Boeing’s Own Test Pilots Lacked Key Details of 737 MAX Flight-Control System – The Wall Street Journal

Investigators have linked faulty sensor data to the flight-control system’s misfire, which led to crashes in Indonesia and Ethiopia that took 346 lives.

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The extent of pilots’ lack of involvement hasn’t been previously reported and could bring fresh scrutiny from investigators and regulators already looking into Boeing’s design and engineering practices. It isn’t clear whether greater pilot participation would have altered the ultimate design of the flight-control system. But the scaling back of pilots’ involvement and their lack of detailed knowledge about the plane’s system add to the list of questions about engineering and design practices facing the Chicago-based aerospace giant.

A Boeing spokesman said test pilots and senior pilots didn’t have less of a role in the design, briefing and testing of the final version of MCAS when compared with their counterparts who worked on previous models featuring important new systems.

“Listening to pilots is an important aspect of our work,” the spokesman said. “Their experienced input is front and center in our mind when we develop airplanes. We share a common priority—safety—and we listen to them carefully.”

The MAX fleet has been grounded world-wide since the second crash in March, while Boeing and the Federal Aviation Administration complete a software fix to make MCAS less potent and have it rely on dual sensors. Chief Executive Dennis Muilenburg recently told investors Boeing would examine how it could improve the process of developing airplanes.

Boeing’s test pilots are an elite full-time crew, usually consisting of former military aviators, who try out systems on new aircraft before engineering specifics are locked in. Such test flights occur before the final version of the airplane is produced, cockpit procedures are set and the aircraft is delivered to customers.

Boeing’s management has long prided itself on close collaboration between test pilots and engineering staff. For decades, and particularly through the development of the first version of the wide-body 777 in the early 1990s, Boeing talked up how its roster of pilots and commercial aviators specifically recruited for feedback provided suggestions about the model’s cockpit design and function.

“The test pilots have to be fully aware of what those capabilities are, and how the airplane will respond in those situations because they are ultimately the judge and jury,” a senior Boeing executive said recently.

After Boeing decided to develop the MAX in 2011, executives overseeing the program welcomed and acted upon pilots’ suggestions, including adding larger cockpit displays, a senior pilot involved in the process said. Any suggestions that touched on safety got full attention, this pilot said.

But over time, an internal restructuring that began in 2009 introduced changes in that process, eventually reducing pilots’ clout, according to people familiar with pilots’ role in the process. Boeing had consolidated its testing and evaluation teams into a companywide group of pilots and labs to streamline operations as it kept a lid on costs. The teams had previously worked independently within Boeing’s commercial and defense divisions.

About midway through the MAX’s development, the senior pilot recalls warning a Boeing executive about taking pilots out of the loop: “Something is going to get by, and it’s not going to be pretty.”

The senior Boeing executive said he hadn’t heard such concerns and defended the consolidated testing group. The restructuring added no additional cost pressure for testing, he said, and instead strengthened the group by making more resources available across the company.

The MCAS system was a new addition to Boeing’s 737 series, meant to kick in automatically and operate in the background to prevent a plane from stalling. A stall can occur when a plane is flying too slowly and its nose is too high to maintain lift. In the MAX, MCAS uses sensor data about the plane’s angle to push down its nose and keep it from stalling.

One former Boeing pilot who participated in some later-stage MAX test flights recalls hearing about MCAS in a general way, but wasn’t given further details. For instance, this pilot never learned about the system’s reliance on a single sensor transmitting data about the angle of a plane’s nose, or how far MCAS would be able to move a plane’s adjustable tail fin known as a “horizontal stabilizer,” which controls the up-and-down movement of a jet’s nose.

Test pilots did have the opportunity to try out the MAX and its automated system under various scenarios, but those didn’t include testing the full force of MCAS, some of these people said. Looking back, some pilots contend Boeing could have missed design flaws given their cohort’s at times limited involvement in the craft’s development.

In 2016, a year before the MAX began commercial service, some test pilots suggested adapting MCAS, initially designed to operate at high speeds, to also work when the plane was traveling at slower speeds, according to one of the people familiar with the matter. By then, test pilots had less say in how design revisions were implemented. They also weren’t told explicitly that in its final iteration, MCAS commands would be four times as powerful than in earlier versions, according to people familiar with the matter. That change was earlier reported by the Seattle Times.

In hindsight, test pilots “had no real input” into the ultimate MCAS design, one of the people said.

Senior Boeing pilots at times found themselves excluded from meetings involving engineers, prompting them to sometimes invite themselves or show up unannounced, according to this person. The senior Boeing executive said last week that current development programs aren’t characterized by such friction.

Write to Andrew Tangel at and Andy Pasztor at


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