UAL Corporation (UAL) is a holding company whose principal subsidiary is United Air Lines, Inc. (United). Most of UAL's revenue during the year ended December 31, 2008, was from United's airline operations. United transports people and cargo through its Mainline operations, which utilize full-sized jet aircraft exceeding 70 seats in size, and its regional operations, which utilize smaller aircraft not exceeding 70 seats in size that are operated under contract by United Express carriers. United Airlines operates more than 3,300 flights a day on United, United Express and Ted to more than 200 United States domestic and international destinations from its hubs in Los Angeles, San Francisco, Denver, Chicago and Washington, D.C. The Company operates in two business segments: Mainline and United Express.