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A short- to medium-range twinjet narrow-body airliner, originally introduced in 1968. With over 10,500 aircraft delivered and over 4500 on order, the Boeing 737 is the most popular commercial jetliner in history.

The Boeing 737 is a narrowbody twinjet airliner produced by , which first flew in 1967 and was introduced into commercial service with in February 1968. It has been continuously in production ever since then, and is the best-selling commercial jetliner in history, with the 10,000th 737 coming off the assembly line in March 2018. The 737, in all its various iterations, is also, since the last of the (the DC-9-95, marketed as the Boeing 717) left production in April 2006, Boeing's only narrowbody airliner still in production (and the only Boeing-designed narrowbody produced since production ceased in October 2004); Boeing's other three currently-produced airliners, the , , and , are all widebody (twin-aisle) aircraft. The 737's primary competition is from the family of jetliners.

The 737 has had a total of thirteen passenger variants throughout its history (plus several military or business-jet versions), falling into four families:

  • The original-series 737 (the 737-100 and 737-200), with a total of 1,125 produced from 1965 through 1988; these are easily distinguishable by their use of low- Pratt & Whitney JT8D engines, unlike all newer 737s. Due to their higher noise levels and fuel consumption compared to later models, few 737-200s remain in service, and none of the smaller 737-100.

  • The 737 Classic series (the 737-300, -400, and -500), with a total of 1,988 produced from 1984 until 2000; these are larger (except for the 737-500) than the original 737s, and feature various aerodynamic enhancements, but most of the original 737's design was, nevertheless, inherited intact (including a hitherto-unforeseen design defect in the 737's system of which could cause the to jam in the fully-deflected position). They are also the first 737s to use a high-bypass turbofan, the CFM International (GE/SNECMA)1 CFM56; due to the limited space available underneath the 737's wings, various engine components were moved from the bottom of the engine to the sides, giving the engine nacelles of all CFM56-powered 737s a highly-distinctive "hamster-pouch" shape. The new engines produce much less noise than those on the 737-100 and -200, and are more fuel-efficient; this, combined with the improved aerodynamics, gives Classic 737s a considerably greater range than the original series. However, they still burn more fuel and have a shorter range than the newer families of 737, and, as such, are being slowly replaced by 737s from these newer families (although there are still many Classic 737s in service throughout the world).

  • The 737 Next Generation (NG) series (the 737-600, -700, -800, and -900), with 7,092 produced from 1996 through 2019; these feature a larger, more efficient wing, greater fuel capacity, and a newer, more efficient variant of the CFM56 engine, all of which combine to give them greater range yet than previous 737 models. The 737 NGs are also the first 737s to use a modern "glass cockpit", with primarily electronic displays rather than mechanical gauges and dials, and the largest Next Generation 737s are a further step up in passenger capacity than the 737s that came before.
  • The 737 MAX series (the 737 MAX 7, MAX 8, MAX 200 [officially MAX 8200], and MAX 9, with another variant, the MAX 10, under development), with 387 having been produced and delivered since 2016 and over 4,500 more orders pending; these incorporate various aerodynamic tweaks (including a distinctive split-tip winglet) compared to the 737 NG series, plus an updated cabin interior, but their most visible change is the use of a new, more efficient engine, the CFM International LEAP. The LEAP is larger than the CFM56, necessitating larger and longer landing gear for the 737 MAX compared to all prior 737s (and allowing for the elimination of the hamster-pouch nacelle design), and its engine nacelles incorporate noise-reducing chevrons similar to those first seen on the . The 737 MAX series includes both the largest (737 MAX 9, soon to be displaced by the 737 MAX 10) and longest-range (737 MAX 7) 737s yet. Since March 2019, the 737 MAX series has been temporarily grounded pending a fix for a new flight-control bug (this time involving the system, used to slightly improve the aircraft's handling characteristics in certain high- flight regimes); as of January 2020, test flights are in progress, but passenger service has not yet resumed. 737 MAX production was temporarily paused starting in January 2020, with full-scale production to resume as soon as the aircraft is cleared to return to service.

The 737 may, at some point in the future, be replaced by a "New Midsize Airplane" (NMA); however, the NMA might well turn out to be yet another family of 737s (as happened with the 737 MAX series).

To learn more, see Wikipedia's articles on:

1: SNECMA was renamed to "Safran" in 2016.