United Airlines, Inc., commonly referred to as United, is a major American airline headquartered in Chicago, Illinois. It is the world's largest airline when measured by number of destinations served, operates a comprehensive domestic and international route network, and has significant presence in the Asia-Pacific region. In the late 1920s, just prior to the use of the United Airlines name, The Boeing Company, currently one of the world's largest aircraft manufacturers, operated a predecessor airline. United was previously known as United Air Lines (UAL).