From 1949 until 1988, Pacific Southwest Airlines (PSA) was a United States airline headquartered in San Diego, California. Founded by Kenneth Friedkin, PSA was the first large discount airline in the United States. PSA was initially operated as an intrastate airline in California, but expanded to other western states cities, as well as to several cities in Mexico, after the Airline Deregulation Act of 1978. PSA eventually merged into USAir. PSA's corporate culture was known for its humor and friendliness; the airline's slogan was "The World's Friendliest Airline," and its trademark was a smile painted on the nose of each plane while its accompanying advertising campaign employed the phase, "Catch Our Smile."