AIRCRAFT
The Boeing 737 is a medium-range, narrow-body commercial jet airliner, and is the world's largest-selling jetliner with over 5,000 delivered and hundreds more on order. It has been continuously manufactured by Boeing since 1967, and at any given time, there are over 1,250 airborne worldwide. On average, one takes off or lands every five seconds.
The model is the smallest of the Boeing jetliner family and the third series of commercial jet transports to be manufactured by the Seattle company, following the 707 and the 727. Boeing announced its intention to develop a short-range, small-capacity twinjet in November 1964, by which time two other new aircraft in a similar category, the BAC One-Eleven and the Douglas DC-9, were already well advanced.
In contrast to its two competitors and to Boeings own 727, all of which had engines mounted at the rear of the fuselage, and T tails, the 737 featured a more conventional layout with the engines of the first two versions mounted directly under the wing with no intervening wing-struts (later versions have used wing-struts) and a low tailplane position. Advantages of this configuration include less structural weight per passenger carried and a significant reduction in overall fuselage length.
To speed up the development time (the BAC 1-11 and the DC-9 were already into flight certification), Boeing reused 60 percent of the structure and systems of the existing 727, most notably the fuselage cross section, which permitted six-abreast seating compared to the rival 1-11 and DC-9's five-abreast layout. The commonality also resulted in the interchangeability of passenger facilities, galley equipment, etc., for airlines using more than one Boeing jetliner type.
Named the 737 to continue the Boeing family of designations that had begun with the 707, the new type won a launch order of 22 from Lufthansa on February 19, 1965, the first time a non-U.S. airline had ordered a new American airliner that was not already in production for at least one major US operator.
While Boeing had originally planned for a 60- to 85-seat aircraft, consultation with Lufthansa resulted in a change to 100 seats.
As launched, the 737 was powered by 14,000 lb (6,350 kg) thrust Pratt & Whitney JT8D-1 engines. The first flight, by a company-owned prototype, was made on April 9, 1967, and the model was certificated on December 15, 1967, after more than 1,300 hours of flight testing by a six-airplane fleet. For the first time, certification included approval for automatic approaches in bad weather under Category II conditions, defined as 100 ft (30.5 m) ceilings and 1,200 ft (366 m) forward visibility.
The 737 is equipped with an onboard APU (auxiliary power unit), and with high-lift devices similar to those on the 727 to ensure good low-speed performance. The model entered service with Lufthansa on February 10, 1968, and that first version has the designation 737-100.
Only 30 model 737-100 were built, the last being produced in 1969 and delivered in November of that year. Interestingly, the last 737-100 delivered was actually the first 737 that Boeing produced. The aircraft had been used by Boeing as a test airplane before being delivered to NASA on July 26, 1973, for use as a test and training aircraft by the space agency. The airplane was retired from NASA in 1998 and was donated to Seattle's Museum of Flight. No 737-100s remain in service or in airworthy condition.
737-200
Production of this model hinged on a United Airlines order. The fact that United already had 727s in its fleet was an important factor in a 737/727 package that Boeing proposed. Boeing offered the airline additional 727s, with an option of returning any extra 727s when the 737s became available. In April 1965, United accepted the offer but wanted a larger version of the 737. Boeing responded by lengthening the fuselage more than 6 feet -- a 36-inch section forward of the wing and a 40-inch section aft of the wing. The stretched airplane could carry up to 124 passengers in six-abreast seating and was designated the 737-200. United ordered 40.
First flight was on August 8, 1967, and United operated the first services on April 28, 1968.
The lengthened airplane was widely preferred and was produced until 1988. Beginning with aircraft #135, a series of improvements were incorporated into the 737-200. These changes led to the introduction of the Advanced 737-200, which became the production standard. The 737-200 Advanced was also sold as the 737-200 Executive Jet and the 737-200HGW (High Gross Weight).
Boeing also provided the 737-200C (C for "Convertible"), that allowed conversion between passenger and cargo use. The 737-200QC (Quick Change) was a variation of the 737-200C, facilitating rapid conversion between roles.
The 737-200 is reaching the end of its service life owing to poor fuel efficiency, high noise emissions (despite the vast majority having had their JT8Ds fitted with hush kits) and escalating maintenance costs.
With the coming of newer versions of the 737, the -100, -200 and -200 Advanced became known as the Original models.
737 Classic series: 737-300, -400 and -500
In the early 1980s the 737 was given its first major facelift. The new 737 Classic series introduced new technology while retaining commonality with previous 737s. Fitting CFM56 engines yielded a 20% gain in fuel economy, but also posed an engineering challenge given the low ground clearance of the 737. Boeing and engine supplier CFMI solved the problem by placing the engine ahead (rather than below) the wing, and by moving engine accessories to the sides (rather than the bottom) of the engine pod, giving the 737 a distinct non-circular air intake.
The Classics also featured:
- Redesigned wing with improved aerodynamics.
- Flight deck improvements with optional EFIS (Electronic Flight Instrumentation System).
- Passenger cabin improvements similar to those on the Boeing 757.
The 737-300 was launched in 1980 by USAir and Southwest Airlines, becoming the base model of the 737 Classic series.
The 737-400 was a stretched version of the 737-300, primarily to accommodate charter airlines. Piedmont Airlines and Pace Airlines were the launch customers. The -400 was formally launched in 1986 and entered service in 1988 with Piedmont.
Third-party conversions of passenger 737 Classics into cargo aircraft are available. Kitty Hawk Cargo was the first airline to receive a 737-300F while Alaska Airlines was the first airline to convert one of their own aircraft to a 737-400F. These freighters have the ability to handle 10 pallets. No 737-500s have yet been converted.
The 737-500 was the final 737 Classic developed. It was launched in 1987 by Southwest Airlines and entered service in 1990. The -500 returned to the fuselage length of the 737-200 while incorporating the improvements of the 737 Classic series. It offered a modern and direct replacement of the 737-200, while also allowing longer and thinner routes than the 737-300.
737 Next Generation (NG) series: 737-600, -700, -800 and -900,
In 1993, Boeing launched a major overhaul of the 737 Classic series. Early in the 1990s, the modern Airbus A320 was a serious threat to Boeing's market share, as Airbus won previously loyal 737 customers like Lufthansa. After engineering studies and discussions with major 737 customers, Boeing proceeded to launch the 737 Next Generation series.
New features included:
- Improved CFM56-7 turbofan engine, 7% more fuel efficient than the CFM56-3
- New airfoil section, increased wing span, area, and chord
- Increased fuel capacity and higher MTOW
- Redesigned vertical stabilizer
- 6-screen LCD glass cockpit with modern avionics, retaining crew commonality with previous generation 737
- Passenger cabin improvements similar to those on the Boeing 777
Blended winglets are available as an option for the 737-700, 737-800 and 737-900ER as well as for Boeing Business Jets (737-700 and 737-800). They save fuel, extend range, increase payload, reduce engine maintenance costs, and improve takeoff performance.
Other options are:
- 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 narrower airspace envelope with greater accuracy. This can help minimize flight delays and increase airspace capacity.
- Integrated Approach Navigation (IAN) -- An enhancement to the 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.
The 737-600 was launched by Scandinavian Airlines System in 1995, but has suffered from weak sales, being most profitable for airlines focusing on long and thin routes. The 737-600 is the direct replacement of the 737-500 and competes with the A318.
The 737-700 was launched by Southwest Airlines in 1993 and entered service in 1998. It has the longest range of any 737 and is a direct competitor to the Airbus A319. It typically seats 132 passengers in a two-class cabin or 149 in all-economy configuration. An executive conversion is offered as the Boeing Business Jet (BBJ). This is fitted with stronger wings, the landing gear of the heavier 737-800, and has increased range through the use of extra fuel tanks.
The 737-700C is a convertible version, launched by the U.S. Navy, where the seats can be removed for the plane to carry freight. There is a large cargo door on the left side of the airplane.
Boeing launched the 737-700ER version on January 31, 2006. All Nippon Airways is the launch customer, with an entry-into-service date in early 2007. The 737-700ER is a mainline passenger version of the BBJ. It will offer a range of 5,510 nm (10,210 km), with seating for 126 passengers in a 2-class configuration. A competitor to this model would be the A319LR.
The 737-800 is a stretched version of the 737-700, and replaces the 737-400. The -800 was launched by Hapag-Lloyd Flug (now Hapagfly) in 1994 and entered service in 1998. The model seats 162 passengers in a two-class layout, or 189 in one class, and competes with the A320. For many airlines in the U.S., the 737-800 replaced aging Boeing 727-200 trijets.
An executive conversion is offered as the BBJ2 (Boeing Business Jet 2), and the 737-800ERX (Extended Range) is available as a military variant.
Boeing later introduced the 737-900, the longest variant to date. Alaska Airlines launched the 737-900 in 1997 and accepted delivery in May 2001. Because the -900 retains the same exit configuration as the -800, seating capacity is limited to 189 seats due to safety requirements. The 737-900 also retains the MTOW and fuel capacity of the -800, trading range for payload.
These shortcomings prevented the 737-900 from effectively competing with the A321.
The 737-900ER is the newest addition to the Boeing 737 line and was introduced to meet the range and passenger capacity of the discontinued 757-200. An additional pair of exit doors and a flat rear pressure bulkhead increase seating capacity to 180 passengers in a 2-class configuration or 215 passengers in a single-class layout. Additional fuel capacity and standard winglets (or optional Blended Winglets) improve its range.
The -900ER was launched on July 18, 2005, with an order for 30 airplanes from Indonesia 's Lion Air, and rolled out of the Renton, WA factory on August 8, 2006.
The Boeing 737 has also been popular as a military aircraft:
- T-43, a 737-200, used to train aircraft navigators for the U.S. Air Force. Some were modified into CT-43s which are used to transport passengers.
- C-40A Clipper, a 737-700C, the U.S. Navy's replacement for the C-9B Skytrain II. The C-40B and C-40C are used by the U.S. Air Force for transport of Generals and other senior leaders.
- Boeing 737 AEW&C, a 737-700IGW (roughly similar to the 737-700ER). This is an AEW(Airborne Early Warning )&C (Cargo) version of the airplane. Australia was the first customer (as Project Wedgetail), followed by Turkey and South Korea, with Italy anticipated.
- P-8 Poseidon, 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 may exceed 100 from the U.S. Navy. The P-8 is unique in that it has 767-400ER-style raked wingtips, instead of the blended winglets available on other 737NG variants.
- Boeing 737-2x9 Surveiller: An electronic version of a modified 737-200, used as a Maritime reconnaissance (MPA)/transport aircraft, fitted with SLAMMAR (Side-looking Multi-mission Airborne Radar.) Three aircrafts were sold to the Indonesian Air Force.
- Lockheed CATBird, a 737-300, modified with the nose of a Lockheed F-35 Lightning II, a pair of canards, and (inside) an F-35 cockpit; to be used to flight test the F-35's complete avionics suite.
On February 13, 2006, Boeing delivered the 5,000th 737. It was a 737-700 and was the 447th 737 to join Southwest Airlines' fleet, which is made up entirely of 737s.
The Future
Boeing has already hinted that a clean-sheet replacement for the 737 (internally dubbed "Y1") could follow the 787.
As of December 6, 2006, the total orders for the entire Boeing 737 range stood at 6,675, of which 5,242 had been delivered. Outstanding orders were therefore 1,433.
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