Boeing 247

Boeing 247

The Boeing Model 247 was an early United States airliner, considered the first such aircraft to fully incorporate advances such as all-metal (anodized aluminium) semimonocoque construction, a fully cantilevered wing and retractable landing gear. Other advanced features included control surface trim tabs, an autopilot and de-icing boots for the wings and tailplane.

"Ordered off the drawing board", the 247 first flew on February 8, 1933 and entered service later that year. Subsequently, development in airliner design saw engines and airframes becoming larger and four-engined designs emerged, but no significant changes to this basic formula appeared until cabin pressurization and high altitude cruise were introduced in 1940, with the first pressurized airliner, the Boeing 307 Stratoliner.

https://en.wikipedia.org/wiki/Boeing_247 .
http://theageofaerospace.co.uk/boeing/watch/ep1/ch4 .