In the US, it doesn’t appear that segregation laws ever applied on the planes themselves. (I'm now curious how South Africa handled the situation.) Without further research, I’m not clear if that’s because Southern states didn’t think they could regulate aviation or never got around to extending the segregation laws that applied to buses and trains. A 1963 law review article on the subject suggests that even had such laws been attempted, the concept of plenary federal power over interstate (as opposed to intrastate) commerce would have invalidated them.

When federal regulation of aviation came with the Civil Aeronautics Act of 1938, the law included a recitation (apparently copied from the Interstate Commerce Act that controlled interstate rail and bus operations) that no airline “shall . . . subject . . . any particular person . . . to any unjust discrimination or any undue or unreasonable prejudice or disadvantage in any respect whatsoever.” However, the statute offered no enforcement mechanism for this lofty goal. Apparently, the only test of this was when in 1954 Ella Fitzgerald and her tour group, traveling to Australia via PanAm on first-class tickets, were not allowed to continue from Honolulu in first-class seats. Fitzgerald sued, and eventually won the right to sue; in 1970 she told an interviewer that they received a “nice settlement.” Notably, by the time this lawsuit was brought, Brown vs. Board of Education had (only a few weeks before) swept away the “separate but equal” doctrine that might have prevented a similar recovery by a Southern plaintiff traveling on a Southern airline.

A stickier problem was the airports situated in states that required segregated waiting rooms and other facilities. However, after 1946 the federal government offered financial aid to develop and improve municipal airports, and the act required such facilities to be available “without unjust discrimination.” In 1955, the feds clarified that meant they would not finance separate facilities or spaces for separate racial groups. Still, this didn’t forbid such spaces where local laws required them, and locals were willing to pay their cost. Regulations were significantly tightened in 1960.

That year brought a cascade of events that ended airport segregation. The Supreme Court’s decision in Boynton vs. Virginia broke no new constitutional ground but spurred the Freedom Rider movement. That, in turn, prompted the Justice Department to lean on the Interstate Commerce Commission to enforce 1955 rulings made in the wake of Brown vs. Board of Education desegregating interstate bus and train facilities—including private concessions such as restaurants, even though the legal underpinnings for that remained somewhat hazy until the Civil Rights Act of 1964 finally desegregated all “public accommodations.” In early 1962, the Justice Department sent letters to airports in 14 southern states that prompted desegregation in nearly all of them, and successful lawsuits eventually desegregated three holdouts. The last “white” and “colored” signs were taken down in the Shreveport, Louisiana, airport in July 1963.

The fight to end segregated airport facilities is the subject of Anke Ortlepp’s book Jim Crow Terminals: The Desegregation of American Airports.