For a full year, Boeing knew that a safety indicator on its Max 8 planes would remain inactive due to incompatible software, but only issued a global bulletin in the week following the first crash of a Boeing Max 8 plane.
“The Boeing design requirements for the 737 MAX included the AOA Disagree alert as a standard, standalone feature, in keeping with Boeing’s fundamental design philosophy of retaining commonality with the 737NG. In 2017, within several months after beginning 737 MAX deliveries, engineers at Boeing identified that the 737 MAX display system software did not correctly meet the AOA Disagree alert requirements. The software delivered to Boeing linked the AOA Disagree alert to the AOA indicator, which is an optional feature on the MAX and the NG. Accordingly, the software activated the AOA Disagree alert only if an airline opted for the AOA indicator,” read part of the statement from Boeing.
The optional package that activates the AOA Disagree alert has been purchased by only 20% of airlines, which means the vast majority of Max 8 planes do not have the feature.
The AOA, or the Angle of Attack, is essentially a reading of how far up or down the plane’s nose is tipped. This angle has a bearing on the plane’s ability to maintain lift, as beyond an optimum range, the plane will stall.
The AOA reading is given by two sensors in the Max 8, and the alert would light up if the two sensors reported different readings. With the alert, the pilot would know if the readings are erroneous, and would maybe respond differently.
More pertinently, the Max 8 has a poorly known feature called the Maneuvering Characteristics Augmentation System, which automatically responds to AOA warnings suggesting an impending stall. It is MCAS, activated by erroneous AOA data, that repeatedly pointed the Max 8 nose downwards while attempting to correct for a nonexistent impending stall.
As it were, the crew of the first fatal Max 8 crash, Lion Air 610, seem to have encountered the problem before the fatal incident. In these prior incidences, the crew deactivated the electrical trim system, thus disabling MCAS from sending the plane into a nosedive.
By Matengo Chwanya
Africa Global News Publication
