Boeing close to issuing safety warning on 737 Max

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Aviation regulators such as the FAA and the European Aviation Safety Agency often follow such actions by mandating that carriers follow the bulletins - something the FAA says it will do in this case.

On Tuesday, Boeing issued a safety bulletin for airlines operating its new 737 Max airliner in the wake of the crash.

"This emergency AD was prompted by analysis performed by the manufacturer showing that if an erroneously high single angle of attack (AOA) sensor input is received by the flight control system, there is a potential for repeated nose-down trim commands of the horizontal stabiliser", the AD, issued on Wednesday evening (US time), reads.

Boeing said in its statement that it had issued an operations manual bulletin (OMB) to 737 Max operators that advised flight crews to turn to existing procedures "where there is erroneous input from an AOA sensor".

Signs appear to point to an instrument failure in the brand-new Boeing 737 Max, specifically the angle-of-attack sensor, which is critical to determining the amount of lift generated by the wings.

Under some circumstances, the Max jets will automatically try to push down the nose if they detect that an aerodynamic stall is possible.

However, this new reminder from Boeing raises questions about the pilots' actions, how the flight crews are trained and if the maintenance that was performed was adequate.

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The pilot of the flight requested a return to Denpasar but the situation corrected itself and he elected to continue to Jakarta. The agency said the pilots were dealing with an erroneous airspeed indication.

A crucial sensor that is the subject of a Boeing safety bulletin was replaced on a Lion Air jet the day before it plunged into the Java Sea and possibly worsened other problems with the plane, Indonesian investigators have revealed.

The night before the fatal crash, the same aircraft had erratic speed and altitude issues during a flight from Bali to Jakarta, it emerged yesterday. The jet is the latest in Boeing's long line of hot-selling 737 family of narrow-body airliners.

For example, over 10,000 Boeing aircrafts flying around the world have used parts and components made in China and Chinese firms have participated in the manufacturing of all Boeing's aircraft types, including the 737, 747, 767, 777 and the most innovative 787 Boeing 787 Dreamliner.

Both Boeing and the FAA are continuing to assist Indonesian officials in investigating the accident. The aircraft system that handles the nose up and down movement (called stabilizer trim system) will put the nose down in response to the erroneous AOA sensor.

The Angle of Attack sensor, shown to reporters at a press conference in Jakarta on Wednesday, was manufactured by Minnesota-based Rosemount Aerospace Inc. In the early days of the jet age, the elevator trim system was linked to several accidents.

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