Paul Barkley, 59, will retire on April 30 as president and chief executive of San Diego-based PS Group, the former parent company of Pacific Southwest Airlines. Barkley will be succeeded by George M. Shortley, executive vice president of PS Group since 1985. Barkley joined the airline in 1967 as vice president of finance, and was an original officer of PS Group--formerly PSA Inc.--when the airline holding company was founded in 1973. He later became president of both companies and chairman of the airline. Barkley will remain on PS Group’s board and serve as chairman of its executive committee. PS Group completed the sale of its PSA holdings to USAir Group in 1988. The holding company now owns aircraft leasing, travel agency and fuel distribution businesses.