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Boeing 737 Max – The essentials


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The second fatal crash of Boeing’s latest aircraft, the B737 Max 8, in Ethiopia on 10 March has reverberated all over the world.

The Max is the latest iteration of Boeing’s classic 737 design that first flew in 1967 and is the world’s bestselling jet airliner, with over 10,000 built to date. The Max accounts for nearly 50% of the world’s ‘narrow-body’ jet aircraft fleet, which are used for most regional flights.

An effective duopoly

The Boeing Company (NYSE:BA) is the world’s oldest and largest aerospace company, having been founded in 1916. With a market cap of over $ 200 billion and revenue of over $101 billion, Boeing is one of the largest aerospace companies in the word. It reported an operating profit of $7.9 billion in FY 2018 and its shares reached an all-time high of $ 440.62 on 1 March. 



Boeing’s key rival is the European aerospace giant Airbus (NASDAQ:EADSY) and between the two players they have 98% of the world’s commercial jetliner market. However, Boeing is the more profitable entity, as it has a robust defence business as well. 

While Boeing dominates the large ‘wide-body’ market with the 777 and 787 models, the 737 is the company’s cash-cow selling the largest number of units. The venerable 737 however, has been gradually losing market share to Airbus’ A320 offering in the ‘narrow-body’ market. 

This accelerated in 2011, when Airbus decided to upgrade the engines on the A320 family with more advanced and fuel-efficient power plants, marketed as the Airbus 320 New Engine Option or NEO.

The Airbus 320 NEO left Boeing with a dilemma. Should they invest in a long and probably very expensive development program to build a new narrow-body aircraft with latest technology and ‘fly by wire’, or try to upgrade the existing model with new engines and a few tweaks to keep it current?

The dilemma faced by Boeing

The 787, which Boeing had launched in 2004 but only delivered in 2011, had cost an estimated $32 billion in development and manufacturing. Prolonged delays and technical problems on the 787 had cost the company dearly and profit-hungry executives were not eager to engage in a similar expensive program in such a short time span.

It was decided to avoid developing an all-new aircraft, but instead upgrade the 737 with similar engines to what the A320 would have (the CFM –LEAP) and make a few more modifications to keep the aircraft competitive. By doing so, Boeing executives hoped to save costs and get the aircraft to market much sooner. Critically, it also allowed Boeing to market the aircraft as a ‘variant’ of the B-737, thus keeping the same pilot ‘type-rating’. 

This path would avoid the lengthy certification process that every new aircraft type must undergo, to prove that it is safe as well as efficient. Pilots who were currently flying the 737 could also fly the Max with just a self-study course, with no expensive simulator training and conversion needed, as it was designated a ‘variant’ and not a completely new type.

This represented a huge saving for the airlines, particularly the US giants who had 737 fleets numbering in the hundreds. Pilots could fly the Max and earlier versions interchangeably, reducing the cost of introducing the aircraft, while at the same time enjoying a 15-20% fuel saving for the new type.

A runaway sales success

The Max proved to be a winner. Sales were strong, with over 4000 sold in a short while. But behind the scenes Boeing engineers were facing an impossibly tight design deadline. The Max was launched in 2011, offered for sale in 2012 and the first completed aircraft was rolled out in 2015. By the standards of the aviation industry, this was astonishingly fast. It certainly saved Boeing a lot of money. It also meant that Airbus did not dominate the narrow-body market with their NEO – Boeing kept a roughly equal market share with the Europeans.

The Max was one of the factors that led to Boeing being Wall Street’s darling, with the high price of Boeing’s shares helping to pushthe NY Stock Exchange to record highs.

The hidden threat

But as we now know, the Max had at least one fatal flaw. The bigger and more powerful LEAP engines were positioned further forward than on the older 737s, making the aircraft fly differently to earlier versions. This meant that, in an extreme case of nose-up aircraft attitude, the Max was in danger of entering an unrecoverable ‘stall’.   



While this is an unlikely scenario, certification rules demanded that in order to prevent this, Boeing’s engineers had to create a new software ‘patch’ they labelled MCAS (Manoeuvring Characteristics Augmentation System). 

MCASwas designed to push the aircraft’s nose down automatically in the event of an extremely nose-high attitude being detected, with the sole purpose of avoiding a stall. The system was intended to make the pilots ‘feel’that the 737 Max (which was now much heavier and behaving differently to its previous generation) handled in same way as the older aircraft the pilots were familiar with. 

Crucially, the Max was certified without the pilots being explicitly made aware that MCAS even existed. The Federal Aviation Administration (FAA) and the European Aviation Safety Authority (EASA) viewed the augmented system as a minor modification and did not require that Max pilots were made aware of its presence. 

The only dissenting voice was the National Civil Aviation Agency of Brazil, who insisted that Max aircraft registered in that country specifically addressed MCAS and made the pilots aware of it. 

Crucially, the ‘angle of attack’ (AoA) information that MCAS relied on was fed by a single sensor and this information was not visible to the pilots unless the airline paid extra for an optional display. Boeing has since agreed to make this feature available as standard, with no extra charge. It is a sad indictment of the company and the regulators that it took two fatal accidents and over 300 deaths to make this happen. 

These two crashes will go down as a tragic failure on the part of not only Boeing but also the FAA, which was hitherto the most respected aviation regulator in the world, to exercise due care in the development and certification of airliners.

Fatal consequences

On 29 October 2018, Lion Air flight JT610 a 737 Max took off from Jakarta and crashed into the Java Sea shortly thereafter. The preliminary accident report released in January showed that the MCAS system created an excessive nose-down control input, even though the aircraft was not close to stalling. 

In a chain of events that led to the situation, which is yet to be definitively asserted by the investigators, the behaviour of the MCAS system was driven by the malfunctioning of a critical ‘angle of attack’ sensor that was feeding information to MCAS. 

In this situation, MCAS appears to have pushed the aircraft repetitively into a nose down mode – in order to avoid the ‘stall’ which it perceived. The aircraft was not close to stalling – the lack of redundant information sources meant one faulty sensor activated MCAS erroneously. 

Lion Air had not opted for the AoA display and since the existence of MCAS was not part of the pilot training program,the crew was unable to correct the situation. The aircraft dived into the sea, killing all on board.

The accident of a practically brand-new aircraft caused shock waves throughout the industry, and initial analysis centred on the little-known MCAS addition. However, the aircraft type was not grounded but continued to be manufactured and fly all over the world.

That is, until the tragically similar accident of Ethiopian flight ET302 in March, which also crashed just after take-off in eerily similar circumstances. This caused China’s aviation regulator (CAAC– the second biggest Max user), to ground the aircraft. This decision cascaded through the industry and subsequently a worldwide grounding of the Max fleet coming into operation. 

Sadly, America’s FAA that most respected of regulators, was the last to ground the Max, a fact that has further sullied its reputation and led to charges of collusion between the powerful industry giant and its governmental watchdog.

What’s next?

Boeing continues to manufacture the 737 at the rate of almost 54 aircraft a month. The integrated supply chains and ‘just in time’ manufacturing techniques mean that production cannot be stopped in the short term.

The FAA and Boeing are working hard at a fix to the MCAS issue and are expected to release a software update in a few days’ time. It is reported that the AoA information will now be fed to MCAS from both sensors and that the information will be displayed to the pilots as a standard fit. Initial tests in the simulator indicate that pilots are now coping with a failure of MCAS competently.

This will probably allow the Max to start flying again soon but recovering passenger confidence is going to take a long time. With over 300 already built and 4000 more on order, the airline industry desperately needs the Max to become airworthy as soon as possible, certainly before the peak summer travel season begins.

The fundamental issue

At the heart of the problem is that the 737 is still a mechanical aircraft. An overlay of modern instruments and software tastefully obscures the fact that underneath the aircraft floor, steel wires and pulleys are still at the heart of the 737’s flight control system. This is in stark contrast to Boeing’s own 777 and 787 family, where the flight control system (being fly-by-wire) has minimal mechanical components. 

As per information available at this time, the MCAS system created a nose down input –without much knowledge to the pilots – based on readings which it receives from the sensors. 

The MCAS’s inputs to the aircraft’s flight controls meant that the pilots, who were not aware of the system’s existence, needed to be constantly focused on the aircraft’s surroundings and behaviour and be able to react swiftly and promptly. It is now estimated that the Lion Air crew had less than a minute to correctly diagnose the problem, an impossible ask when they did not know that MCAS even existed.

Fly-by-wire changed the industry

30 years after the introduction of fly-by-wire airliners, there has been an exponential growth of the industry, with a superb safety record. Today, there are less than a 100 fatalities per trillion kilometres flownby the worldwide industry, an astonishing record that has been improving year on year. 

This astonishing safety record, the benign behaviour of the newer aircraft and the rapid growth in airlines has, however, led to some compromises. Pilots have slowly adapted to the new technology, becoming increasingly focussed on following Standard Operating Procedures and the automated failure identification systems that are integrated to the design of today’s aircraft.

For the Airbus fleet, which is entirely fly-by-wire, these systems work very well. Boeing wide-body products, the 777 and 787 are also fly-by-wire. The venerable 747 is not, but with production diminishing, this type will slowly become obsolete soon.

The issue is, of course, the 737 Max. No amount of software fixes can change the fundamentals of the mechanical flight control system which is at the heart of this type.

To draw an analogy with the automotive industry, most of today’s airliners are like a Toyota Prius or perhaps a Tesla. The electronic systems are an integral part of the design and the operator (or pilot/driver) has little visibility as to how they interact with each other. One must accept that they are well designed and will function flawlessly, as they do.

The Max however, may look like a Prius but under the sophisticated veneer, it is actually an old Corolla with a manual transmission. The electronics may resemble a more modern aircraft, but the fundamentals of the system dates to the 1960s, when it was first designed.

The writer, a pilot with experience on 12 different types of jet aircraft, feels that it is time the industry reverts to the basics as well. The return of the Max to commercial while will happen and the regulators, having learned a bitter lesson, will ensure that it is safe. But it is vital that the industry look further than just a fix to this particular issue.

Pilots gradually becoming ‘systems operators’ has been the subtle trend industry-wide. We have obviously gone too far in this direction. In the case of the 737 Max there will have to be a large and dedicated investment in training pilots to fly again, not rely on the automated systems to keep them safe. There may well be other, hitherto unknown, issues lurking deep with the aircraft’s systems. It is only by dedicated training of the very basic flying skills, can we insure that the travelling public can be confident of that the system is a safe as we can make it.


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