Credits to @DARZAVIATIONOFFICAL Pacific Southwest Airlines (PSA) was a regional U.S. airline headquartered in San Diego, California, that operated from 1949 to 1988. It was the first large discount airline in the United States. PSA called itself "The World's Friendliest Airline" and painted a smile on the nose of its airplanes, the PSA Grinningbirds.[1] Opinion L.A. of the Los Angeles Times called PSA "practically the unofficial flag carrier airline of California for almost forty years."[2]

The airline initially operated as an intrastate airline wholly within the state of California. This strategy which avoided the steep costs from federal regulation would later serve as the model for Southwest Airlines, doing in Texas what PSA had done in California.[3] After the Airline Deregulation Act of 1978, PSA expanded to cities in other western states, and eventually to several cities in Mexico.

PSA was purchased by USAir (later renamed US Airways) in 1986 and was fully merged into the airline on April 9, 1988. The PSA acquisition gave USAir a network on the West Coast, and at about the same time, USAir also purchased Piedmont Airlines which gave the carrier a network on the East Coast. The combined airline became one of the world's largest. US Airways was acquired by America West Airlines in 2005 in a reverse merger, and the combined airline purchased American Airlines in 2015.

American Airlines Group continues to use the PSA name and trademark for its regional airline subsidiary, PSA Airlines which operates flights on behalf of American Eagle. American Airlines also operates an Airbus A321 (previously an A319) painted in the PSA Grinningbird scheme, to pay tribute to the airline.[4]