A statement released by Boeing shows that the airframer was aware of a software issue with MCAS on the Boeing 737 Max in 2017 but chose not to act.
Manoeuvring Characteristics Augmentation System (MCAS) has been implicated in two fatal Boeing 737 Max 8 crashes a Lion Air Crash in 2018 which killed 189 people and more recently an Ethiopian Airways crash in 2019 which killed 157 people.
In the statement, Boeing says that “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.”
The statement mentions the Angle of Attack (AoA) Disagree alert which was being sold as an option on Boeing 737 Max aircraft, the alert informs pilots if there is a discrepancy between the angle of attack sensors.
Initial reports from both crashes show that the AoA sensors were providing incorrect data and this alert could have informed the pilots of both aircraft that a sensor was malfunctioning. As a result of the faulty the sensor the aircraft believed the AoA was too high and the MCAS system tried to push the nose down.
As a result of the two accidents, all 737 Max 8 aircraft are currently grounded and Boeing says that it is issuing a software update that will, amongst other things, make the disagree alert active on all aircraft, not just those where the airline chose it as an option.
For Boeing, questions will now need to be asked as top why their engineers didnt act in 2017 when a review concluded that it did not need to act immediately as “the existing functionality was acceptable until the alert and the indicator could be delinked in the next planned display system software update “
The company added that: “Senior company leadership was not involved in the review and first became aware of this issue in the aftermath of the Lion Air accident.”
The revelations about this issue are bound to further damage the reputation of Boeing and the Boeing 737 which is the top-selling aircraft in aviation history. It remains to be seen how much damage this will do to future sales of the latest Max variant.
The issue is costing airlines millions by having to lease in aircraft or in some cases, bring older aircraft back from retirement to cover their grounded aircraft. No date yet has been identified for when the 737 Max 8 fleet will be cleared to fly again.
