help clear the flight backlog.
The impact on travelers was significant. About 35% of United’s flights on Wednesday were delayed, and 7% were canceled, according to flight tracking website FlightAware. Many passengers found themselves stuck on tarmacs or stranded in airports.
Angela Jeffers, whose flight from Nashville to Denver was delayed, recounted what the pilot told passengers: “We’re missing some numbers we need to take off so we can’t take off yet and don’t have a time estimate of when we’ll be able to.”
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United classified the disruption as “controllable,” meaning affected passengers were entitled to compensation under transportation regulations. The airline confirmed it was covering expenses such as hotels for impacted travelers where applicable.
The tech issue was resolved within a few hours, with systems coming back online late Wednesday night. However, the ripple effects continued into the next day, with some travelers still facing delays and cancellations on Thursday.
This incident highlights the vulnerability of airlines that rely on older technology infrastructure. The centralization of airline operations on single computer systems creates potential points of failure that can quickly cascade throughout the network.
The United outage follows a similar incident just weeks earlier when Alaska Airlines grounded its entire fleet due to an IT outage related to its weight and balance system, suggesting a potential industry-wide issue with aging technology systems.
The disruption occurred during a period of ongoing challenges at airports like Newark, where staffing shortages have already been causing significant operational problems.
