Reuters / Jason Redmond
Under scrutiny.
AOA DISAGREE

A cockpit warning light for a mechanical fault in the 737 Max was an optional add-on

By Rosie Spinks

All eyes are on the investigation of the black box from Ethiopian Airways flight ET 302, currently being analyzed by officials in France. What has yet to be determined is whether the cause of Sunday’s crash is related to Boeing 737 Max’s maneuvering characteristics augmentation system, or MCAS, which was implicated in the investigation into the Oct. 2018 Lion Air crash in Indonesia.

The system is designed to nudge the nose of the plane down to prevent it from stalling when necessary. It does this automatically, based on the aircraft’s angle of attack (AOA) data, or the angle of the aircraft’s wing relative to the flight path. However, in the event of a faulty AOA reading, the system will nudge the plane downward unnecessarily, and could eventually cause it to crash. As reported by the New York Times, a software fix for the system was promised by the end of 2018. After this week’s crash, it’s being promised for April. 

But according to reports, the Lion Air plane did not have an optional feature installed in the aircraft—one that Boeing doesn’t provide as a standard feature and costs additional money to install—which would have alerted crew that the AOA readings were erroneous and likely to trigger the MCAS system unnecessarily. That’s because Boeing and the FAA didn’t require what was called the “AOA DISAGREE” alert be installed for safe operation of the 737 Max.

Reuters reported in November that several airlines, including American Airlines, Southwest Airlines, Canada’s WestJet, SilkAir and flydubai, had the alert installed before the Lion Air crash. It’s unclear whether Ethiopian Airlines did. Separate from the alert, some have also asked why Boeing didn’t provide more training to pilots so that they would know how to counteract the MCAS system if necessary.

As Jon Ostrower of The Air Current wrote about the investigation into the Lion Air flight, the aircraft’s “angle of attack sensors were disagreeing by 20 degrees as the aircraft taxied for takeoff. A warning light that would have alerted the crew to the disagreement was not part of the added cost-optional package of equipment on Lion Air’s 737 Max aircraft. A guardrail wasn’t in place. Once the aircraft was airborne, the erroneous angle of attack data collided with apparently unprepared crew with tragic consequences as the MCAS system repeatedly activated, driving the jet’s nose into a fatal dive.”

A professor Embry-Riddle Aeronautical University told Reuters after the Lion Air crash in November that, “In retrospect, clearly it would have been wise to include the warning as standard equipment and fully inform and train operators on MCAS.” The professor, Clint Balogm, added that he expected to see “this warning included in future MAX production and retrofitted into already delivered MAX aircraft.”

Update: An FAA spokesman responded to Quartz’s questions about why it did not require the “AOA Disagree” alarm feature as a standard safety feature on the Boeing 737 Max 8, but rather allowed it to be an optional add-on with a statement saying, “The FAA’s aircraft certification processes are well established and have consistently produced safe aircraft designs. The 737-MAX certification program followed the FAA’s standard certification process.” Boeing, when reached by Quartz, declined to comment.

Read more of Quartz’s coverage of the Boeing 737 Max crisis.