The Boeing 737 Next Generation, commonly abbreviated as 737NG, or 737 Next Gen, is a twin-engined narrow-body aircraft produced by Boeing Commercial Airplanes. Launched in 1993 as the third-generation derivative of the Boeing 737, it has been produced since 1997.

The 737NG is an upgrade of the 737 Classic (–300/–400/–500) series. Compared to the 737 Classic, it has a redesigned wing with a larger area, a wider wingspan, greater fuel capacity, higher maximum takeoff weight and longer range. It has CFM International CFM56-7 series engines, a glass cockpit, and upgraded and redesigned interior configurations. The series includes four variants, the –600/–700/–800/–900, seating between 108 and 215 passengers. The 737NG's primary competition is the Airbus A320 family.

, a total of 7,159 737NG aircraft had been ordered, of which 7,123 had been delivered, with remaining orders for two -800, and 34 -800A variants. The most-ordered variant is the 737-800, with 4,991 commercial, 224 military, and 23 corporate, or a total of 5,238 aircraft. Boeing stopped assembling commercial 737NGs in 2019 and made the final deliveries in January 2020. The 737NG is superseded by the fourth-generation 737 MAX, introduced in 2017.

Development

Background When regular Boeing customer United Airlines bought the more technologically advanced Airbus A320 with fly-by-wire controls, 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.

Testing

The first NG to roll out was a 737−700, 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 737−800 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. The flight test program used 10 aircraft: 3 -600s, 4 -700s, and 3 -800s.

Enhancements In 2004, Boeing offered a Short Field Performance package in response to the needs of Gol Transportes Aéreos, which frequently operates 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 were intended to replace steel brakes and would reduce the weight of the brake package by depending on whether standard or high-capacity steel brakes were fitted. A weight reduction of on a 737-800 would result in a 0.5% reduction in fuel burn.Wilhelm, Steve. "Mindful of rivals, Boeing keeps tinkering with its 737" . Puget Sound Business Journal, August 11, 2008. Retrieved September 11, 2013. Delta Air Lines received the first Next-Gen 737 model with this brake package, a 737-700, at the end of July 2008."Boeing Next-Generation 737 Carbon Brakes Earn FAA Certification" . Boeing Press Release, August 4, 2008. Retrieved August 30, 2009.

The CFM56-7BE (Enhanced) nacelle began testing in August 2009 to be used on the new 737 PIP (Performance Improvement Package) due to enter service mid-2011. This new improvement is said to shave at least 1% off the overall drag and have some weight benefits. Overall, it is claimed to have a 2% improvement on fuel burn on longer stages.

In 2015, Boeing offered a single wing root-mounted LED light package for all 737 NG airframes, replacing the old HID light sets, which are located in different places across the fuselage. +l/nEnhancementTimeLaunch customerRemark1-1842——Southwest Airlines—1843-3569Short Runway PackageMid-2006GOL Linhas AéreasOptional3570-3699PIP stage IMarch 2011RyanairStandard3700-4301PIP stage II (engine enhancement)July 2011China Southern AirlinesStandard4302-5554PIP stage III (ram air in-outlet mod)December 2012United AirlinesStandard5555-LED Light PackageMid-2015Norwegian Air ShuttleStandard

Enhanced Short Runway Package This short-field design package is an option on the 737-600, -700, and -800 and is standard equipment for the new 737-900ER. These enhanced short-runway versions could increase pay or fuel loads when operating on runways under . Landing payloads were increased by up to 8,000 lb on the 737-800 and 737-900ER and up to 4,000 lb on the 737-600 and 737-700. Takeoff payloads were increased by up to 2,000 lb on the 737-800 and 737-900ER and up to 400 lb on the 737-600 and 737-700. The package includes: A winglet lift credit, achieved through additional winglet testing, that reduces the minimum landing-approach speeds. Takeoff performance improvements such as the use of sealed leading-edge slats on all takeoff flap positions, allowing the airplane to climb more rapidly on shorter runways. A reduced idle thrust transition delay between approach and ground-idle speeds, which improves stopping distances and increases field-length-limited landing weight Increased flight-spoiler deflection from 30 to 60°, improving aerodynamic braking on landing. A two-position tail skid at the rear of the aircraft to protect against inadvertent tailstrikes during landing, which allows higher aircraft approach attitudes and lower landing speeds

The first enhanced version, line number 1843, registered as PR-GTA, was delivered to Gol Transportes Aéreos on July 28, 2006. At that time, 12 customers had ordered the package for more than 250 airframes. Customers include: GOL, Alaska Airlines, Air Europa, Air India, Egyptair, GE Commercial Aviation Services, Hapagfly, Japan Airlines, Pegasus Airlines, Ryanair, Sky Airlines, and Turkish Airlines.

Performance Improvement Package (PIP)

Stage II: Engine Enhancement Program

The CFM56-7BE (Enhanced) engines were introduced in mid-2011 as part of the performance improvement package (PIP) for the 737NG aircraft.

It provides: A 2% improvement in fuel consumption A 2% reduction in carbon emissions A 4% lower maintenance cost, depending on thrust rating bulletin

These changes are due to: Improved airfoils in the HP and LP turbine Reduced parts count Improved engine-cooling techniques

The CFM56-7BE engine began ground testing in September 2009, and began flight testing in early 2010 in Victorville, California. The first aircraft to receive the enhancement update is line number 3700, registered as B-5596, a 737-800, which later was delivered to China Southern Airlines.

LED light package

The LED light package was introduced in 2015 as part of the development of the 737 MAX family, also applied to the 737 NG family line production shortly before the MAX's production.

The package replaced the old: Runway turn-off light, which was located on both sides of the wing roots Retractable take-off light, which was located on the fuselage below the ram air intakes Take-off light, which was located on both sides of the wing roots Taxi light, which was located on the nose gear

A single modular LED light package can be found on the wing-root where the old take-off and runway turn-off lights were. The first airframe produced with the new LED light package was a 737-800 with line number 5555, registered as EI-FHK, later delivered to Norwegian Air Shuttle.

Structural problems In 2005, three ex-Boeing employees filed a lawsuit on behalf of the U.S. government, claiming that dozens of 737NGs contained defective structural elements supplied by airframe manufacturer Ducommun, allegations denied by Boeing. The federal judge presiding the case sided with Boeing, and a subsequent court of appeal also ruled in favor of the company. A 2010 documentary by Al Jazeera alleged that in three crashes involving 737NGs—Turkish Airlines Flight 1951, American Airlines Flight 331, and AIRES Flight 8250—the fuselage broke up following impact with the ground because of the defective structural components that were the subject of the 2005 lawsuit. However, the accident investigations in all three cases did not highlight any link between postimpact structural failures and manufacturing issues.

During an inspection of a 737NG in 2019 that had 35,000 flights, fatigue cracks were found on a fuselage-to-wing attachment known as a "pickle fork", designed to last a lifetime of 90,000 flights. Boeing reported the issue to the FAA at the end of September 2019, and more planes showed similar cracking after inspection. The cracks were found in an airliner with more than 33,500 flights, when it was stripped down for conversion to freighter. Aircraft with more than 30,000 flights (15 years at 2,000 flights per year) should be inspected within one week, while those with over 22,600 flights (11 years) should be inspected within one year. The FAA Airworthiness Directive (AD) was issued on October 3, 2019.

Of the 500 first inspected aircraft, 5% () had cracks and were grounded; Boeing expected to repair the first aircraft three weeks after the issuance of the directive, serving as the template for the resulting service bulletin. Of the 810 examined aircraft over 30,000 cycles, 38 had structural cracks (%), leaving 1,911 737NGs over 22,600 cycles to be inspected within their next 1,000 cycles, i.e., nearly all of the US in-service fleet of 1,930. By early November, 1,200 aircraft were inspected, with cracks on about 60 (5%). Cracks were discovered near fasteners outside the original area in four airplanes. On November 5, Boeing recommended expanding the checks to include them, to be mandated in a November 13 FAA . Aircraft below 30,000 cycles were to be reinspected within 1,000 cycles, within 60 days above. About one-quarter of the global NG fleet of 6,300 aircraft were to be inspected.

Following the contained engine failure of the Southwest Airlines Flight 1380 on April 17, 2018, the National Transportation Safety Board recommended on November 19, 2019, to redesign and retrofit its nacelle for the 6,800 airplanes in service.

Production

Boeing was to increase 737 production from 31.5 units per month in September 2010 to 35 in January 2012 and to 38 units per month in 2013. Production rate was 42 units per month in 2014, and was planned to reach rates of 47 units per month in 2017 and 52 units per month in 2018.

In 2016, the monthly production rate was targeted to reach 57 units per month in 2019, even to the factory limit of 63 units later. A single airplane was then produced in the Boeing Renton Factory in 10 days, less than half what it was a few years before. 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°, wings are mated to the airplane in a six-hour process, along with landing gear, and the airplane is again rotated 90°. 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 and it rolls out of the factory for test flights on day 10.

Boeing stopped assembling passenger 737NGs in 2019. The last aircraft assembled was a 737-800 registered as PH-BCL to be delivered to KLM in December 2019; the last two deliveries were to China Eastern Airlines on January 5, 2020. Production of the P-8 Poseidon variant continues.

The FAA has proposed a fine of about $3.9 million for Boeing's alleged installation of the same faulty components of the 737 MAX on some 133 737 NGs.

Further developments