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Russ Niles | February 3, 2019

A New York Times investigation of October 29, 2018, Lion Air Boeing 737 MAX suggests that the marketing considerations were at least partly behind the joint decision of Boeing and the FAA not to specifically train pilots in the system. Increased maneuver characteristics (MCAS) that may have played a role in the accident. The Times story cites several sources with names that say Boeing wanted to maintain cross-compatibility between the new aircraft and previous versions of the 737, simplifying conversion training and reducing costs for airlines that buy the MAX.

The difficulty was that the physically larger engines that comply with the aircraft's main point of sale (better fuel economy) had to be mounted higher and farther forward than in its predecessors and that significantly changed the characteristics of low speed flight . The MCAS was designed to compensate for the higher tendency of the MAX to stop in a low speed turn by adjusting the angle of the horizontal stabilizer. The system takes data from one of the two attack angle indicators (there is no requirement for redundancy or agreement) and was designed to automatically push the nose down if an incipient blockage was detected. Boeing convinced the FAA that because the system maintained the basic flight characteristics of the previous versions, the pilots did not need specific training on the MCAS, although their inclusion was considered necessary for the certification of the aircraft.

The Times story also points out that other regulators, at least initially, determined that pilots should know the MCAS. European regulators wanted the pilots to be trained in this, but eventually accepted the position of the FAA and Boeing. Brazil, however, maintained its weapons and required specific training for MCAS pilots.

Boeing did not hide the addition of MCAS. It is described in the operation and maintenance manuals and explained at the technical information meetings with potential customers. It also included an emergency checklist that covered the disqualification of the system. But because they were not specifically trained in its use, most pilots did not know that it was there and that it operated in a manner fundamentally different from the speed adjustment system that operated the stabilizer configuration in the previous 737s. It should be noted that pulling the yoke back on older aircraft deactivates the automatic adjustment. The withdrawal does not deactivate the MCAS in the MAX.

Something the Times could not determine was whether the MCAS was tested in fault mode, either in the simulator or on the aircraft itself. The prevailing theory about the root cause of the accident was that erroneous AOA data resulted in an erroneous and extreme reaction of the MCAS, which led the aircraft to a high-speed dive from which the pilots could not recover. Boeing and the FAA are being investigated by the National Transportation Safety Board and Indonesian authorities to determine whether the decision to skip pilot training in the new system played a role in what became the worst air crash of 2018.