why is united airlines grounded

United Airlines was grounded nationwide in early August 2025 due to a significant technological issue with its weight and balance computer system, known as Unimatic. This system contains critical flight data essential for operations including calculating aircraft weight and balance and monitoring flight durations. The glitch caused the airline to issue ground stops at major hubs like Chicago, Denver, Newark, Houston, and San Francisco, leading to over 1,000 flight delays and numerous cancellations. Despite the disruption being resolved within a few hours, residual delays continued as the airline worked to restore normal operations. The Federal Aviation Administration (FAA) supported United in managing the backlog, clarifying that the issue was specific to United's operations and unrelated to the broader air traffic control system. United Airlines treated the incident as a controllable delay, covering customer expenses such as hotels and meals where applicable. The grounding caused significant passenger frustration, with many stranded on the tarmac or delayed at gates during the incident.