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Boeing defends deactivation of safety feature in 737 MAX

written by Denise McNabb | April 30, 2019

A file image of a Boeing 737 MAX flight deck. (Boeing)
A file image of a Boeing 737 MAX flight deck. (Boeing)

The blowtorch was turned on Boeing at its annual general meeting on Monday (US time) after details emerged over the weekend about the deactivation of an optional safety feature on its 737 MAX jets that might have alerted pilots to malfunctions in angel of attack (AOA) sensors.

US carrier Southwest Airlines released a statement in the US that said Boeing did not disclose the deactivation of the safety feature on its 737 MAX aircraft until a Lion Air 737 MAX 8 crashed in Indonesia on October 29 2018.

The carrier was reaffirming an article in The Wall Street Journal on Sunday that Southwest, along with the Federal Aviation Administration (FAA) inspectors and supervisors were also unaware of the changes. The FAA has not commented.

Southwest said that the safety feature was “depicted to us by Boeing as operable on all MAX aircraft” but did not tell the carrier the feature was not turned on until after the crash, CNBC reported.

The alert tells the pilot if an angle of attack indicator is transmitting bad data about the plane’s nose pitch. The sensor was operational in previous 737s but, according to Southwest, was switched off in the 737 MAX.

US television network CNN also reported four Boeing employees called an FAA whistleblower hotline to report damage to the wiring of sensors, and that Boeing made airlines pay extra if they wanted an alert that let pilots know if two sensors were contradicting each other.

Disgruntled shareholders expressed concern over a 10 per cent drop in value of Boeing’s share price following the grounding of the MAX after the March 10 crash of Ethiopian Airlines that killed all 157 passengers and crew on board.

A file image of the Boeing 737 MAX tail and winglets. (Boeing)
A file image of the Boeing 737 MAX tail and winglets. (Boeing)


And preliminary reports suggest similar circumstances caused a Lion Air 737 MAX 8 to crash, killing all 189 on board in Indonesia in October 2018.

As Boeing chief executive Dennis Muilenburg fronted the annual meeting at the Field Museum in Chicago, the company issued a response to the news over what it called a “disagree alert”.

The statement said Boeing did not intentionally or otherwise deactivate the alert on its MAX airplanes.

“Boeing included this disagree alert as a standard feature on the MAX, although this alert has not been considered a safety feature on airplanes and is not necessary for the safe operation of the airplane,” Boeing said.

Boeing said the alert was tied or linked into the angle of attack (AOA) indicator, an optional feature on the MAX.

“The disagree alert was intended to be a standard, stand-alone feature on MAX airplanes. However, the disagree alert was not operable on all airplanes because the feature was not activated as intended,” it said.

“Unless an airline opted for the angle of attack indicator, the disagree alert was not operable.

“The air speed, attitude, and altitude displays, together with the stick shaker, are the primary flight information indicators in the flight deck. All recommended pilot actions, checklists, and training are based upon these primary indicators, not on the AOA disagree alert or the angle of attack indicator.”

Boeing, however confirmed that when the 737 MAX returned to service after software modifications were approved and certified, all MAX production aircraft will have an activated and operable disagree alert and an optional angle of attack indicator.

“All customers with previously delivered MAX airplanes will have the ability to activate the disagree alert per a service bulletin to airlines,” Boeing said.

At a media conference after the annual meeting, Muilenburg said the pilots did not “completely” follow the procedures that Boeing had outlined to prevent the kind of malfunction that probably caused the March 10 crash of an Ethiopian Airlines 737 Max.

The airframer has acknowledged previously that the anti-stall software, known as the Manoeuvring Characteristics Augmentation System (MCAS), was activated in response to erroneous angle of attack (AoA) information in both the Ethiopian Airlines and Lion Air tragedies, following the publication of the preliminary report into the Ethiopian Airlines accident.

Muilenburg said MCAS met Boeing’s design and safety criteria and adhered to certification protocols. Further, Boeing had been unable to find any “technical slip or gap” in building its MCAS software.

“When we design these systems, understand that these airplanes are flown in the hands of pilots,” Muilenburg said.

“Going forward we have identified a way to improve.

“We know this is a link in both accidents that we can break.

“We’ve been in constant contact with our customers and listening to their needs to ensure that the fleet is maintained appropriately and positioned for an efficient return to service once cleared for passenger flights.

“Our teams will take an entry into service approach with every plane returning to service which includes deploying teams to all of of MAX operators and providing dedicated real time operational support.

“Through the work we are doing now in partnership with our customers and regulators to certify and implement the software update the 737 MAX will be one of the safest airplanes ever to fly.”

Boeing’s financial results for the first quarter of calendar 2019 released on April 24 showed earnings fell 21 per cent amid the ongoing impact of the 737 MAX crisis.

Muilenburg started the annual meeting with a moment of silence for those killed in the two crashes.

“We feel the immense gravity of these events. There is nothing more important to us than the safety of our people who fly on our airplanes,” he said.

“Every day 5.3 million people fly safely on Boeing airplanes.

“On average more than 2,900 737 airplanes are in the air with nearly half a million passengers on board at any given time. A 737 takes off around the world or lands roughly every 1.5 seconds.”


Muilenburg escaped a bid by shareholders to separate his hats as both chairman and chief executive with only 34 per cent voting in favour of the move, well short of a majority.

He affirmed Boeing was getting close to a software fix. It had completed 146 flights of the 737 MAX with the updated software, totalling around 246 hours of flight time. The chief executive flew on two of the test flights.

A small group of protesters stood outside the meeting holding large photos of some of the people killed on the two flights.


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