US Airways was a major airline in the United States that operated from 1937 until 2015, when it merged with American Airlines. It was originally founded in Pittsburgh as a mail delivery airline called All American Aviation, which soon became a commercial passenger airline. In 1953, it was renamed Allegheny Airlines and operated under that name for a quarter-century. In October 1979, after the passage of the Airline Deregulation Act, Allegheny Airlines changed its name to USAir. A decade later it had acquired Piedmont Airlines and Pacific Southwest Airlines (PSA), and was one of the U.S.'s seven transcontinental legacy carriers. In 1997, it rebranded as US Airways.