Overriding the 737 MAX software

Boeing is to add redundancy and other limits to its 737 MAX’s fly-by-wire software, so it is less likely to command nose-dives to counter aerodynamic stall when no such danger exists

Boeing 737 MAX: Manoeuvring Characteristics Augmentation System (MCAS) – anti-stall system uses data from angle-of-attack sensor to detect if plane is climbing too steeply
and risking stall

AIR FLOW

Horizontal stabilizer: Controls up-and-down pitch of nose

Angle of attack (AOA)

Hinge
Jackscrew actuator: Moves angle of stabilizer up or down

High angle of attack: MCAS changes angle of stabilizer, pushing tail up.
As a result, aircraft nose goes down

1 Trim switches: Temporary solution – pilot can use stabilizer trim switches to reverse downward trim

2 Jackscrew control: Flip twin switches on central console to disable electric control of jackscrew for rest of flight

3 Stabilizer trim wheels: Spin wheels to manually pull stabilizer back into correct position

Yoke

Stick-shaker: Vibrates yoke if approaching stall

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Sources: Boeing 737 Max fleet bulletin TBC-19, The AIr Current, Flight Global

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