Boeing: Incorrect data and anti-stall system played a role in Boeing 737 crashes
Boeing reports that erroneous data from an angle of attack sensor activated the MCAS system during Ethiopian Airlines and Lion Air’s ill-fated flights with the Boeing 737 Max. It is the first time Boeing has acknowledged that the anti-stall software played a role in both crashes.
Boeing CEO Dennis Muilenburg said in a video message that full details of what happened in both accidents are yet to follow in final reports, but it is clear that the MCAS system was activated in response to erroneous data from an angle of attack sensor. He apologizes to the 346 people who died in the crashes in Indonesia and Ethiopia.
Earlier there were reports that the system, which is designed to automatically push the nose of the aircraft down to avoid a stall situation, was reactivated up to four times. Muilenburg said nothing more about this. He does not yet address the question of whether the pilots can also be blamed. Muilenburg indicates that a chain of successive mistakes eventually led to the crashes. For now, it remains unclear whether the system reactivated itself or whether the pilots turned it back on after a previous shutdown.
Muilenburg made his comments in response to the first non-final report released by the Ethiopian transport minister on Thursday. Minister Dagmawit Moges reported that the pilots acted in accordance with all procedures prescribed by Boeing, but were nevertheless unable to control the aircraft. Moges said there were repeated commands pushing down the nose of the plane and called on Boeing to investigate the flight control system in question. She gave few details and made no specific recriminations.
The Boeing CEO states that an update that should make the MCAS system more secure is almost ready. He expects the new software to be implemented in the worldwide Boeing 737 Max fleet and certified in the coming weeks. According to him, this update will “eliminate the possibility of an accidental MCAS activation and prevent another MCAS-related accident from ever happening again.” He also talks about additional training and educational materials for pilots of the new Boeing 737 type. With the software changes, the 737 Max is, according to Muilenburg, ‘one of the safest aircraft ever’.
On the Boeing 737 Max, two angle of attack sensors on either side of the nose of the aircraft measure the incoming horizontal airflow. Based on that data, the angle of the aircraft in relation to the airflow can be determined. If that data is incorrect, the system can get the impression that the device is leaning too much backwards, which could theoretically lead to a dangerous stall situation. MCAS is designed to automatically push the nose down in such a case and prevent a device from falling from the sky due to lack of lift. In both crashes, the pilots were unable to counteract the operation of the system. Boeing’s update ensures that MCAS is controlled based on both angle of attack sensors instead of a single one and makes it easier to disable the system.
CNN reports that US NTSB aeronautics investigators are also now investigating two US companies involved in the manufacture and maintenance of the angle of attack sensors used in the ill-fated Lion Air flight last October. A refurbished angle of attack sensor would have been used on that flight. It is not yet clear to what extent this played a role in the crash. The Lion Air flight killed 189 people; 157 people died in the plane crash in Ethiopia.
Update, 10:07 PM: Boeing reports that it has found a second software problem. The company provides few details about it, but does say that this issue is not related to the MCAS system. A fix for this second issue will be implemented with the software update mentioned above.