The Maneuvering Characteristics Augmentation System ( MCAS ) is a flight control software system developed for the Boeing 737 MAX to provide handling qualities similar to the Boeing 737 NG , especially in low-speed and high angle of attack ( AoA ) flight . It lowers the nose without pilot action when it determines the aircraft is too nose-high , based on input from airspeed , altitude and angle of attack sensors . However , it is susceptible to erroneous activation , as evidenced in the deadly crashes of Lion Air Flight 610 and Ethiopian Airlines Flight 302 . The 737 MAX is indefinitely grounded until regulators decide the aircraft is airworthy , pending software and instrumentation updates and revisions to information for flight crews . They may also be required to undergo MCAS training sessions in flight simulators
Ethiopian Airlines Flight 302
Ethiopian Airlines Flight 302
Boeing 737 MAX