What does MCAS do?

MCAS, or Maneuvering Characteristics Augmentation System, provides consistent airplane handling characteristics in a very specific set of unusual flight conditions. MCAS now contains multiple enhanced protections:

    • Measurements from two Angle of Attack (AOA) sensors will be compared.
    • Each sensor will submit its own data to the airplane’s flight control computer.
    • MCAS will only be activated if both sensors agree.
    • MCAS will only be activated once.
    • MCAS will never override the pilot’s ability to control the airplane using the control column alone.

What else should I know about MCAS?

Why do newer 737s need MCAS?
U.S. Federal Aviation Administration (FAA) regulations require that all commercial jetliners have smooth handling characteristics in all flight conditions. This includes rare instances where the nose of the airplane is unusually high, such as when it is climbing aggressively or performing excessively tight turns with high bank angles.

When does MCAS activate?
MCAS was designed to activate only when all three of the following conditions occur at the same time:

    1. The pilot is flying the airplane manually.
    2. The airplane nose approaches a higher-than-usual angle.
    3. The pilot has the wing flaps up.

How did MCAS initially work?
Prior to being enhanced, MCAS relied on information from a single Angle of Attack (AOA) sensor to monitor the angle of the airplane. In the two accidents, a single AOA sensor gave incorrect information to MCAS, which caused it to activate. In both cases, MCAS engaged repeatedly when the sensor continued to incorrectly report a high AOA.