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737 MAX 8
An artist’s conception shows the Boeing 737 MAX 8 jet. (Boeing Illustration)

Boeing says it has issued an operations manual bulletin to address concerns about erroneous readings from a sensor that has been implicated in last week’s fatal crash of a Lion Air 737 MAX 8.

The jet dove into the Java Sea at high speed on Oct. 29, minutes after its takeoff from Jakarta in Indonesia. All 189 people aboard the plane were killed. Safety investigators said that pilots on the plane were dealing with inaccurate airspeed readings and asked to return to the airport just before the crash.

Boeing’s newly issued bulletin focuses on the 737 MAX’s angle-of-attack sensors, or AOA sensors, which are supposed to provide data about the angle at which wind is passing over the airplane’s wings. Boeing said the action was taken after the Indonesia’s National Transportation Safety Committee indicated that the Lion Air jet experienced erroneous input from one of those sensors.

In a statement released late Tuesday night, Boeing said the bulletin directs operators to “existing flight crew procedures to address circumstances where there is erroneous input from an AOA sensor.”

Earlier this week, investigators said the plane’s flight data recorder showed that an airspeed indicator malfunctioned during last week’s fatal flight as well as three previous flights. The head of Indonesia’s National Transportation Safety Committee, Soerjanto Tjahjono, told reporters in Jakarta on Monday that he was discussing the options for wider inspections with Boeing and his U.S. counterparts.

In advance of Boeing’s brief statement, sources told Bloomberg News and The Air Current that the recommended procedures are meant to handle issues related to the potential for a stall.

Under some circumstances, a 737 MAX jet could automatically push down its nose if it detects that a stall is possible, based on the angle of attack. Erroneous readings from the AOA sensor could push the plane into an aggressive, unwarranted dive. This issue is said to arise only during manual flight.

The Air Current’s Jon Ostrower quoted an unnamed industry official as saying the flight crew procedures call on pilots to use the electric stabilizer trim to reverse the downward push, while keeping in mind that the nose could push downward again five seconds after the switches are released.

To avoid having the problem repeat, pilots may deactivate the automatic stabilizer trim system, according to The Air Current’s explanation.

Boeing’s statement suggested that further steps lie ahead.

“The investigation into Lion Air Flight 610 is ongoing and Boeing continues to cooperate fully and provide technical assistance at the request and under the direction of government authorities investigating the accident,” the statement said.

The Federal Aviation Administration said it would put regulatory weight behind Boeing’s bulletin by issuing an airworthiness directive on the angle-of-attack issue.

“The FAA continues to work closely with Boeing, and as part of the investigative team on the Indonesia Lion Air accident, will take further appropriate actions depending on the results of the investigation,” the agency said in a statement.

This is an updated version of a report that was first published at 7:42 p.m. PT Nov. 6, 

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