[3] Module 1 | The significant milestones and key events in the historical development of the aviation and air transportation industry.

4. **Boeing 247 (1933):

The Boeing 247 was the first modern airliner with features such as all-metal construction, retractable landing gear, and enclosed cockpits. It revolutionized air travel by offering increased comfort, speed, and reliability. This innovation set the standard for future passenger aircraft.

5. **Douglas DC-3 (1935):

The DC-3 was a game-changer in commercial aviation. It was the first airliner capable of turning a profit solely from passenger service. Its reliability and range made air travel more accessible, leading to the growth of the airline industry.

6. **World War II (1939-1945):

WWII had a profound impact on aviation. It saw the development of advanced military aircraft, including jet engines. After the war, these technologies were adapted for civilian use, leading to the emergence of the jet age in commercial aviation.