The Boeing Model 247 was an early United States airliner, considered the first such aircraft to fully incorporate advances such as all-metal (anodized aluminum) semi-monocoque construction, a fully cantilevered wing, wing flaps, and retractable landing gear. While the 247 and 247A had speed-ring engine cowlings and fixed-pitch propellers, the Model 247D incorporated NACA cowlings and variable pitch propellers.
Other advanced features included control-surface trim tabs, an autopilot, and deicing boots for the wings and tailplane. The Boeing 247 first flew on 8 February 1933, and entered service later that year. Subsequently, engines and airframes became larger, and four-engine designs emerged, but no significant changes to this basic formula appeared until cabin pressurization and high-altitude flight were introduced in the early 1940s with the first pressurized airliner, the Boeing 307 Stratoliner. Gould 1995, p. 14.
