HC-131 Samaritan USCGConvair HC 131 Coast Guard airplane model. The Convair 240 was one of the first post World War II passenger transports. It entered airline service in June 1948 and was popular with airlines serving smaller cities where traffic did not support a larger aircraft. The Air Force had a need for a "flying classroom" for the training of navigators and radar navigator bombardiers. After evaluation, Convair was given a contract for a version of the Model 240,