The Boeing 737 Classic are narrow-body airliners produced by Boeing Commercial Airplanes, the second generation of the original Boeing 737-100/-200.Development began in 1979 and the first variant, the 737-300, first flew in February 1984 and entered service in December of that year.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.