The Next-Generation 737-900ER (Extended Range) is the latest member of the 737 airplane family, the world's best-selling jetliner family. Aerodynamic and structural design changes such as an additional pair of exit doors and a flat rear pressure bulkhead increase interior volume. The airplane is capable of carrying up to 180 passengers in a two-class layout and is certified for up to 220 passengers in a one-class layout.