United Airlines grounds entire U.S. fleet after fire alarm at headquarters | 24 July 2025 | United Airlines was forced to issue an urgent ground stop across its entire mainline fleet on Thursday night after a fire alarm sounded at its headquarters. There were fears the decision would spark travel chaos from coast to coast just days after a similar Alaska Airlines ground stop caused hours-long delays for travelers across the United States. Passengers who were already in the air at the time of the ground stop were warned to "expect some airborne holding due to excessive demand." The ground stop has since been lifted, and a United spokesperson said: "A fire alarm sounded at our operations center, which caused employees to move to our nearby backup facility and resulted in a brief nationwide ground stop of United aircraft."