On August 6, 2025, a problem with United Airlines’ computer system caused many flight delays and cancellations in the United States. The system, called Unimatic, gives important flight information such as aircraft weight, balance, and schedules. It stopped working for several hours in the evening. FlightAware, a flight tracking website, said more than 1,000 flights were delayed and over 200 were canceled. About 35% of United flights were delayed and 7% were canceled that day. Chicago O’Hare International Airport had 42 cancellations, most from United. The problem also affected flights in Denver, Newark, Houston, and San Francisco, and international flights to London, Frankfurt, and Munich. The cause of the problem is not known, but the system was fixed later that night.

On August 7, 2025, United said flights were starting to return to normal, but 11% were still delayed and 5% were canceled. The airline gave a travel warning that flights at many U.S. and international airports could still be delayed. The Federal Aviation Administration said it was helping United reduce the delays. United said the problem was not a cybersecurity attack and offered to pay some passenger costs, such as hotel rooms. Experts said airlines need stronger backup systems.