The Boeing 737 is probably one of the most talked about aircraft of the last few months. While the latest MAX series has grabbed all the headlines, the 737 story can trace its roots back to the mid 1960’s.
In the Beginning
The original plan for the company was to have the three engined 727 to be the workhorse of the short haul fleet and the new 737 to supplement it. Initially the 737 was designed to be a lot like the Douglas DC9, with 5 abreast seating, rear mounted engines and a T-tail. However as the design process went on, the engines were moved under the wing in order to widen the fuselage and therefore enable 6 abreast seating. This also meant the whole structure was lightened resulting in increased fuel efficiency. To further keep costs down, Boeing carried over many of the parts and systems from their 727 model.
Although the 737 is one of the most successful aircraft types today, this wasn’t always the case. The initial 737 variant only sold 30 units, mostly to the German airline Lufthansa. It was only when US airline United wanted a larger aircraft that the type became more popular. As such, the initial variant destined for Lufthansa was dubbed the 737-100, where as the larger version (stretched by almost a metre) was given the 737-200 designation. Both the -100 and -200 were developed alongside each other, with the -100 rolling out in December 1966 before making its first flight in April 1967. It gained certification from the FAA in early December 1967, before the first aircraft was delivered to Lufthansa a few weeks later. The airline put the new aircraft into service in February 1968. The -200 variant was a few weeks behind the -100, with certification coming just a few days before Christmas in 1967 and United Airlines putting the type into service at the end of April 1968.
Despite low sales through the late 1960’s, Boeing continued to develop the type, introducing improved thrust reversers, wing fairings, flaps, more powerful engines, and an increase in fuel capacity. All of these enhancements led to Boeing selling the aircraft as the -200Advanced, which would be the only 737 option from 1971 after the -100 went out of production in 1969. Despite the improvements, sales were still far less than anticipated due to airlines preferring the tried and tested Boeing 727, Douglas DC9 and Fokker F27. Boeing considered calling time on the project after just 22 aircraft were delivered in 1972. Luckily for Boeing, the US Air Force placed an order for 19 modified -200 models, which would be designated the T43. Funds were also able to be allocated to the 737 project after the cancelled Boeing Supersonic Transport project, and cutting back on the 747 Jumbo production. Sales would remain somewhat low until the US Airline Deregulation Act in 1978 meant there was increased demand for the type.
By the end of the 1970’s, it became apparent to Boeing that their previously popular 727 wouldn’t be the best option for the future, due to its three engines. So the company set about further developing their 737 product instead. The most noticeable improvement to the new type was the new CFM engines – although this caused a few issues. As the original 737 sat very low to the ground in order to ease access to the engines, this meant fitting larger engines would require a rethink. This included reducing the fan size of the new engine, moving it almost completely forward of the wing and moving certain components to the side of the engine, resulting in a unique almost triangular flat bottomed shape. Further improvements consisted of upgraded wings, an upgraded tailfin, a 2.8 metre stretch of the fuselage, a cabin based on the 757 that was in development at the time and an upgraded electronic flight desk. This new variant was given the -300 designation and the project was launched at the 1980 Farnborough Air Show. Initial orders for the type came in 1981, with both Southwest and US Air ordering 10 aircraft each. The first flight of the -300 came in 1984, entering into commercial service by the end of the year.
The -300 series was a far more popular aircraft than its predecessor, receiving over 250 orders in 1985 alone, so the same year Boeing launched a stretched version to fill the gap between the -300 and the companies recently released 757-200. The -400 variant was 10 feet longer than the -300 enabling it to carry around 35 more passengers depending on customer specification. The variants production was confirmed in mid 1986 when Piedmont Airlines ordered 25 aircraft, with an option for 30 more. The -400 first flew in February 1988 and entered commercial service in September of the same year. The final -400 variant rolled off the production line in the year 2000 after 12 years in production. The final variant of what’s now known as the 737 “Classic” was the -500. By 1987, the -200 was needing to be replaced with a more modern counterpart, so Boeing launched almost a direct replacement for the older variant, with only a minor fuselage stretch but the updates from the previous -300 series. The first -500 was delivered to US based Southwest Airlines in February 1990.
By the late 1980’s, European competitor Airbus had launched the ultra modern A320 series so Boeing had to act reasonably fast so as not to lose the market share. By the end of 1993, the company was ready to announce the “Next Generation” of the 737, which was by far the most significant upgrade of the type. Although by this time, the company had already lost a couple of major customers in Lufthansa and United Airlines, who had placed large orders for their European counterparts.
The 737NG series, comprising of the -600, -700, -800 and -900 variants was once again, a major update of the 1960’s design. The latest iteration featured larger, redesigned wings, updated and more fuel efficient CFM engines, a higher cruising speed, a digital flight deck and a redesigned cabin and interior. They also feature a major range increase over previous variants in order to bring the series into line with the Airbus A320 series.
The first of this new series, a -700 was rolled out in December 1996 with the first flight taking place in February 1997. The most popular variant, the -800 made its first flight in July of the same year with the smallest and arguably the least popular variant, with just 69 produced, the -600 made its first flight in January 1998.
The launch customer of the NG series was Southwest Airlines, who now operate a fleet of 754 Boeing 737’s. Since then, a total of 6996 of the series has been produced as of January 2019 making this variant by far the most popular of the 737. The basic plan was a lot like the previous generation of the 737 – the -600 was to replace the -500, which in turn replaced the previous -200 and is a competitor for the Airbus A318. The larger -800 competed with the Airbus A320 and not only served as a replacement for the -400, but also replaced the aging Boeing 727 for many airlines in the US. The -700 was an update of the popular -300 series and a direct competitor for the Airbus A319.
The final basic variant of the 737NG series was the -900. Launched by Alaska Airlines in 1997 and entering service in 2001, this was the longest stretch of the 737 so far which competes with the Airbus A321. However, as it shares the exit configuration with the -800, it is only certified to carry a maximum of 189 passengers – although this is still a substantial improvement over the basic -800 which typically carries 162 passengers.
On top of the basic variants, there are also specialised versions of these. The first of these is the -700ER, which is somewhat of a hybrid of the -700 and the -800, with the fuselage of the -700 and the strengthened wings and landing gear of the -800. If fitted with the full compliment of auxiliary fuel tanks, this variant can fly an impressive 5775nm, which is around 2700nm further than the standard -700. The launch customer was Japanese carrier All Nippon Airlines in 2007, although the type isn’t particularly common as it’s seen as more of a corporate jet.
A more popular Extended Range variant of the 737 was the -900ER. The type was rolled out in August 2006 and launch customer Lion Air placed the type into service in April 2007. The updates over the standard -900 variant include additional exit doors, meaning the type was certified to carry up to a maximum of 220 passengers and a range improvement to that similar of the -800. This meant the -900ER was far more appealing to customers over the standard -900, outselling it 490 to 52.
By 2010, after the companies long range 787 Dreamliner was a long way into the design phase, Boeing introduced a range of enhancements to the 737 line. From a passenger perspective, the most notable of these is the introduction of the Boeing Sky Interior – featuring larger overhead bins, new sidewalls, new passenger service units complete with personal LED reading lights, and LED mood lighting throughout. Further improvements include 8ft winglets becoming standard in order to improve fuel efficiency and lower noise, exterior LED lighting and the removal of the “eyebrow” windows which had been a feature of the basic fuselage since the 707 entered service in the late 1950’s.
Much like in the 1980’s, by the early 2010’s Airbus had announced an improved version of their popular A320 series, which is the biggest competitor of the 737. Also much like the 1980’s, a major customer of Boeing, American Airlines, placed an order for 130 of the updated A320neo series aircraft. Not wanting to fall behind, the company shelved plans for a completely new aircraft which had been in discussion since 2006 and instead unveiled the fourth update to the now 40 year old 737 design. All was not lost with American Airlines however and despite the airline placing an order for 260 Airbus narrowbody jets, the airline also intended to purchase 100 re-engined 737 jets. By August 2011 Boeing was ready to launch the latest update, dubbed the 737MAX. This new variant once more included updated CFM LEAP-1B engines, updated AT (advanced technology) winglets, which resemble a cross between the original blended winglet of the later 737NG series and the latest split scimitar winglets that were introduced to the NG series in 2014. Also notable improvements include a new tail cone reminiscent of the 787 Dreamliner, extended landing gear to accommodate the new larger engines, a new feature called the MCAS to improve stability due to the larger engines fitter, chevron’s on the rear of the engines, again, carried over from the 787 and various other fuselage improvements. Once more, there was an updated electronic flight deck, loosely based on the previous NG variant. The major selling point of the MAX variant was that Boeing carried enough technology over from the previous NG variant that it wouldn’t need a new type rating for the flight crew or significant training – which would deter airlines as this would add to their costs.
The new MAX variant was rolled out in December 2015, the first flight was made in January 2016, receiving certification from the FAA in March 2017. The launch customer for the MAX variant was Malaysian carrier Malindo Air, the first time since the original 737 that a variant wasn’t launched by a US customer.
Much like previous variants, the MAX series has been developed to replace previous 737 aircraft, by maintaining commonality, and passenger capacity. There are four variants of the MAX series, the -7 which was to have been developed from the -700 although now features the wing and landing gear and wings from the larger -8. Further differences from the previous -700 include a pair of overwing emergency exits, which means an increased passenger capacity, a longer fuselage and an increased range. Despite the improvements over the -700, sales for the -7 haven’t been particularly strong, much like the previous baby of the fleet, the -600. Launch customer Southwest Airlines has pushed back its orders until 2023 at the earliest and WestJet has converted a number of its orders for the -7 into the larger -8. As of 2019, no -7’s are in service and just 60 orders have been placed for the type.
Replacing the most popular 737 variant, the -800 is the -8. This is more or less identical to the -800 but with the MAX updates and an increased range of 3515nm. From 2021, further updates will add a further 100nm on to the total range of the -8. This is the most popular variant of the MAX series so far with close to 3000 orders.
Next in the lineup is the MAX200 – essentially a high density version of the MAX8 which was more or less developed for one of the 737’s best customers, Ryanair. The main differences between this variant and the MAX8 are an additional pair of exit doors to enable the type to be certified to carry 200 passengers and an adjustment of the galley space in order to allocate extra space for more seating. Low cost carrier Ryanair has 135 MAX200’s on order although due to the ongoing grounding of the variant, it is yet to enter commercial service.
The 737-MAX9 is intended to replace the 737-900. Differences from the MAX 8 include a longer fuselage and an enhanced range. Indonesian carrier Lion Air was the launch customer, taking delivery of its first aircraft in March 2018. There has been 250 orders for the MAX9, making it the least popular variant after the -9. Emirates subsidiary FlyDubai will be the variants largest operator, with 70 on order. The types major competitor is the Airbus A321neo.
The final passenger variant of the 737MAX series is the yet to fly MAX10. After major customers United Airlines and Korean Air were pushing Boeing into developing a larger variant than the MAX9, the manufacturer developed this variant to further compete with the A321neo which had well and truly outsold the MAX9. The MAX10 was proposed to include larger CFM engines, stronger wings, revised landing gear, a 7ft stretch to the fuselage. However the compromise with this was a slightly reduced range compared to the MAX9 – the MAX10 will be able to fly 3600mi compared to the 3800mi of the MAX9. However as the design phase continued, it was found that only a modest stretch of the fuselage was needed to seat more passengers than the competing A321neo, therefore the MAX10 was able to keep the wing and engines from the already flying MAX9, therefore reducing the development costs of the new variant. With United airlines slated to be the biggest customer for the MAX10 with 100 due to enter service, the type was slated to enter service in July 2020, however with the ongoing grounding of the MAX series, it remains to be see whether this will still be the case.
2019 saw quite possibly the biggest challenge for not only the 737 series in its nearly 50 year history, but also the Boeing company in general. After two 737MAX series aircraft crashed in similar circumstances within a few months of each other, the 737MAX series was grounded worldwide in March 2019. It was found that the new MCAS (Manoeuvring Characteristics Augmentation System) that was added to the MAX series to automatically counterbalance the plane due to its larger engines causing it to pitch up, was the common factor in both crashes. What shocked many is that there was no mention of this new system in any manuals for the aircraft, and that the pilots knew nothing of this system until the crash of the first aircraft. It has also been reported that this new system could override the pilots input even if it was receiving wrong information from the angle of attack sensor. Initially it was thought that the software updates required would see the MAX series cleared to fly again as early as July 2019, however further issues have arisen therefore delaying the return to service further. My personal opinion is that we wont see the MAX series back in the skies before 2020.
With the current issues facing the 737 line, I think it is about time that Boeing retired the 737 line and developed something new. Remember, the MAX series is essentially a 1960’s design with updated engines almost quite literally shoehorned under the wing and the latest technology in the flight deck and passenger cabin. With the publics dent in confidence following the ongoing grounding of the MAX series, not only to the MAX but the 737 line in general Boeing will have to make some strong decisions in the upcoming years. Its already rumoured as of June 2019 that the MAX name has been dropped by the manufacturer. But will it have to go further and drop the entire 737 line too? One thing is for certain – when the MAX series returns to the sky – and it will return to the skies, as it will simply be far too costly to Boeing to completely bin the project – it will have to be the absolute safest plane in the skies. If it does return to service and something unthinkable happens with a MAX series, even if its related to pilot error, the already low pubic opinion will be completely gone. And if its found to be a technical issue, then that could have far, far worse implications on the whole of Boeing, let alone just the 737MAX line.
All data in this article is correct at the time of writing in June 2019.
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