The Boeing 737 Classic is a series of narrow-body airliners produced by Boeing Commercial Airplanes, the second generation of the Boeing 737 series of aircraft. Development began in 1979 and the first variant, the 737-300, first flew in February 1984 and entered service that December. The stretched 737-400 first flew in February 1988 and entered service later that year. The shortest variant, the 737-500, first flew in June 1989 and entered service in 1990.

A narrow-body aircraft or single-aisle aircraft is an airliner arranged along a single aisle, permitting up to 6-abreast seating in a cabin less than 4 metres (13 ft) in width. In contrast, a wide-body aircraft is a larger airliner usually configured with multiple aisles and a fuselage diameter of more than 5 metres (16 ft), allowing at least seven-abreast seating and often more travel classes.