The Boeing 737 is the world's most popular medium range - narrow body commercial passenger jet aircraft. With 5,851 ordered and 4,867 delivered, it is the most ordered and produced commercial passenger jet aircraft of all time. It has been continuously manufactured by Boeing Commercial Airplanes since 1967.
The 737 was born out of Boeing's need to field a competitor in the short-range, small capacity jetliner market which had been opened up by the BAC 1-11 and the Douglas DC-9. Boeing was badly behind however when the 737 program was initiated in 1964, as both of these rivals were already into their flight certification programmes. To speed up the development time, Boeing reused as much technology from the existing 707 and 727 as possible, most notably the fuselage. This gave the 737 a critical advantage over the opposition - six abreast seating compared to the 1-11 and DC-9's five abreast layout, and also made the 737 cheaper and quicker to design.
The -100 and -200 series are identifiable by their tubular engine nacelles which are integrated into the wing and project both fore and aft of it. The engines used on the Original 737 models are Pratt and Whitney JT8D turbofans. The Originals can also be identified by the smoothly curving upsweep of the tail fin - the Classics and NG models have a noticeable "kink" at the base of the fin.
The first 737 (a 100 series) took its maiden flight April 9, 1967 and entered service in February 1968 with Lufthansa, the first foreign airline to launch a new Boeing plane. The 737-200 made its maiden flight on August 8, 1967. Lufthansa was the only customer to purchase the 737-100 from new and only 30 aircraft were ever produced. The lengthened 737-200 was widely preferred and was produced until 1988. The launch customer of the 737-200 was United Airlines.
In the early 1980s the 737 had its first major facelift. The biggest change was to the CFM International CFM56 engines in place of the JT8Ds. The CFM56 was larger than the previous P&W unit, so the engine was slung underneath the wing rather than built into it. This posed a problem as the 737's limited ground clearance (a trait of the 707-derived fuselage) meant that the bottom surface of the engine nacelle had to be flattened out. At the same time, the 737 gained a partial glass cockpit from the 757 and 767. The first 737-300 entered service in 1984.
By the 1990s, the 737 had lost ground technologically to the newer Airbus A320. In 1993, Boeing initiated the 737-X or Next Generation (NG) programme.
The Next-Generation 737 encompasses the -600, -700, -800 and -900, and amounted to what was a complete redesign of the 30-year old airliner.
New wings, new avionics and revised engines were the biggest engineering changes. The 737 was given a hi-tech glass cockpit with LCD screens and digital systems heavily inspired by that used on the 777. An all new interior was designed for the Next-Generation 737, again borrowing heavily from the 777. The 737NG is an entirely new aircraft, sharing very little with previous 737s, other than fuselage frames. The parts count is down by about 33%, reducing weight and simplifying maintenance greatly. Additional changes since its introduction include a new interior and performance enhancing winglets which reduce fuel consumption and improve take-off and climb performance.
Value added enhancements, and advancements over the Airbus 320 line include the following:
Quiet Climb System (QCS) -- Automatically and consistently reduces engine thrust over noise-sensitive areas, reducing community noise and pilot workload during takeoff. Reductions depend on weight and other takeoff conditions. QCS may allow for increases in passengers and cargo as airlines can be assured of staying below airport noise limits.
Vertical Situation Display (VSD) -- Displays a side view of the airplane's flight path to the flight crew. It enhances safety by showing the airplane's current and predicted flight path relative to terrain. Additionally, it helps the pilot determine a stable and appropriate glide path during approach and landing.
Navigation Performance Scales -- Allows the airplane to navigate through a much narrower airspace envelope with greater accuracy. This can help minimize flight delays and increase airspace capacity.
Integrated Approach Navigation (IAN) -- An enhancement to an approach capability, making the pilot interface and procedures very similar to existing approaches. By allowing a common operational approach procedure, this feature minimizes pilot workload and training, reducing 18 separate approach procedures to one.
GPS Landing System (GLS) -- A highly accurate and reliable satellite-based landing system that will open additional airports and runways to regular service during most weather conditions. This system combines ground-based components with a multi-mode receiver on board the aircraft.
Head-Up Display (HUD) -- Provides "eye-level" critical flight and safety information to the pilot and can reduce takeoff and landing visibility minimums, which may mean fewer delays.
Surface Guidance System (SGS) -- An emerging technology under evaluation that improves taxi safety and airport efficiency during poor visibility and darkness, reducing the risk of runway- and taxi-related incidents.
Enhanced Vision System (EVS) -- An emerging technology under evaluation that uses thermal (infrared) imaging, which allows pilots to see objects at night and in some inclement weather, enhancing safety and potentially reducing delays.
Liquid crystal display (LCD) -- Improves readability of flight information. LCDs weigh less, require less power and generate less heat, which contributes to greater reliability and a longer service life.
In 2001, the 737 was stretched one more time to create the 737-900, which is in fact longer and carries more passengers than the 707, and steps into the capacity of the 757-200. As a result of weak demand Boeing closed the 757 line in 2004. Early in 2005, the 737 lost its distinctive "eyebrow" windows in the cockpit - once a requirement in the 1960s for added taxiway visibility but now deemed unnecessary, and a retrofit kit will be offered to remove the windows on existing aircraft.
In July 2005, Boeing announced the 737-900ER (Extended Range), formerly known as the 737-900X. The 737-900ER is the same size as the 737-900, but, with the addition of a pair of exit doors and a flat rear pressure bulkhead, will carry 26 additional passengers, raising the maximum capacity from 189 to 215 in a single-class layout. The first 737-900ER is scheduled for delivery in the first half of 2007. Lion Air will be the launch customer, with an order of 30.
Boeing has already hinted that a clean sheet replacement for the 737 will be the company's next major project after the 787, although it is still unclear if the existing 737 will receive yet one more facelift in the next 7 to 10 years.
There have been three basic generations of the 737, known as the Original, Classic and Next-Generation (NG) models.
* Original: the 737-100 and -200 (Produced from 1967 - 1988)
* Classic: the 737-300, -400, and -500 (Produced from 1983 - 2000)
* Next-Generation (or 737NG): 737-600, -700, -800, and -900 (Produced from 1997 - )
Some versions in different generations correspond to each other in size. These are:
* 737-100 — Smallest, original layout
* 737-200 — Extended version of the -100 in order to accommodate the US market
o Subvariants include:
o 737-214 (Pacific Southwest Airlines)
o 737-217 (Canadian Airlines)
o 737-219 (Air New Zealand)
o 737-221 (Pan American World Airways)
o 737-222 (United Airlines)
o 737-223 (American Airlines)
o 737-225 (Eastern Airlines)
o 737-230 (Lufthansa)
o 737-233 (Air Canada)
o 737-2B7 (USAir)
o 737-2H4 (Southwest Airlines*)
* 737-500, 737-600 — Shortened versions of the -300 and -700 respectively
* 737-300, 737-700 — The new base models, slightly stretched over the 737-200
* 737-400, 737-800 — Stretched versions mostly to accommodate charter and business airlines
* 737-900 and 900ER — Recent versions stretched even further to close a gap in Boeing's product line-up
* 737-700IGW, 737-800ERX — These variants have been awarded military contracts (see Military variants below), but the specifications have not yet been found for this encyclopedia entry.
When referring to variants of the 737, Boeing and the airlines often collapse the model (737) and the capacity designator (-300, -800, etc.) into a smaller form, either 733 or 738. The exception is the 737-700, which is abbreviated as 73G, in order to avoid confusion with the model number itself. These notations may be found in aircraft manuals or airline timetables.
Also in production is the Boeing Business Jet (BBJ and BBJ2). The BBJ is based on the 737-700 but is fitted with the stronger wings from the 737-800, while the BBJ2 is based upon the 737-800. The BBJ has increased range (by use of extra fuel tanks) over the other 737 models and is currently operated by some airlines on premium flights between North America and Europe.
The vast majority of 737s in commercial revenue service are the Classic and NG models - the Original models are quickly heading for extinction owing to poorer fuel efficiency, high noise emissions (despite the vast majority having had their JT8Ds fitted with hush kits) and escalating maintenance costs - although a large number of -200s are still in operation with "second tier" airlines and those of developing countries. No 737-100 remains in airworthy condition; however the original Boeing prototype (now owned by NASA) is now exhibited in the Museum of Flight in Seattle.
(* Southwest Airlines has the unusual distinction of being the only FAA part 61 certificated commercial airline to select a single make and model of aircraft for its entire fleet--all its planes being Boeing 737's.)
There are several versions of the 737 with special duties.
* T-43, a 737-200 - Used to train aircraft navigators for the U.S. Air Force.
* C-40 Clipper, a 737-700 - The U.S. Navy's replacement for the C-9 Skytrain II.
* Project Wedgetail, a 737-700IGW - This is an AEW&C version of the 737NG. Australia is the first customer, with Turkey, South Korea, and Italy anticipated.
* Multimission Maritime Aircraft (MMA), a 737-800ERX - On June 14, 2004, Boeing's Integrated Defense Systems division beat Lockheed Martin in the contest to replace the P-3 Orion maritime patrol aircraft. Eventual orders will probably exceed 100 from the U.S. Navy alone, with other orders from foreign navies certain to follow.
* Wingspan: between 93.0 ft and 112.6 ft (28.3 m and 34.3 m) (36 m for winglet -700, -800, -900)
o 102.5 ft (31.2 m) (600)
o 129.5 ft (39.5 m) (700, 800)
o 138.2 ft (42.1 m) (900, 900ER)
* Tail height:
o 41.3 ft (12.6 m) (600)
o 41.2 ft (12.5 m) (700, 800, 900, 900ER)
* Engines: Two high-bypass turbofan engines, rated at between 64.4 kN and 117.3 kN each
o Pratt & Whitney JT8D (100, 200)
o CFMI CFM56-3 (300, 400, 500)
o CFMI CFM56-7 (600, 700, 800, 900, 900ER)
* Maximum takeoff weight:
o 143,500 lb (65,090 kg) (600)
o 174,200 lb (79,010 kg) (700, 800, 900)
* Capacity: 85 to 189 passengers
* Cost: USD $44 million to $74 million list price in 2004 
* Autoflight, Displays, Navigation and Sensors by Honeywell
* Section 41, fuselage, and most other components produced in Wichita, Kansas. Final assembly is in Seattle-Renton, Washington.
* Cruise speed: Mach 0.74 , 420 knots (780 km/h) (Original & Classic)
* Cruise speed: Mach 0.78, 440 kt (815 km/h) (NG)
* Maximum range:
o 3,050 nautical miles (5,650 km) (600)
o 3,060 nautical miles (5,670 km) (700, 800)
o 2,745 nautical miles (5,080 km) (900)
* Hull-loss Accidents: 108 with a total of 2802 fatalities
* Other occurrences: 6 with a total of 242 fatalities
* Hijackings: 96 with a total of 325 fatalities