United Airlines experienced a widespread technology outage on the evening of August 6, 2025, leading to a nationwide ground stop of all mainline flights at major U.S. airports including Newark, San Francisco, Chicago, Denver, and Houston. The Federal Aviation Administration (FAA) acknowledged the issue and supported the airline in managing the resulting flight backlog and delays. The disruption was caused by a failure in United's Unimatic system, specifically affecting its weight and balance computer system. This outage led to the grounding of hundreds of flights, resulting in over a thousand delays and at least 200 cancellations. Approximately 35% of United's scheduled flights faced delays, and 4% were canceled on the night of the incident. United Airlines resolved the technology problem by the morning of August 7, 2025, and resumed flight operations, though residual delays continued as the airline worked to accommodate affected passengers. The company committed to covering customer expenses incurred due to the delays. The incident caused significant operational disruptions at several of United's busiest hubs and affected thousands of passengers nationwide.