By Nalliah Thayabharan

Boeing currently maintains a 40% market share, while Airbus dominates the other 60% of the industry. Both of these firms hold incredible leverage over the entire airline industry, allowing them to maintain a somewhat relaxed relationship with oversight bodies like the FAA.

The first ever Boeing 737 entered service 56 years ago in 1968.

Ending the production of the 737 with the NG or Next Generation family – 737NG,  Boeing 737 would have still been in production for over 50 to 52 years, making it a true aviation icon with more than 10,000 aircraft built.

But instead, in August of 2011, Boeing decided to launch yet another re-engined version – 737 MAX.

Why did Boeing stop making the 757, but not the 737?

Why Boeing chose to launch Boeing 737 MAX 9 which was involved in two tragic crashes in 2018 and 2019 ?

Boeing didn’t pick the 737 over the 757. In the mid 2000s, Boeing actually intended to replace both of those aircraft with new ones.

The Boeing 737 just stayed in production for a little bit longer, because Boeing still had orders for it and kept getting more, whilst that wasn’t the case for the Boeing 757.

During that time, the nemesis of the Boeing 737 was the Airbus A320 family, and in the 1990s, Boeing had actually designed the Boeing 737NG just to make sure that they could compete with the Airbus A320 family successfully, which the Boeing NG also did.

But both Boeing and Airbus knew that newer, better engine technologies were just around the corner by then, with both CFM and Pratt & Whitney working on designs that would be able to achieve double-digit percentages of efficiency gains.

For Airbus, the choice was relatively simple, at least on the technical side. In 2010, the Airbus A320 had only been in service for around 22 years, meaning that there was still plenty of life left in it, so a re-engined version seemed like the obvious way to go.

Also, besides being younger, the Airbus A320 family has a taller landing gear, meaning that it sits much higher off the ground than the Boeing 737 family does, giving it much more room under its wings for larger diameter Turbofan engines. Now that’s super important, because newer, more efficient turbofan engines all have a bigger diameter for a larger fan, which is needed to achieve higher bypass ratios and those double-digit efficiency gains.

For the Boeing 737 however, the re-engined option was much less attractive as it sat low close to the ground like its ancestor, the Boeing 727, had done, and it had been constructed in that way in order to make boarding and disembarking with air stairs easier and also to facilitate manual ground handling.

In the years since though, manual ground handling  had just basically stopped being a factor, because basically all smaller airports eventually got the baggage handling equipment that they needed.

Anyway, this low stance meant that fitting larger turbo fan engines to the Boeing 737 wasn’t going to be easy. Boeing had actually already struggled to fit the first CFM56 Turbofan engines to the Boeing 737 Classic back in the 1980s, where it had required fitting the engines further forward of the wing instead of under it, like on the original 737s.

And even after doing that, those CFM56 Turbofan engines engines themselves had to be changed in order to fit the Boeing 737. That’s the reason why they have that noticeably flat bottom, which gives them another few inches of ground clearance, and because of that redesign, several other systems also had to be relocated inside of the engine.

But even after that, the fan diameter of those engines still had to be made smaller than on other versions of the same CFM56 engines.

In the 1990s, the Boeing 737NG family then got a further improved CFM56 with a slightly larger diameter, which required even more modifications of the engine, the pylons, and some other systems.

Now, the engines on the Airbus A320 still had a larger diameter and a higher bypass ratio than those on the 737NG, but Boeing still managed to make the 737NG competitive with the Airbus, but only just.

Now, obviously, any further re-engine attempt would involve using even larger engines on an aircraft that simply wasn’t made for them.

So why would Boeing even consider that?
Well, the answer is that another 737 re-engine would allow the aircraft manufacturer to avoid something that Boeing’s CEO at the time, Jim McNerney, called a moonshot.

Most explanations around why Boeing developed the MAX instead of an all-new aircraft concentrate on a large aircraft order made by American Airlines, who surprised Boeing by selecting the Airbus A320 over the 737 back in 2011.

This happened after Airbus had announced its decision to re-engine the Airbus A320 family and at that time, Boeing had basically decided
on designing an all-new aircraft instead.

But that surprise order by one of the largest and most loyal customers forced them to instead abandon those plans and quickly refocus on developing another 737.

Now to be clear, that explanation isn’t completely wrong. Before hearing about the American Airlines deal, Boeing’s engineers and a lot of the company’s management really had been favoring an all-new airplane, which would borrow a lot of fresh technologies and features from their brand new Boeing 787.

In February of 2011, over four months before that American Airlines contract, Boeing’s CEO, McNerney, told analysts, “We’re going to do a new airplane instead of a re-engined 737,” although he then clarified that the final decision about that hadn’t really been made yet.

Then American Airlines forced Boeing’s hand, except there are a couple of really important details missing from that explanation. Airbus had pursued that deal with American Airlines specifically to force Boeing to re-engine the 737NG.

In 2010, when Airbus decided to re-engine their A320s, the 2008 financial crisis had just happened, a few years before and it was less than a decade after 9/11.

So with the financial reality that existed at the time, Airbus weren’t sure if they could even afford to develop an all-new airliner. But if Boeing decided to go ahead with an all-new plane, Airbus would have no choice but to do the same.

Airbus believed that an Airbus A320neo would be much more efficient than a 737 with newer engines, which as it turns out wasn’t quite true, but there was no question that an all-new Boeing aircraft would be even more efficient, making the Airbus A320neo obsolete.

This strategy was a gamble for Airbus, because if Boeing hadn’t taken the bait and instead gone ahead and designed a new plane, then they would be caught between a rock and a hard place literally.

But this is where the idea that the American Airlines order was the decisive factor in Boeing’s decision-making starts to make a little bit less sense.

Losing an order for 200 planes from a loyal airline customer was a big deal, but we’re talking about aircraft designs for the very heart of the market, with potential production runs of over 10,000 jets.

Those types of aircraft pay back for their investment over many decades, not by a single order, so would it really be worth risking such a long-term strategy only on this?

Well, this is where we get back to the then Boeing CEO, Jim McNerney, and his aversion to moonshots. A moonshot is what McNerney called the design of a new aircraft.

Boeing’s decision to make what we now call the 737 MAX came just after the 787 was about to enter service after what had been a very problematic development, full of delays and cost overruns.

The 787 had been supposed to enter service faster and cheaper than Boeing’s previous all-new widebody, the 777, but that hadn’t happened, and McNerney wasn’t in the mood for a repeat of that process.

McNerney’s motto for Boeing at the time was More for Less, which applied to his view towards suppliers and workers, but as it turns out, also towards aircraft development.

Every 25 years a big moonshot, and then produce a 707 or a 787 is the wrong way to pursue this business.

The more-for-less world will not let anyone pursue moonshots.

The thought of just squeezing the last bit of water out of every rock instead of boldly looking forward and solving new problems is almost always the penny-pinching beginning of the end for the leader of any industry.

When you stop innovating and start relying on only defending old wins, you basically start dying.

But as for the 737 MAX, it looks like that American Airlines order came at just the right time, or wrong time, to sway Boeing’s board back towards a re-engined 737.

The way that decision came has led some to assume that Boeing rushed the development of the MAX in order to beat Airbus, because when Boeing learned of the imminent Airbus contract, their sales teams scrambled to come up with this new plane’s key details, contract terms and conditions in just one day.

When all of this was happening, Boeing had been studying and comparing the performance of a 737 re-engine versus a new plane for many years. Boeing’s efforts to squeeze bigger engines under the 737’s wings had not started with the MAX. So they probably thought that they knew what they were doing when that decision was taken.

Another important detail in Boeing’s choice was the fact that many airlines really wanted a re-engined 737 instead of an all new aircraft.

American Airlines, Southwest and many others were keen to get a newer and more efficient version of the aircraft that they already knew, but there was a catch to that.

Those airlines would only really want another 737 if Boeing could promise to make it really easy for their pilots to transition over to it. That had actually been a key point for Airbus and its A320neo family.

For their pilots, the new version would basically fly exactly like the existing A320s.

Sure, the new engines came with some new procedures, but those could be taught without the pilots spending any time in a simulator, which was super key. So that’s what the airlines wanted to hear from Boeing too.

All 737s apart from the very first 737-100 and 200 models can be operated on the same pilot type rating, so that’s what the airlines now also demanded from the MAX.

But even for aircraft variants within the same type rating, there is often a requirement for what we call difference training, which often also can involve some simulator training.

The airlines really wanted to avoid that if at all possible.

So in other words, they wanted pilots to have been trained to fly on the 737NG to be able to transition directly over to the 737 MAX with only some computer-based training or CBT, basically a training session that the pilots could complete at home with an iPad.

If Boeing could pull this off, airlines would be able to immediately use their existing pool of 737 pilots for this brand new variant, and these pilots would then be able to switch back and forth between all the new 737 variants as well, which is a super big deal, since it would take many years for an airline with 737NGs to fully transition over to a whole MAX fleet.

Again, Airbus already offered this to their airline customers who were ordering A320neos, but the A320 is a fly-by-wire aircraft which can be programmed to mimic the flight characteristics of another variant using just some code.

That’s very handy, since another requirement that aircraft have to satisfy in order to keep the same type rating is that they share almost exactly the same handling characteristics.

Now again, this is obviously something that Boeing had had to deal with before,since the 737 has changed and grown a lot over the decades, but in the case of the MAX, this is where we get to the part in this story that many people think they understand, but most really don’t, the Maneuvering Characteristics Augmentation System, or MCAS.

The CFM LEAP-1B engines of the 737 MAX are bigger than the previous CFM56s are, and this meant that they, again, had to be moved slightly more forward and further up in front of the wing than the previous engines.

But contrary to what you might have heard, the engine position of the 737 MAX does not make the aircraft unstable. Actually, aside from some military jets, all aircraft have their center of gravity in front of the center of pressure of the wing.

So having more weight further forward actually makes the plane more stable, not less.

However, it is true that under certain conditions,like when the aircraft was flown at high angles of attack, those large, flat-bottomed engine nacelles actually started producing a certain amount of lift.

And while that lift was not enough to make the aircraft unstable, it did change the feel of the aircraft’s control slightly. In technical terms, it changed something known as the stick force gradient.

The aircraft would still fly fine, it wouldn’t be any more prone to stalls or anything, but in these very specific circumstances, when the aircraft was flown manually at high angles of attack and with flaps up, its yoke would feel slightly lighter than the yoke of a 737NG. So that just needed to be sorted out.

But what if something could trim the aircraft’s nose forward a bit under these circumstances, trim it to effectively cancel out that lightness in the controls and make the airplane behave more like any other 737?

As it happened, Boeing had recently developed another aircraft that needed exactly this kind of system.

And this was the KC-46A Tanker, which was basically a military 767 freighter.

Now, thanks to its use as both a tanker and a freighter, the KC-46 was created to be able to fly with a wider center of gravity envelope than a regular 767 and it, therefore, required this MCAS system as well.

After Boeing’s engineers decided to include this system in the MAX, it was originally only supposed to be available at higher speeds and with a very small trim input, which is what the original specifications given to the FAA also said.

But Boeing’s test pilots soon found that it probably was needed at slower speeds as well, so the scope of the system kept growing.

This meant that MCAS went through a number of evolutions as Boeing’s engineers and test pilots tested the aircraft’s handling during development, and that meant that while the FAA knew of the existence of MCAS in its original version, they didn’t know what it eventually became.

And what it eventually became was quite disturbing. The idea was that if the aircraft was placed under the conditions that would activate MCAS, then the system would operate just once to simulate that stick force and it would then reset itself when the pilots trim the aircraft manually.

But in practice, the fact that the system reset itself also meant that it would be able to repeat its input again and again and again, if the underlying activation criteria was still sensed.

And not only that, but in low-speed situations, Boeing had allowed each trim input from MCAS to be a staggering 2.5 degrees, which is a very substantial input and more than what a pilot would trim in one go under most circumstances.

On top of this, when a risk assessment was made, the risk that MCAS was deemed to have after failure was initially deemed as major on a scale including minor, major, hazardous and catastrophic.

And since major was on the bottom half of that scale, MCAS was deemed safe to form part of the normal speed trim system, which was already fitted to the 737, and that was a system that relied on only one single angle-of-attack sensor at the time.

So what ended up happening with the version of the MCAS that first entered service was that an erroneous activation would not only trim the plane’s nose down again and again, but each activation could also be bigger than the opposite trim that the pilots would be comfortable with inputting, leading to a successively higher and higher nose down trim.

And this could all be triggered by a single fault in one single sensor.

The way that the system was supposed to work with a small single activation would have represented a risk akin to a cat in a cage in a room. But with these potentially repeated large activations, it added up to something akin to a loose tiger in a room instead.

Boeing believed that this system would be activated very rarely. It would only come on during manual flight, with the flaps retracted and at high angles of attack, which almost never happened, so functionally, as a system, Boeing didn’t think that it was a really big deal.

Even if something did go wrong, they thought that the pilots would quickly recognize the problem and react in time to fix it by first inputting the opposite elevator, then stopping the movement with their trim switch and finally, if needed, disabling the whole system with the stabilizer trim cutout switches.

And that was already part of something known as a runaway stabilizer non-normal checklist, used if the stabilizer trim would start misbehaving.

But in order to react on time, the pilots would have needed to know that this system existed, and initially, at least, pilots didn’t, because Boeing left the details of MCAS out of the MAX manuals.

Why did Boeing do all of these things? Why did they cobble together a system like this and why did they keep it secret from the plane’s pilots?The FAA has come under a lot of scrutiny for allowing Boeing to do this and rightly so, but why did Boeing and its employees go along with it in the first place?

Obviously, the motivation behind all of these decisions was to make sure that no SIM training would be required for existing 737 pilots in order to fly on the MAX, but the company’s culture, at this point, meant that they prioritized meeting deadlines and commercial commitments like no SIM training over basically everything else.

And a series of emails between Boeing test pilots and other employees who were released in the aftermath of the crashes made this clear to everyone.

Now, initially, a lot of people placed the blame for the MAX crashes with the airlines as well as with the pilot training in Indonesia, Ethiopia and elsewhere.

Lion Air had actually been uneasy about letting their pilots fly on the MAX without simulator training. So in 2017, over a year before the first MAX crash, they had asked Boeing for an option to do so.

And Boeing’s employees found this request alarming. They quickly rushed to shut down this idea so that it wouldn’t create a precedent for others to follow and actually, a few weeks earlier, Boeing’s chief technical pilot had indicated in another internal memo that the company expected requests for SIM training to come from regulators, not from the airlines.

He said that the company will not allow that to happen, and will go face to face with any regulator who tries to make that a requirement.

After the first MAX crash, a lot of airlines reached out to Boeing for information about MCAS, since remember they didn’t previously even know that this system existed.

One of those airlines was Ethiopian, whose chief pilot emailed Boeing’s chief pilot, asking specifically what to do when confronted with multiple faults and how to prioritize them.

Now after receiving that, multiple Boeing employees had an email discussion on how to respond to this very direct technical series of questions
and basically, their approach reads like an effort to reply to the Ethiopian Airlines chief pilot in the most vague way possible, citing the ongoing investigation of the first crash.

And, of course, Ethiopian Airlines was then going to be the next airline to suffer a devastating crash. Boeing had a very different attitude towards pilots from the US-based airlines, which made comparisons between pilots around the world even less meaningful and just added to the resentment towards Boeing.

The released emails are full of insulting comments towards Boeing, towards the FAA and the airlines, quite extreme even considering that they were never meant for publication.

But more importantly here, these emails revealed just how little faith Boeing’s own people had in the way that the company was operating.

Perhaps the most famous line was that the newest 737 was designed by clowns who, in turn, are supervised by monkeys.

But it’s quite clear that a lot of Boeing workers understood where the basis of the problem was.

Someone else had written,
“I don’t know how to fix these things. It’s systemic. It’s culture. It’s the fact that we have a senior leadership team that understand very little about the business and yet are driving us to certain objectives.”

Anyway, going down the rabbit hole of all Boeing’s decisions which led to the design of MCAS and everything else around it is something that the FAA and other regulators have been trying to do for over five years, because we do need to know that this cannot happen again.

But it is equally important to understand that Boeing did fix MCAS. It’s now connected to two angle-of-attack sensors which will kill MCAS if they feel that they disagree, and the system is now only able to activate once per flight, never more.

So it now really is that cat in a cage that we talked about before and that it was always supposed to be.

Boeing 737 pilots today do simulator training to learn how to fly the MAX and how to deal with problems that they might encounter, including more detailed training around the speed trim system, how the aircraft will react and feel with and without MCAS, and how to deal with any anomalies.

The 737 Max is so much more efficient than the NG, but it does take so much time to start the engines, but that’s a different story.

But these disasters was also the reason why the industry reacted so strongly in January of 2024 when the door plug blowout happened to an Alaska Airlines Boeing MAX 9, because that showed that Boeing still had some potential problems to fix in their culture, which is why they have undergone so many management changes since then.

On May 5, 2007 Kenya Airways flight 507-  a Boeing 737-800 carrying 108 passengers and crew members tragically vanished from radar and crashed leaving no survivors – the shock of this disaster echoed around the world shaking confidence in Boeing. In the wake of this tragedy China saw an opportunity to rethink its approach to Aviation while Boeing’s 737 series continued to soar alongside Airbus China quietly began plotting a new course determined to reduce its Reliance on foreign manufacturers and motivated by the need for safer, more reliable alternatives.

The Comac C919 is a narrow-body airliner developed by Chinese aircraft manufacturer Comac. The development program was launched in 2008 to break the Boeing and Airbus duopoly by introducing a narrow body jet that could stand shoulder to shoulder with Boeing 737 MAX and Airbus A320neo family. Production began in December 2011, with the first prototype being rolled out on Nov 02, 2015; the maiden flight took place on May 05, 2017. On Sept 29, 2022 the C919 received its CAAC type certificate. The first production airframe was delivered to China Eastern Airlines on Dec 09, 2022 and was put into commercial passenger service on May 28, 2023.

The aircraft, primarily constructed with aluminium alloys, is powered by CFM International LEAP turbofan engines and carries 156 to 168 passengers in a normal operating configuration up to 5,555 km. In 2023, COMAC announced that it would develop both a shortened and a stretched version of the passenger jet – similar to the sub-variants offered for the competing Boeing 737 MAX and Airbus A320neo family.

The COMAC CJ-1000A engine is a new jet engine that has been developed by the Commercial Aircraft Corporation of China (COMAC) for use on its C919 narrow-body airliner. This advanced engine is a game-changer in the industry, featuring cutting-edge technology and superior performance.

The COMAC C919 is China’s homegrown airliner which is hoped to offer an alternative to the Boeing/Airbus duopoly in this section of the market. The CJ-1000A engine is pivotal to making this an all-Chinese product.

One of the key features of the CJ-1000A is its high-bypass ratio. This means that a larger percentage of the air passing through the engine is used to generate thrust, rather than being used to cool the engine or provide other ancillary functions. This makes the engine more efficient and reduces fuel consumption, which is a major benefit for airlines looking to save money on operating costs.

In addition to its high-bypass ratio, the CJ-1000A also utilizes advanced materials and manufacturing techniques. The engine’s fan blades, for example, are made from a composite material that is both lighter and stronger than traditional materials. This allows the engine to be more efficient and reliable, while also reducing maintenance costs over the life of the engine.

The CJ-1000A also features a state-of-the-art digital control system, which constantly monitors and adjusts its performance. This system ensures optimal efficiency and reliability at all times, making it easier for maintenance crews to diagnose and repair any issues that may arise with the engine.

The modular design of the CJ-1000A allows for sections of the engine to be replaced rather than the whole engine having to be removed for maintenance or repair.

The CJ-1000A is being developed for the Comac C919 narrow-body airliner with a thrust of 98 to 196 kN. It has a diameter of 1.95 m and a length of 3.29 m. It uses a similar two-spool configuration to the General Electric LEAP-1C, with a one-stage fan, three-stage booster, 10-stage high-pressure compressor, two-stage high-pressure turbine and six-stage low pressure turbine. Its 18 wide-chord fan-blades are made of hollow titanium like those of Rolls-Royce engines and its single annular combustor uses 3D printed fuel nozzles.

The COMAC CJ-1000A engine is a cutting-edge piece of technology that offers superior performance and efficiency, and is poised to be used on the C919 airliner, which is set to make waves in the aviation industry. As the first aircraft designed and built entirely in China, the C919 represents a major milestone for COMAC and the Chinese aviation industry as a whole.