The many human errors that brought down the Boeing 737 Max

The first sign of problems appeared right after takeoff.

Inside the PK-LQP cabin, a new Boeing 737 Max belonging to Lion Air, the stick vibrator on the captain's side began to vibrate. Stick agitators are designed to warn pilots of an impending stop, which can cause a dangerous loss of control. They are unmistakably noisy for that reason.

But the plane was flying normally, nowhere near a post. The captain ignored him.

Approximately 30 seconds later, he noticed an alert on the screen of his flight, IAS DISAGREE, which meant that the flight computer had detected sensor malfunction. This required a little more attention.

A passenger plane today looks less like a race car and more like a temperamental printer: you spend more time monitoring and reviewing the systems that actually drive the thing. So the captain passed control of the aircraft to the first officer and began the process of solving problems from memory.

Like all commercial aircraft, the Boeing 737 Max has multiple levels of redundancy for its important systems. In the cockpit, there are three flight computers and digital instrument panels that operate in parallel: two primary systems and one backup system. Each system is powered by an independent set of sensors. In this case, the captain checked both instrument panels against the backup, and discovered that the instruments on his side, the left side, were obtaining erroneous data. So with the turn of a dial, the captain changed the primary screens to use only data from the work sensors on the right side of the plane. Easy.

All this took less than a minute, and everything seemed to return to normal.

At 1,500 feet altitude, the takeoff part of the flight was officially completed, and the first officer began the initial climb. He adjusted the throttle, placed the aircraft on its optimum ascent slope and removed the fins.

Except that the plane did not go up. He staggered down, his nose pointed to the ground.

The first officer reacted instinctively. He flipped a switch on his control column to counter the dive. The plane responded immediately, raising its nose again. Five seconds later, he dived again.

The first officer raised the nose of the plane for the third time. He threw himself down.

There was not a memorized checklist that seemed to apply to this situation, so the captain looked for the Airplane Quick Reference Manual (QRH). The QRH is a series of simple checklists that are designed to help pilots quickly assess and manage "non-normal" situations. The idea is that Boeing has thought of all the possible things that could happen to one of his planes, and has included them all in the QRH. Basically, it's more problem solving.

But nothing in the QRH seemed to apply, either.

For the next six minutes, when the first officer struggled to control the plane and the captain searched for the correct checklist, the PK-LQP climbed and dove a dozen times. At one point, the plane retreated from a 900-foot dive at an airspeed of nearly 375 mph, which is uncomfortably close to the "red line" of the 390-mph 737.

The flight crew had to solve something quickly before losing control of the plane.

Then, the third person in the cockpit, who was technically out of service, "dead heading" to his next task, reportedly spoke.

What about the runaway stabilizer checklist?

It was a shot in the dark, another checklist. "Clipping out of control" occurs when some type of failure causes the horizontal stabilizer of an aircraft to move, or "cut", when it should not move at all. In general, this creates a constant upward or downward force that the flight crew must try to counter during the rest of the flight. It is something like trying to drive when the wheels are not aligned.


the many human errors that brought down the boeing 737

Leak stabilizer checklist for the Boeing 737 Max.
Image: Preliminary Aircraft Accident Investigation Report, Lion Air Flight 610

The problem of PK-LQP was a bit different. It was intermittent, temporarily reversible, and it was not even clear if the horizontal stabilizer was causing the problem. But they were running out of options. They followed the checklist and switched the STAB TRIM to CUT OUT switches in the center console.

The plane stopped. Five seconds passed. Then five minutes. Once again, PK-LQP was under his control and out of danger.

An hour later, flight 043 of Lion Air landed in Jakarta, Indonesia, with only a few minutes delay. Following the standard procedure, the captain reported the episode to the airline, and the airline's maintenance team verified serious equipment failures and found none.

The next morning, PK-LQP, which operated as Flight 610 of Lion Air, took off at 6:20 a.m. local time on its way to Pangkal Pinang, Indonesia. His shaker was activated right after takeoff. He launched multiple errors on the flight screen. He dove right after the flight crew withdrew their wings. And he relentlessly activated his automatic tone adjustment in the nose-down direction 28 times over the course of eight minutes.

This time, there was not a third pilot to help the flight crew.

PK-LQP may have reached 600 mph, faster than a Tomahawk missile, as it launched into the water. It was the first accident of 737 Max in his 18 months of service.

Lion Air Flight Telemetry

For outsiders in the industry, it was a shock. What could have knocked down one of Boeing's newest and most technologically sophisticated aircraft? But those closest to the development of the plane knew better: there were warning signs from the beginning.

The Verge spoke with a dozen pilots, instructors, engineers and experts on the 737 Max and its development, implementation and the two crashes that have claimed the lives of 346 people. What emerged was a history of cascading failures: the many small human errors in each phase of the design, certification and operation process of the airplane. These errors reached a terrible and deadly climax in the skies over the Java Sea in October 2018 and over the Ethiopian countryside five months later.

Max's story is, ultimately, the history of the Darwinian business cycle in which mature companies like Boeing face constant threats of new products, new competitors and the quest for new growth. Sometimes this motivates them to new heights of innovation and progress. Other times, he asks them to withdraw everything in the name of cost cutting.


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The events that led to these two fatal crashes were launched almost a decade ago, and began not with Boeing, but with the company's European rival, Airbus.

Boeing 737 and Airbus A320 are the two main players in the massive and massively profitable market of narrow body passenger planes. Together, both aircraft comprise almost half of the world's 28,000 commercial aircraft. Most likely, if you've ever flown somewhere, you've flown in one of them.

Both manufacturers face a race to lower their airplanes so that airlines can operate, especially when it comes to fuel.

In 2018, for example, Southwest Airlines' 751 Boeing 737 fleet consumed 2.1 billion gallons of fuel at an average cost of $ 2.20 per gallon, for a total of $ 4.6 billion. A 1% increase in fuel efficiency would save $ 46 million. That's nothing to sneeze, even for a company that got $ 2.5 billion in net profits.

Therefore, Airbus and Boeing constantly adjust their aircraft to squeeze a single percentage point out of them But full reviews are rare: the 737 received one last in 1997, with the debut of the third generation 737NG, while the A320 had not been renewed since its launch in 1988.

Then, on December 1, 2010, Airbus Surprised the aviation community. In secret, he had developed a more efficient version of the A320 called A320neo (which means "new engine option"). It would burn around 6 percent less fuel than the 737NG. That was an impressive leap in fuel efficiency, given at a time when the price of jet fuel reached a near record of $ 2.50 per gallon.

The airlines loved it. The following summer, at the Paris Air Show 2011, the equivalent of the Black Friday aerospace industry, Airbus sold a record of 667 A320neos in the span of a week. That was more orders than those who had received the 737 in the whole of 2010.

Boeing was captured with flat feet. He had spent four years debating the future of his narrow-body jet program, and he still did not have an answer to his most basic question: whether Boeing should make a completely new design or renew the 737 once again.


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Faced with the existential threat of the A320neo, Boeing executives decided in a matter of weeks. The company would launch a fourth-generation 737, and it would do so in record time.

The 737 Max was, clearly and simply, a provisional measure.

Boeing could save billions of dollars in engineering costs by basing the Max off of the 737 platform. That gave the company an advantage in design and engineering work, enough, Boeing expected, to allow the Max enters into service only a few months after the A320neo.

But the project engineers would have to overcome some monumental challenges to be able to comply in time. The first was the 737 platform itself. It would take a considerable amount of work to update a 46-year design with all the technology it needed to be as efficient as the competition.

"The 737 was conceived in the 1960s as what we would today call a regional aircraft, and with each variant, they have pushed and pushed the thing to the end of its envelope," says Patrick Smith, an airline pilot and blogger in Ask the Pilot . "It makes you wonder if the platform they're working with is so outdated at this time."

At the same time, designers could not update too much too much. By law, a pilot can only fly one type of aircraft at a time. However, the Federal Aviation Administration allows different models of aircraft with similar design characteristics to share a common "type certificate". So, for example, the three previous generations of the 737 have a common type certificate. When you qualify in a model, you can all fly.

This allows airlines with common type fleets to more easily replace pilots and aircraft, which makes their operations more flexible. As a result, many airlines are limited to one manufacturer's aircraft over the other. Some, like Ryanair and Southwest, only operate a single type of aircraft for maximum operational efficiency.


  Boeing holds a press conference addressing the 737 MAX software and training update

A Boeing employee works outside the booth of a Boeing 737 Max 8 aircraft at the company's factory.
Photo by Stephen Brashear / Getty Images

It also encourages manufacturers to design aircraft that obtain these common type certifications. However, a type certificate is so detailed and complete, ranging from the dimensions of the aircraft to the configuration of the passenger cabin and the way the aircraft moves and sits during the flight, which can limit the amount of people who have designers when they try to add a new model. to an existing certificate.

The Max, for example, not only had to be similar to the 737NG of the previous generation, which was launched for the first time in 1993, but also had to be sufficiently similar to the 737 Classic of 1980 and the original 737 of 1964. In essence, it had to be a 21st century vanguard aircraft that still felt and flew like the ones designed when the Beatles were still together.

Boeing took six years to do all this, one year less than necessary to develop the 777, and 18 months less than the 787. To beat Airbus, it would have to break the only unbreakable law of project management: that a development cycle could be fast, cheap, and . If it failed, Airbus could hoard a $ 35 billion market for single-aisle aircraft for a decade or more.

So Boeing could not afford to fail.


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The first signs were encouraging. With two years of development, Boeing promised that the Max would be 8% more fuel efficient than the A320neo. Five and a half years later, the FAA granted Max its Modified Type Certification. Only a few months later, the program's main pilot, Ed Wilson, boasted that pilots classified in previous versions of the 737 could switch to Max with only "2 and a half hours of computer training."

This was another key point of sale for airlines: there is no expensive class time, no expensive simulator time. In theory, pilots could read about Max at home, take a self-administered computer course in the morning and be ready to fly in the afternoon.

Therefore, between its fuel and training efficiency, Max looked like a winning prospect. for everyone, especially Boeing, who sold a record $ 200 billion worth of Maxes before the first prototype hit the skies.

The skilful public relations campaign masked a design and production process that extended to the breaking point.

Designers drew planes at twice their normal rate, often sending incorrect or incomplete schemes to the factory. Software engineers had to settle for the recreation of 40-year analogue instruments in digital formats, instead of innovating and improving them. All this was done in order to keep Max within the limitations of its common type certificate.

and many pilots felt that, for the first 737 new in more than 20 years, Boeing seemed strangely reluctant to prepare them for it.

Captain Laura Einsetler, who has flown for more than 30 years, even in the 737, considers that a fully computer course is completely inadequate as an introduction to a new plane.

"I do not have the schemes, I do not have the cab panels, I do not have an instructor I can ask questions about," she says. "You expect the first time you see Max on a clear and pleasant day, but sometimes not, and you show up at night or in bad weather on a plane that has all these changes."

There was something else that Boeing had not mentioned about the 737 Max. Eight days after the Lion Air accident, a newsletter appeared on MyBoeingFleet, the airline's online portal for pilots and airlines. It read:

"Boeing wishes to draw attention to a [Angle of Attack] fault condition that may occur only during manual flight ."


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The first public recognition of Boeing by MCAS, through a technical bulletin published after the Lion Air accident.
Image: Preliminary Aircraft Accident Investigation Report, Lion Air Flight 610


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In soft technical jargon, Boeing described the exact series of events that brought down the PK-LQP. The confusing series of alerts. The sudden dives. The fact that this "failure condition" would continue to occur until, unless the crew changed the STAB TRIM, it changes to CUT OUT, as the crew had correctly guessed on the penultimate flight of PK-LQP.

The presence of this system, lurking somewhere in Max's software suite, was shocking enough. Even more frightening, Boeing only provided the minimum information to airlines and pilots. The bulletin did not give a name to the system or explain what it was designed for its normal operation. He just said that sometimes it works badly, and that he can crash his plane.

"It was a bit like," Okay pilots, good luck with that, find out ", says Einsetler.

For four days, angry pilots and airline officials bombarded Boeing with demands for more information. Finally, on November 10, another message appeared on MyBoeingFleet:

"Boeing received many requests for the same information from 737 fleet operators," he said.

Finally, Boeing admitted what the world feared: something was fundamentally wrong with the new 737 Max.


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The culprit was the Maneuver Characteristics Increase System (MCAS). Like the 737 Max, MCAS was made to be a provisional resource.

The Max was designed around a new set of engines called LEAP-1Bs. These are much more efficient than the engines of the 737NG, but they are also much heavier and larger.

This created a design problem. The engines in the NG are only 18 inches off the ground, and the assembly of the LEAP-1B in the same place gave them very little clearance during takeoff. So Boeing placed them further and slightly higher in the Max's wing.

That solution created an aerodynamic problem. Due to their size and position, the Max engines create lift when the aircraft enters a steep climb (or, in the language of aviation, at high attack angles). This additional increase causes the Max to be handled differently than previous versions of the 737, but only when it is climbing.