The 737-500 was first ordered by Southwest Airlines in 1987. Southwest Airlines ordered 20 aircraft. The 737-500 flew for the first time on June 30, 1989. On February 28, 1990, Southwest Airlines got their first delivery.
After the Boeing 737 Next Generation planes were brought into service, Boeing named the 737-300/-400/-500s the 737 Classic series.
In 1991, Boeing started working on an updated group of 737s. They did this so they could have a plane to rival the Airbus A320. Boeing said that the 737 Next Generation (NG) program had begun on November 17, 1993. The -600, -700, -800, and -900 models are all part of the 737 Next Generation program. The 737 was changed so much by the 737NG program that it is almost like a new aircraft. However, some important parts of the plane were kept similar to the older 737s.
The wing was changed again. Many different changes were made. An example of one is a bigger wingspan (made bigger by ). Since the wings were made bigger, 30% more fuel could fit in the plane. CFM56-7B engines were used, which were newer, quieter and burned less fuel. The improvements to the wing, engine and fuel mean that the 737NG can travel 900 nautical miles further. This means it can travel over in total, which means that the 737NG can travel between different continents. Winglets can be added to most 737NG models. The flight deck was given modern electronics (called avionics). The main cabin was also improved.
The first NG to be built was a 737-700. It was finished on December 8, 1996. This aircraft was 2,843rd 737 built. It first flew on February 9, 1997. The prototype 737-800 was finished on June 30, 1997 and first flew on July 31, 1997. The smallest of the 737NGs, the -600, is the same size as the -500. It was the last NG to be launched (it was launched in December 1997). It first flew on January 22, 1998. The FAA certified it on August 18, 1998. A
Boeing delivered the 5,000th 737 to Southwest Airlines on February 13, 2006. The 6,000th 737 was delivered to Norwegian Air Shuttle in April 2009. The Airbus A320 family has sold more planes than the 737NG over the past ten years. However, this total includes sales for the A321 and A318. The A321 has been the rival of Boeing's 757 and the A318 has been the rival of the 717. The Next Generation series helped make sure the 737 stayed the bestselling airliner family since it first flew.
Since 2006, Boeing has been thinking about replacing the 737 with a completely new design. This was named the Boeing Y1 by people who worked at Boeing. This re-design would be launched after the Boeing 787 Dreamliner. Boeing did not decide on whether or not to go ahead with this. They said they would decide in 2011.
On July 20, 2011, Boeing said that they were working on a new 737 version, which would have the CFM International LEAP engine. American Airlines said they would order 100 of these aircraft. On August 30, 2011, Boeing said that a new 737 would definitely be launched. It was called the 737 MAX. It would also definitely have CFM International LEAP-1B engines.
The MAX 8 first carried paying passengers in May, 2017. In 2019 two MAX 8 aircraft crashed, killing all aboard and causing aviation authorities to ban commercial operation of the 737 MAX until they are fixed.
The 737's main landing gear (wheels) go into holes at the bottom of the plane. The wheels do not have a door to close over them. The tyres can be seen easily when a 737 is taking off or is flying low-down.
737s do not have fuel dump systems. A fuel dump system is a system which gets rid of any unneeded fuel if the aircraft needs to make an emergency landing while it still has a lot of fuel on board. This is useful because aircraft can only land safely at a certain weight or below. Getting rid of unneeded fuel helps to get to a safe weight for the plane to land. The first 737s were too small to need these systems. Adding a fuel dump system to the bigger 737s would make the plane much heavier. Instead, if the emergency is not very serious, 737s fly around in circles to get rid of fuel. If the emergency is serious, the 737 just needs to land at an unsafe weight. If it has to land at an unsafe weight, the plane needs to be looked at for damage. If there is no damage, the plane can be put back into service.
Engines on the 737 Classic series (300, 400, 500) and Next Generation series (600, 700, 800, 900) are not shaped like a circle like most planes. The 737 Classics had CFM56 turbofan engines. These burned much less fuel and made much less noise than the Pratt & Whitney JT8D engines which were used on the -100 and -200. However, because the 737's wings and fuselage are not very high above the ground, it was impossible to get the engines to fit on the wings. Boeing and CFM fixed this problem by putting the engines slightly ahead of the wings instead of putting them right underneath. They also moved some parts of the engines which would normally go at the bottom to the sides. This is what makes the engines non-circular.
The gearbox of the engine was moved from the bottom of the engine to the side. The gearbox makes the engine look a bit like a triangle. Since the engine is close to the ground, it is possible that they can be damaged by things lying on the ground. The CFM56-7 engine on the 737 Next Generation burns even less fuel than the engines on the 737 Classics. The Boeing 737 MAX aircraft will have CFM International LEAP-1B engines. These engines are supposed to burn 10-12% less fuel than the CFM56-7B engines on the 737 Next Generation family.
The 737's controls are very safe. If the hydraulics or both engines fail, servo tabs will be automatically used. Servo tabs are small hinges which move important parts of an aircraft. The tabs are controlled by the yoke (the thing used to steer the plane). For the 737 Next Generation, a new cockpit with LCD displays was made. These cockpits also have modern avionics (autopilot etc.).
Most 737 cockpits have "eyebrow windows". These are smaller windows which are above the main windows. There are two on each side. Eyebrow windows were used on the Boeing 707. They helped the pilot see better when the plane was turning. However, because autopilot, advanced radar etc. exist, they are no longer needed. They were removed from the 737 cockpit in 2004. However, 737s used by the military still have them installed. If the customer likes, Boeing will install eyebrow windows for them.
Winglets can be fitted to 737s which do not have them already installed. They can also be added when the aircraft is built. The winglets are about tall. They are fitted at the end of the wing and help the engines to burn less fuel because they reduce drag. They also help make less noise on takeoff. Winglets can help a plane burn up to 5% less fuel.
How the cabin looks was changed in each different type of 737 (Classic and Next Generation). The cabin design of the 737 Original was changed 737 Classic using designs from the 757. Designs from the Boeing 777 were used to design the cabin for the Next Generation 737. The newest cabin design is called the Sky Interior. It has curved walls. It also has redesigned windows. The Sky Interior has more headroom and LED mood lighting. Overhead bins which move have been installed. These bins are similar to the bins on a 777 and Boeing 787 Dreamliner. They have more space for luggage than the other designs. The Sky Interior is also designed to make the cabin less noisy by 2–4 dB. The first 737 with the Sky Interior was delivered to Flydubai in 2010. Malaysia Airlines, TUIFly and Continental Airlines have also ordered 737s with the Sky Interior.
The 737 are split into three "generations". These are Original, Classic and Next Generation. The "Original" models are the 737-100, 737-200/-200 Advanced. The "Classic" models are the 737-300, 737-400 and 737-500. The "Next Generation" models are the 737-600, 737-700/-700ER, 737-800, and 737-900/-900ER.