Intrastate airlines in the United States were air carriers operating solely within a single US state and taking other steps to minimize participation in interstate commerce, thus enabling them to escape tight Federal economic airline regulation prior to US airline deregulation in 1979. These intrastate carriers therefore amounted to a small unregulated, or less regulated, sector within what was otherwise then a tightly regulated industry. Geography alone did not determine intrastate status.

Pacific Southwest Airlines (PSA) was a low-cost US airline headquartered in San Diego, California, that operated from 1949 to 1988. It was the first substantial scheduled discount airline. PSA called itself "The World's Friendliest Airline" and painted a smile on the nose of its airplanes, the PSA Grinningbirds. The Los Angeles Times called PSA "practically the unofficial flag carrier airline of California for almost forty years."