Supplemental air carrier
Supplemental air carriers, until 1955 known as irregular air carriers, and until 1946 as nonscheduled air carriers or nonskeds, were a type of United States airline from 1944 to 1978, regulated by the Civil Aeronautics Board (CAB), a now-defunct federal agency that then tightly controlled almost all US commercial air transport. From 1964 onward, these airlines were just charter carriers, but until 1964 they had limited but flexible ability to offer scheduled service, making them hybrids.