The Maneuvering Characteristics Augmentation System (MCAS) flight control law was designed and certified for the 737 MAX to enhance the pitch stability of the airplane in a very specific set of unusual flight conditions – so that it feels and flies like other 737s.

MCAS was designed to activate in manual flight, with the airplane's flaps up, at an elevated Angle of Attack (AOA).

Boeing developed an MCAS software update to provide additional layers of protection if the AOA sensors provide erroneous data. Prior to certification, the software was put through hundreds of hours of analysis, laboratory testing, verification in a simulator and numerous test flights, as well as validation during in-flight certification tests with Federal Aviation Administration (FAA) representatives.

The additional layers of protection include:

• The flight control system will now compare inputs from both AOA sensors. If the sensors disagree by 5.5 degrees or more with the flaps retracted, MCAS will not activate. An indicator on the flight deck display will alert the pilots.
• If MCAS is activated in non-normal conditions, it will only provide one input for each elevated AOA event. There are no known or envisioned failure conditions where MCAS will provide multiple inputs.
• MCAS can never command more stabilizer input than can be counteracted by the flight crew pulling back on the column. The pilots will continue to always have the ability to override MCAS and manually control the airplane.

These updates are expected to reduce the crew's workload in non-normal flight situations and prevent erroneous data from causing MCAS activation.

Read the Boeing Statement on AOA Disagree Alert

To earn a Boeing 737 type rating certificate, pilots must complete 21 or more days of instructor-led academics and simulator training. To be certified to fly a 737 MAX, pilots must either complete a 737 MAX specific type-rating course or, if a pilot is already certified to fly the 737NG, they must complete the NG to MAX Differences training.

Prior to the safe return to service of the 737 MAX, Boeing proposed a comprehensive training package with new training requirements that was evaluated and validated by regulators.

The training included a new suite of computer-based training modules, new and updated documentation and simulator training. These instructional materials were designed to provide 737-type rated pilots with an improved understanding of 737 MAX flight control systems, reinforce their technical knowledge of associated flight deck effects and operational procedures, and restore confidence in the 737 MAX.

Maneuvering Characteristics Augmentation System (MCAS) – flight control law implemented on the 737 MAX to improve aircraft handling characteristics and decrease pitch-up tendency at elevated angles of attack.

Angle of Attack (AOA) – the difference between the pitch angle (nose direction) of the airplane and the angle of the oncoming wind.

Angle of Attack Sensor / Vane – hardware on the outside of the airplane that measures and provides angle of attack information to onboard computers; also referred to as an AOA vane.

Angle of Attack Disagree – a software-based information feature that alerts flight crews when data from left and right angle of attack sensors disagree. This can provide pilots insight into air data disagreements and prompts a maintenance logbook entry.

Angle of Attack Indicator – a software-based information feature that provides angle of attack data to the flight crew through the primary flight displays. It is an option that can be selected by customers.

Control law – a set of software that performs flight control function or task

FCOM (Flight Crew Operations Manual Bulletin) – supplementary operations information

FOTB (Flight Operations Technical Bulletin) – supplementary technical information

Speed trim system – a system that uses multiple components to provide additional speed or pitch stability when needed