Boeing and the FAA decided that the AOA display and an AOA disagree light , which signals if the sensors give different readings , were not critical features for safe operation . Boeing charged extra for the addition of the AoA indicator to the primary display . In November 2017 , Boeing engineers discovered that the standard AoA disagree light can not independently function without the optional AoA indicator software , affecting 80 % of the global fleet which had not ordered the option . The software remedy was scheduled to coincide with the roll out of the elongated 737 MAX 10 in 2020 , only to be accelerated by the Lion Air accident . Furthermore , the problem had not been disclosed to the FAA until 13 months after the fact . Although it is unclear whether the indicator could have changed the outcome for the ill-fated flights , American Airlines said the disagree indicator provided the assurance in continued operations of the airplane . " As it turned out , that was n't true . " Boeing CEO Dennis Muilenburg has stated that there was " no surprise , or gap , or unknown here or something that somehow slipped through a certification process . " On April 29 , 2019 he stated the design of the aircraft was not flawed and reiterated that it was designed per Boeing 's standards . In a May 29 interview with CBS , Boeing admitted that it had botched the software implementation and lamented the poor communications
Lion Air accident
Lion Air Flight 610
Maneuvering Characteristics Augmentation System