Why Boeing’s 737s Have Flat-Bottomed Engines

One way to tell Boeing 737 family aircraft from their Airbus A320 family counterparts is that 737s have a distinctive flat-bottomed engine. But why? The Boeing 737 was designed at a time when engines were smaller and aircraft still needed to serve airports with relatively short runways and sometimes limited terminal infrastructure. Boeing also leveraged its older 727 design. Consequently, the aircraft was built with comparatively shorter landing gear.