From The Airport Wiki

Boeing's Model 247 was one of the earliest examples of a truly modern passenger airliner. The aircraft incorporated many revolutionary features such as an all-metal monocoque fuselage, autopilot, a cantilevered wing, retractable landing gear, NACA cowlings for engines, trim tabs on control surfaces, variable pitch propellers, and deicing boots for the wings and tail. Its first flight was on February 8, 1933 and entered service that same year.