Boeing 737 Next Generation
The Boeing 737 Next Generation, commonly abbreviated as 737NG, or 737 Next Gen, is a twin-engine 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 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 7,136 737NG aircraft had been ordered, of which 7,120 had been delivered, with remaining orders for two -800, and 14 -800A variants. The most-ordered variant is the 737-800, with 4,991 commercial, 191 military, and 23 corporate, or a total of 5,205 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 The 737NG is superseded by the fourth generation 737 MAX, introduced in 2017.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 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 are intended to replace steel brakes and will 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 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.
The CFM56-7BE nacelle began testing in August 2009 to be used on the new 737 PIP 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 located in different places across the fuselage.
| l/n | Enhancement | Time | Launch customer | Remark |
| 1-1842 | — | — | Southwest Airlines | — |
| 1843-3569 | Short Runway Package | Mid-2006 | GOL Linhas Aéreas | Optional |
| 3570-3699 | PIP stage I | March 2011 | Ryanair | Standard |
| 3700-4301 | PIP stage II | July 2011 | China Southern Airlines | Standard |
| 4302-5554 | PIP stage III | December 2012 | United Airlines | Standard |
| 5555- | LED Light Package | Mid-2015 | Norwegian Air Shuttle | Standard |
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 degrees to 60 degrees, 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
Performance Improvement Package (PIP)
Stage II: Engine Enhancement Program
The '''CFM56-7BE engines were introduced in mid-2015 as part of the PIP for the 737 Next Generation aircraft.It provides:
- 2% improvement in fuel consumption.
- 2% reduction in carbon emission.
- 4% lower maintenance costs, depends on thrust rating bulletin.
- Improving airfoils in the HP and LP turbine.
- Reducing parts count.
- Improving engine cooling techniques.
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 located on both side of the wing roots.
- Retractable take-off light, which located on the fuselage below the ram air intakes.
- Take-off light, which located on both side of the wing roots.
- Taxi light, which located on the nose gear.
Structural problems
In 2005, three ex-Boeing employees filed a lawsuit on behalf of the U.S. government, claiming that dozens of 737NG 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 post-impact 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 should be inspected within one week, while those with over 22,600 flights should be inspected within one year. The FAA Airworthiness Directive 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.
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.