Boeing test pilots discovered during the pre-production test flight, that 737MAX8 was difficult to handle when its speed dropped below a certain point. At certain speed, aircraft enters into an aerodynamic stall, and loss of control that could lead to a crash.
In order to mitigate the problem, Boeing introduced a new system called Maneuvering Characteristics Augmentation System,(MCAS). Pilots flying more than 200 MAX8s in service, claim that they were unaware of MCAS.
The MCAS system came to media attention after Boeing released a Bulletin on MCAS, after the Lion Air 737MAX8 Flight 610 crash investigation began.
The Aerodynamic stall issue started when Boeing adopted new larger and fuel efficient engines for 737MAX8. The 737MAX8 structural design was originated from 1960s 737 design. The 737s sits lower to the ground (short landing gear) than other Boeing models. To install larger engines without making a major design change, Boeing engineers, moved the engines slightly forward, and lifted it up and lengthen the nose landing gear by 8 inch. The location of the engines caused an upward pitching movement at certain airspeed and triggered aerodynamic stall. To solve the issue, Boeing introduced MCAS under part 25 certification.
The 737s were designed to sit lower so that baggage and cargo to be hand-loaded from the tarmac without mechanical assistance., because Boeing’s intention was to bring jet services for small airports that were not fully equipped to load cargo. However, this innovation swiftly became pointless as airports became better equipped.
Since 737 became the best-selling single-aisle jet in history and Boeing’s most enduring cash cow, Boeing decided to introduce variants without making major design change.
Normally an aerodynamic stall is indicated by “stick shake” and pilots are trained to instinctively increase speed and push the nose down to recover stability.. but Boeing decided to Automate the stall recovery by introducing MCAS, that will sense the stall and moves the horizontal stabilizer to pitch down the nose. Engineers apparently did not anticipate the possibility of other inputs, in this case, angle of attack sensor, could initiate the MCAS, unknown to pilots.
Though pilots claim that they are unaware of MCAS, most of the Automated systems are not revealed to pilots as they not required to understand or even know about – unless they turn out to have a potentially dangerous role in some circumstances.
Who is flying the plane? the systems or human… the debate goes on…