The Boeing 737 is one of the most successful aircraft in history – and the most delivered to date (although the battle with the A320 family is close). Its latest generation, the 737 MAX, has tarnished its impressive history somewhat. Grounded in 2019 over safety concerns, it has caused difficulties and losses for airlines around the world – as well as for Boeing. It is now flying again, but what does its future hold?
Flying since 1967
Boeing developed the 737 during the 1960s as a supplement and eventual replacement for the popular 727. It was also designed to beat the competition at the time (mainly the Douglas DC-9, but also the BAC One-Eleven and the Caravelle from Sud Aviation).
One of the main changes Boeing made with the 737 was the introduction of just two engines. Its preceding jets (the 707 and 727) were four and three-engine aircraft. Two was seen as the economic way forward, and Boeing responded to the market. Unlike its competition, it chose to mount the two engines in pods under the wings, instead of the rear of the fuselage.
This enabled Boeing to offer a wider cabin, with six across seating (five was typical with other aircraft), and to fit in standard width freight containers. Having the engines lower to the ground also made maintenance easier. This led to issues later, however, when larger engines on the 737 Classic meant the engine bottoms had to be flattened, giving the distinctive ‘hamster pouch’ shape.
The first 737 was unveiled in 1967, and it entered service in February 1968 with Lufthansa. The 737-100 was much smaller than we are used to today, offering a typical two-class capacity of just 85 (with a maximum exit limit of 124). The 737-200 soon followed, with an increased capacity of 102 (with a limit of 136) and higher thrust engines.
Moving through the generations
Boeing has stuck with the 737 since 1967, making modifications and new variants to match changing needs of airlines. Adaptions began early, with an ‘Unpaved Strip Kit‘ allowing landing on gravel runways. This proved popular with airlines in places such as Canada and Alaska. It also developed a convertible passenger to cargo version (the 737-200C).
The Classic series
But it was the movement through several generations, or series, that brought the big changes. Boeing launched the Classic series with the 737-300 in 1984. Keeping commonality with earlier versions was the key here. This saved development and certification costs, as well as time, and allowed airlines to mix fleets easily. Engines were upgraded (to the CFM56), with fuel efficiency improvements.
And size options were widened, with three different capacity variants. The largest of these, the 737-400, took typical capacity up to 188.
The Next Generation series
Improvements in efficiency took another leap forward with the Next Generation (NG) series, launched in 1993 but not entering service until 1997. This was motivated by the development of the A320. It entered service in 1988 and offered more efficiency, as well as full fly-by-wire operation.
Again, the new series maintained commonality but introduced upgraded and more efficient CFM56-7 engines, a re-designed wing, and cabin and cockpit improvements. The number of variants increased to four, and maximum capacity to 200 with the 737-900ER.
The second-largest variant, the 737-800, has gone on to become the best selling so far. Simple Flying looked previously at how the compromise of range and capacity has made it such a success.
Launching the 737 MAX
The 737 MAX Series was announced in 2011 and was introduced in May 2017, with Indonesian airline Malindo Air the launch customer.
Like previous generations, it aimed to incorporate new technology and efficiency improvements whilst maintaining commonality. And like the NG, it also followed an upgrade from Airbus – this time the improved A320neo family (which Airbus launched in 2010, entering service in 2016).
There are, again, four MAX variants. Simple Flying looked in more detail at these differences and prices in a previous article.
| Variant | Capacity | Range |
| 737 MAX 7 | 138 – 153 | 7,130 kilometers |
| 737 MAX 8 | 162 – 178 | 6,570 kilometers |
| 737 MAX 9 | 178 – 193 | 6,570 kilometers |
| 737 MAX 10 | 188 – 204 | 6,110 kilometers |
There is also a 737 MAX 200. This is based on the 737 MAX 8 but with an increased passenger capacity of 200. It has only been ordered by Ryanair, with its order increased to 210 at the end of 2020. There have been delays, but deliveries are expected soon.
Efficiency improvements
Again, engines took a step up in performance and improvement, with CFM International LEAP-1B engines for all variants. Boeing chose a larger fan diameter for these engines, which would further improve efficiency.
But the larger size once again caused issues with its low ground clearance, leading to the lengthening of the nose landing gear and a further forward placement of the powerplants. The engine nacelles have chevrons added for noise reduction, much like the 787.
Other aerodynamic improvements take this efficiency improvement further, most notably its distinctive split winglets.
Winglets work by reducing vortex drag, where different air pressures converge at the wingtips. Over the past years, there have been several different winglet designs with the split winglets first introduced by Boeing as an improvement for the 737 NG. The MAX’s winglets are a new in-house design that Boeing claims improve efficiency even further.
According to Boeing, there is a 14% fuel efficiency reduction between the already improved Next Generation series and the 737 MAX series.
The grounding of the MAX
At the moment, at least, many people remember the 737 MAX not for its efficiency upgrades but for its long and damaging grounding. This followed two fatal crashes:
- Lion Air Flight 610 in October 2018. It crashed in the Java Sea shortly after take-off from Soekarno–Hatta International Airport, Jakarta. All 189 people aboard were killed.
- Ethiopian Airlines Flight 302, in March 2019. It crashed shortly after take-off from Addis Ababa, Ethiopia. All 157 people aboard were killed.
The FAA grounded the MAX on March 13th, 2019 – many other regulators had grounded it even earlier.
Problems with the MAX
The circumstances of both crashes were similar, and it was suspected that problems with the Manoeuvering Characteristics Augmentation System (MCAS) were at least partly to blame. Following the NTSB investigation, this was confirmed.
The MCAS system is designed to move the nose down if an increased angle of attack is detected, to help avoid a stall. The problems that led to the two crashes included erroneous readings from sensors and a lack of training for pilots in how to respond.
MCAS was added to overcome the tendency for the MAX to pitch up, caused by the larger engines and their location further forward. It was not present or needed in earlier 737 generations. This was part of the problem, as Boeing obviously wanted to maintain commonality for the new aircraft.
MCAS ommissions
The addition of this new system was ultimately wrongly handled. Errors included changes to the MCAS plan during implementation (including reducing sensor inputs from two to one) and pressure for Boeing to get the aircraft certified for pilots without simulator training.
This training issue – both the omissions of MCAS for conversion training and the plans needed for it going forward – has been a major issue in the investigation and re-certification plans.
In its conclusions, The NTSB report said:
“That Boeing used in its functional hazard assessment of uncommanded MCAS function for the 737 MAX did not adequately consider and account for the impact that multiple flight deck alerts and indications could have on pilots’ responses to the hazard … The specific failure modes that could lead to unintended MCAS activation (such as an erroneous high AOA input to the MCAS) were not simulated as part of these functional hazard assessment validation tests.”
A costly problem
CNN refers to the MAX grounding as “the most expensive corporate blunder ever.” While we are not going to compare it against others, it was certainly extremely damaging for airlines and Boeing.
Airlines sued Boeing for losses incurred. And there have been extensive costs for repairs to the aircraft. Boeing estimates it has incurred a direct cost of $20 billion due to the MAX grounding. This includes $8.6 billion paid to airlines in compensation. This does not include compensation and legal liability for the crash victim’s families.
Added to this are loss of sales and reputational damage to Boeing. With the aircraft grounded, customers waiting for the 737 MAX did not have to pay cancellation fees for retracted orders, and several airlines have taken advantage of this during the pandemic slowdown.
Getting airborne once again
The FAA issued guidance to repair the aircraft faults and improve pilot training in August 2020. It was cleared to resume service (subject to changes and training) in November 2020. The Canadian and European regulators cleared it in January 2021.
Flights resumed in December 2020, with American Airlines making a demonstration trip. The first commercial service flew on December 9th with Brazilian airline GOL (from Sao Paulo to Porto Alegre), and American Airlines flew the first US service on December 29th.
United Airlines resumed services in February. Southwest Airlines, the type’s largest customer, followed in March.
Many other airlines are resuming the type more slowly. With the ongoing slowdown, there is no rush to supplement aircraft already flying.
Lost orders
The grounding and the slowdown in aviation have taken their toll on orders. Before this, the MAX was proving popular. By January 2019, Boeing had recorded just over 5,000 orders for the MAX. Orders have since been lost though, despite Boeing’s attempts to sell some of these white tails to other airlines.
In 2019, it lost 93 orders. And in 2020, 641 were lost. More have been lost when changes to accounting standards are taken into account. 2021 has been mixed, with some orders lost, but also new orders picking up. Deliveries were halted during the grounding but have now resumed.
Simple Flying took a look at the largest customers in March 2021 (following this shake-up). Southwest Airlines remained up front, with 380 firm orders (200 737 MAX 7s and 180 MAX 8s). This includes an additional order for 100 aircraft placed in March.
Lion Air and flydubai are tied following this, with 251 orders. And Ryanair has 210 MAX 200 aircraft on order, including an order for 75 placed last December.
As of late April 2021, Boeing has 3,965 unfilled 838 MAX orders. And in total, 472 aircraft have been delivered.
Future for the 737
The problems may not all be over for 737 MAX, though. In April 2021, Boeing recommended 16 MAX operators look at a potential electrical issue before returning aircraft to service, effectively grounding 106 aircraft. Around the same time, the US Transportation Department’s Office of Inspector General said it would again audit the FAA after the decision to unground the type.
A new mid-sized aircraft?
Looking further ahead, what might be the next developments for the 737? One of the most discussed new aircraft is the Boeing NMA (New Midsize Aircraft), also dubbed the 797. This was originally seen as a replacement for the 757, sitting between Boeing’s offerings of the 737 MAX and 787 Dreamliner. These plans were dropped in 2020, largely due to the issues and losses from the 737 MAX.
With Airbus launching the A321XLR, Boeing could look again at its NMA plans. A new narrowbody design that builds on the 737 MAX is one option for this. Additional fuel tanks could offer the extra range needed, but the MAX 10 is already sized to the limit. Without significant and expensive re-design, passenger capacity would suffer.
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Alternatively, Boeing could make updates to the 757 or 767. A 757 MAX could seat around 240 passengers and offer improved range and efficiency with new engines. A 767 MAX could re-engine the original widebody with the General Electric GEnx.
The 737 has had a long history and is going nowhere soon. Commonality has been the key to this success but also a major contributor to the MAX’s issues and grounding. This article has given an overview, but there is a lot more to the 737 MAX’s story. Feel free to discuss further in the comments.