The Boeing 737 is a twin narrow-body airliner built by Boeing. At first, Boeing was making it to be a shorter, cheaper airliner than its 707 and 727. However, the 737 has become a family of nine different models. The number of passengers it can carry ranges from 85 to 215. The 737 is the only narrow-body airliner that Boeing is making. The only types of 737 that Boeing is still making are the -700, -800 and -900ER. A version of the 737 with new engines and a new design, the 737 MAX, came into service in 2017 but was grounded in 2019 as unsafe.