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 – so that it feels and
flies like other 737s.
MCAS is designed to activate in manual flight, with the airplane’s flaps up, at an elevated Angle
of Attack (AOA).
Boeing has developed an MCAS software update to provide additional layers of protection if the
AOA sensors provide erroneous data. The software was put through hundreds of hours of
analysis, laboratory testing, verification in a simulator and two test flights, including an in-flight certification test with Federal Aviation Administration (FAA) representatives on board as
The additional layers of protection include:
• 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 reduce the crew’s workload in non-normal flight situations and prevents
erroneous data from causing MCAS activation.
We continue to work with the FAA and other regulatory agencies on the certification of the
To earn a Boeing 737 type rating, pilots must complete 21 or more days of instructor-led academics and simulator training. Differences training between the NG and MAX includes computer-based training (CBT) and manual review.
Boeing has created updated CBT to accompany the software update. Once approved, it will be accessible to all 737 MAX pilots. This course is designed to provide 737 type-rated pilots with an enhanced understanding of the 737 MAX Speed Trim System, including the MCAS function, associated existing crew procedures and related software changes.
Pilots will also be required to review:
• Flight Crew Operations Manual Bulletin
• Updated Speed Trim Fail Non-Normal Checklist
• Revised Quick Reference Handbook
737 MAX Flight Deck Displays Overview
All primary flight information required to safely and efficiently operate the 737 MAX is included
on the baseline primary flight display. Crew procedures and training for safe and efficient
operation of the airplane are focused around airplane roll and pitch attitude, altitude, heading
and vertical speed, all of which are integrated on the primary flight display. All 737 MAX
airplanes display this data in a way that is consistent with pilot training and the fundamental
instrument scan pattern that pilots are trained to use.
The AOA (angle of attack) indicator provides supplementary information to the flight crew. The
AOA disagree alert provides additional context for understanding the possible cause of air
speed and altitude differences between the pilot’s and first officer’s displays. Information for
these features is provided by the AOA sensors.
There are no pilot actions or procedures during flight which require knowledge of angle of
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 airline 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
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