Sonali Tiwary
A fire alarm at United Airlines’ Network Operations Center near Chicago forced an about hour-long nationwide ground stop for all mainline flights Thursday evening, temporarily halting one of America’s largest carriers.
The alarm sounded at United’s Arlington Heights facility around 6:30 p.m. CDT on July 24, 2025, triggering an evacuation of staff to a nearby backup facility. An FAA Air Traffic Control System Command Center advisory at approximately 23:26 UTC (6:26 p.m. CDT) recorded that United had ground-stopped its mainline fleet nationwide.
“Employees have returned to our primary operations center, and the ground stop has been lifted,” United stated in an official release after operations resumed by approximately 7:30 p.m. CDT.
The temporary halt affected only mainline United flights while United Express regional service continued operating normally. At major United hubs including Chicago O’Hare (ORD), Houston (IAH), and Newark (EWR), passengers faced delays as departure boards updated with new times.
The Network Operations Center functions as the airline’s command post, monitoring all aspects of United’s global flight network. Similar to an air traffic control center but airline-specific, the NOC tracks flights, weather patterns, maintenance requirements, and crew assignments in real-time.
The impact was substantial given United’s fleet size of 1,023 aircraft and approximately 4,600 daily flights during peak periods. Industry analysts note that such system-wide ground stops can cause significant operational disruptions.
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This incident highlights the critical importance of redundant operations centers in aviation. The ability to shift operations quickly to a backup facility demonstrates the airline’s emergency preparedness protocols.
The FAA played a key role in managing the disruption through its Air Traffic Control System Command Center advisory system, which tracked the ground stop from initiation to completion.
This isn’t the first time a major U.S. carrier has faced such an operational challenge. In 2016, Delta Air Lines experienced a more severe ground stop lasting several hours due to a power surge at its Atlanta operations center.
As of July 25, United advised that flights may be temporarily delayed due to the earlier disruption. Travelers can check flight status through United’s app or website.
The disruption occurred during a week of challenging weather and transportation issues, similar to the SF Bay Coastal Flood Advisory that affected infrastructure in California. Aviation technology resilience remains crucial in modern airline operations, as shown in both Ampaire’s Electric EEL’s record-setting 12-hour flight and this brief United operations center evacuation.
The fire alarm at United’s Arlington Heights Network Operations Center caused a brief nationwide ground stop for mainline flights from approximately 6:30 p.m. to before 7:30 p.m. CDT on July 24. Staff evacuated to a nearby backup facility, and normal operations resumed within an hour. United Express regional flights were not affected during the incident.
