Quote – French air accident investigation agency BEA said on Tuesday the flight data recorder in the Ethiopian crash that killed 157 people showed “clear similarities” to the Lion Air disaster. Since the Lion Air crash, Boeing has been pursuing a software upgrade to change how much authority is given to the Manoeuvring Characteristics Augmentation System, or MCAS, a new anti-stall system developed for the 737 MAX. – Unqoute.
Quote – The captain fought to climb, but the computer, still incorrectly sensing a stall, continued to push the nose down using the plane’s trim system. Normally, trim adjusts an aircraft’s control surfaces to ensure it flies straight and level – Unquote
Analysis from publicly available news & articles, sources and references at the end of article.
Sequence of events:
- 737 Max has heavier engines which are mounted higher than other planes
- This may cause stall at lower speeds by pushing nose up
- To correct this a mechanical sensor is kept at the front of the plane to detect air flowing in parallel or at an angle known as angle of attack
- This sensor is connected to MCAS automation software based system which controls TRIM electro-mechanical system which keeps aircraft level and straight
- MCAS typically pushes nose down due to stall created by higher nose level as above
- In this case the sensor seemed to be faulty so MCAS wrongly took over
- Pilots didn’t know how to disengage the MCAS. They had to cut power to the motor that pushes nose down
- Another pilot who was in one of the same flights earlier could disengage MCAS by stopping the motor for a similar problem by cutting power to motor pushing nose down
Sources & references below:
https://en.wikipedia.org/wiki/Automation
https://airlinerwatch.com/boeing-737-max-8-design-or-software-problem/