Design and development
When regular Boeing customer United Airlines bought the more technologically advanced fly-by-wire Airbus A320, this prompted Boeing to update the slower, shorter-range 737 Classic variants into the more efficient, longer New Generation variants. In 1991, Boeing initiated development of an updated series of aircraft. After working with potential customers, the 737 Next Generation (NG) program was announced on November 17, 1993. The 737NG encompasses the -600, -700, -800 and -900 variants. The NG program was the most significant upgrade of the airframe to date. The performance of the 737NG would be essentially that of a new airplane, but important commonality would be retained from previous 737 generations.
The wing was modified to increase its area by 25 percent and its span by 16 ft (4.88 m). Though a thinner cross-section was created, the total fuel capacity was increased by 30 percent. New quieter and more fuel-efficient CFM56-7B engines were used. These improvements combined to increase the 737's range by 900 nmi, permitting transcontinental service. A flight test program was performed using 10 of the new NG aircraft: 3 -600s, 4 -700s, and 3 -800s.
The passenger cabin of a 737 Next Generation aircraft improved on the previous interior of the Boeing 757-200 and the Boeing 737 Classic variants by incorporating select features from the Boeing 777 such as larger, more rounded overhead bins and curved ceiling panels. The interior of the 737 Next Generation also became the standard interior on the Boeing 757-300 and subsequently became optional on the 757-200.
In 2010, the interiors of new 737 Next Generation aircraft would include an updated interior design similar to that of the Boeing 787. Known as the Boeing Sky Interior (BSI), it introduced new pivoting overhead bins (a first for a Boeing narrow-body aircraft), new sidewalls, new passenger service units, and LED mood lighting. Boeing's newer "Space Bins" can carry 50 percent more than the pivoting bins, thus allowing a 737-800 to hold 174 carry-on bags. Boeing also offered BSI retrofits for older 737NG aircraft.
Production and testing
The first NG to roll out was a −700, on December 8, 1996. This aircraft, the 2,843rd 737 built, first flew on February 9, 1997 with pilots Mike Hewett and Ken Higgins. The prototype −800 rolled out on June 30, 1997 and first flew on July 31, 1997, piloted by Jim McRoberts and again by Hewett. The smallest of the new variants, the −600 series, is identical in size to the −500, launching in December 1997 with an initial flight occurring January 22, 1998; it was granted FAA certification on August 18, 1998.
Boeing increased 737 production from 31.5 to 35 per month in January 2012, to 38 per month in 2013, to 42 per month in 2014, and is planned to reach rates of 47 per month in 2017 and 52 per month in 2018.
The monthly production rate could reach 57 per month in 2019, even to the factory limit of 63 later. A single airplane is produced in Boeing Renton Factory in 10 days, less than half what it was only a few years ago. The empty fuselage from Spirit AeroSystems in Wichita, Kansas, enters the plant on Day 1. Electrical wiring is installed on Day 2 and hydraulic machinery on Day 3. On Day 4 the fuselage is crane-lifted and rotated 90 degrees, wings are mated to the airplane in a six-hour process, along with landing gear, and the airplane is again rotated 90 degrees. The final assembly process begins on Day 6 with the installation of airline seats, galleys, lavatories, overhead bins, etc. Engines are attached on Day 8. It rolls out of the factory for test flights on Day 10.
Ryanair 737-800 taking off
In 2004, Boeing offered a Short Field Performance package in response to the needs of Gol Transportes Aéreos, who frequently operate from restricted airports. The enhancements improve takeoff and landing performance. The optional package is available for the 737NG models and standard equipment for the 737-900ER.
In July 2008, Boeing offered Messier-Bugatti-Dowty's new carbon brakes for the Next-Gen 737s, which are intended to replace steel brakes and will reduce the weight of the brake package by 550–700 pounds (250–320 kg) depending on whether standard or high-capacity steel brakes were fitted. A weight reduction of 700 pounds (320 kg) on a 737-800 results in 0.5% reduction in fuel burn. Delta Air Lines received the first Next-Gen 737 model with this brake package, a 737-700, at the end of July 2008.
On August 21, 2006, Sky News alleged that Boeing's Next Generation 737s built from 1994 to 2002 contained defective parts. The report stated that various parts of the airframe produced by Ducommun were found to be defective by Boeing employees but that Boeing refused to take action. Boeing said that the allegations were "without merit". However, a one-year investigation by Al Jazeera's People & Power series in 2010 questions the safety of some structural parts in 737s.
As early 737NG aircraft become available on the market they are actively marketed to be converted to cargo planes via the Boeing Converted Freighter design as the operational economics are attractive due to the low operating costs and availability of certified pilots on a robust airframe.
Replacement and re-engining
Since 2006, Boeing has discussed replacing the 737 with a "clean sheet" design (internally named "Boeing Y1") that could follow the Boeing 787 Dreamliner. A decision on this replacement was postponed, and delayed into 2011.
On July 20, 2011, Boeing announced plans for a new 737 version to be powered by the CFM International LEAP-X engine, with American Airlines intending to order 100 of these aircraft. Internally, a minimum change version of the Leap-X is the probable final configuration for the proposed re-engined 737, and is expected to give a 10–12% improvement in fuel burn. Entry into service was planned for 2016 or 2017, with the new models probably being designated 737-7/-8/-9, being based on the 737-700/-800/-900ER respectively.
On August 30, 2011, Boeing confirmed the launch of the 737 new engine variant, called the 737 MAX. Its new CFM International LEAP-1B engines are expected to provide a 16% lower fuel burn than the current Airbus A320. Boeing delivered the first 737 MAX 8 to Malindo Air on May 16, 2017. The 737 MAX competes with the Airbus A320neo family.