The Maneuvering Characteristics Augmentation System (MCAS) is a subsystem of the Boeing 737 MAX flight control system which attempts to mimic pitching behavior similar to the Boeing 737 NG, especially in low-speed and high angle of attack (AoA) flight. When it detects that the aircraft is in imminent danger of entering an aerodynamic stall, based on input from airspeed, altitude and angle of attack sensors, it adjusts the horizontal stabilizer trim to bring the aircraft nose down.