After 1920, commercial aviation began to grow as a mail delivery system. In 1925 the Kelly Airmail Act was passed by Congress to allow private air transport companies the right to bid on air delivery routes. Soon thereafter, the air mail companies began transporting passengers as a way to supplement income.
In 1926, due to the growing popularity of passenger air travel, Congress passed the first rules regulating air travel. At the time, Congress believed regulation was necessary to help the fledgling industry grow. For a while, the postmaster general was in charge of air regulation.
In 1938, the DC-3 was developed. This prop-plane was large enough to carry mail and accommodate 21 passengers. It also had three sleeping berths that could be used by passengers. Also in 1938, the federal government created the Civil Aeronautics Authority, which took over air traffic regulation from the Postmaster.
