Boeing left out a 737 Max safety feature linked to its fatal crashes, despite including it on an earlier plane, report claims

boeing 737 max ethiopian airlines

REUTERS/Baz Ratner

An Ethiopian police officer walks past debris of the Ethiopian Airlines Flight ET 302 plane crash in March 2019.

  • Boeing left a safety feature off the software on its 737 Max planes that was present in an earlier version of the system, The Wall Street Journal reported.
  • The anti-stall software system, called MCAS, misfired in the two fatal crashes that killed 346 people, pointing the noses of both planes down into dives from which they never recovered.
  • The system relied on a single external sensor - a design widely criticised by experts.
  • But a military jet designed before the Max used MCAS with multiple sensors, sources told the Journal.
  • Boeing said in response that the two systems "are not directly comparable."
  • However, part of the company's proposed fix for the 737 Max includes data from a second sensor.
  • Visit Business Insider's homepage for more stories.

Boeing left a safety feature off the software system on its 737 Max planes that was linked its two fatal crashes, despite including it on an earlier version of that system used elsewhere, a new report claims.

The version of the automated anti-stall system, called MCAS, on the 737 Max relied on data from only one of the plane's two angle-of-attack sensors, which measure the plane's angle in the sky.Advertisement

In this plane, the system worked with multiple sensors - giving the pilots more control over the plane, according to the report.

Boeing 737 Max planes

David Ryder/Getty Images

Undelivered Boeing 737 Max planes sit idle at a Boeing property in Seattle, Washington, in August 2019. The planes cannot be flown by their airlines as the plane has been grounded around the world since March.


Boeing confirmed in April that an erroneous sensor readings triggered the plane's MCAS software in the two fatal crashes: a Lion Air flight in Indonesia in October 2018 and an Ethiopian Airlines flight in March 2019 in Ethiopia. The crashes killed a total of 346 people.

Preliminary reports from investigations into the two crashes suggested that there were problems with the sensor readings.Advertisement

In both flights, the planes nosedived and pilots were unable to regain control.

lion air plane crash

Eddy Purwanto/NurPhoto via Getty Images

Objects recovered from the sea at Tanjung Priok Port, Indonesia, after the Lion Air Boeing 737 Max crash in October 2018.

The MCAS system is designed to prevent the aircraft from stalling - which can occur when a plane is angled too sharply up - by automatically pointing the nose down.Advertisement

Experts have criticised Boeing's decision to have the plane rely on just one sensor input.

Peter Lemme, a former Boeing flight-controls engineer, told CNN in May that the plane should have had "a fail-safe design" that "relied on two inputs to make sure that you weren't sensitive to one failure."

Read more: As the FAA head defended the agency's handling of the Boeing 737 Max, he suggested that the agency might change its process for certifying new planesAdvertisement

US Rep. Peter DeFazio, the chair of the House Transportation and Infrastructure Committee, also said that his committee's investigation into the 737 Max would look at how its software relied on a single sensor.

Boeing 737 Max cockpit

Ted S. Warren/Associated Press

The cockpit of a Boeing 737 Max plane.


Boeing has since defended its design. In response to the CNN report, a spokesperson said that "single sources of data are considered acceptable in such cases by our industry."

The plane will not fly again until regulators in the US and around the world approve Boeing's fixes - a process that most in the industry do not expect to be completed until the end of 2019 at the earliest.Advertisement

Sources for The Wall Street Journal said this fix will make the MCAS system in the Max plane more similar to the one in the military jet.

Read more: 400 pilots have joined a growing number of airlines in demanding payback from Boeing for its 737 Max disasters - here's the full list

A Boeing spokesman declined to explain to The Wall Street Journal why the systems are different on the two planes. The spokesman said said: "The systems are not directly comparable."Advertisement

Boeing 737 Max ethiopian airlines family

REUTERS/Baz Ratner

Kenyans mourn family and friends, who were victims of the Boeing 737 Max Ethiopian Airlines plane crash, at the crash scene in March.

An Air Force official and other unnamed sources told the Journal that the military refuelling jet with the MCAS system also has another safeguard, which lets pilots override the system by pulling on the controls.

Will Roper, an assistant Air Force secretary who serves as the branch's procurement chief, said: "We have better sensor data."Advertisement

Max pilots have criticized Boeing for what they described as a plane design that lessens their control over the plane, in ways they say they were told of in advance.

Read more: The Boeing 737 Max could be grounded through the holidays thanks to a series of new delays, and airlines are cancelling thousands of flights because of itAdvertisement

American Airlines pilots confronted Boeing executives about the MCAS system in November 2018, after the first crash but before the second.

Boeing is currently facing lawsuits from the families of those killed on the planes, as well as federal investigations and demands for compensation from airlines around the world who have had their planes grounded and unable to fly since March.Advertisement

The 737 Max has 'no value' after 2 deadly crashes as passengers no longer trust the plane, the lawyer for an aviation firm suing Boeing says

Get the latest Boeing stock price here.