Boeing 737 Next Generation (usually abbreviated to Boeing 737NG) is the designation of the −600/-700/-800/-900 models of the Boeing 737 aircraft. The series became the third generation of the 737 model and replaced the 737 Classic model (−300/-400/- 500), the production of which began in the mid-1980s. The model is a short- and medium-haul narrow-body jet aircraft. Produced by Boeing since 1996, the 737NG is sold in four passenger capacity options (usually from 110 to 210 passengers).