US Airways was a major airline originally founded in Pittsburgh, Pennsylvania, as a mail delivery airline in 1939 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 enactment 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 United States' seven transcontinental legacy carriers. In 1997, it rebranded as US Airways.