The Maneuvering Characteristics Augmentation System (MCAS) is a flight control system designed by Boeing to help prevent the Boeing 737 MAX from stalling. It automatically adjusts the angle of the aircraft's horizontal stabilizer to lower the nose if it senses the plane is flying at too high an angle of attack.

The system was developed in response to the Federal Aviation Administration's (FAA) concerns about the 737 MAX's handling characteristics. The FAA had found that the plane was prone to pitching up unexpectedly, which could lead to a loss of control.

MCAS is designed to activate when the plane's sensors detect that it is flying at a high angle of attack. When MCAS is activated, it will automatically move the horizontal stabilizer to lower the plane's nose. This will reduce the angle of attack and help to prevent the plane from stalling.

The system is designed to be fail-safe, meaning that it will not activate unless it receives data from multiple sensors. If one sensor fails, MCAS will not be able to activate.

The FAA has approved the use of MCAS on the 737 MAX, but the system has been implicated in two fatal crashes. In 2018, a Lion Air 737 MAX crashed in Indonesia, killing all 189 people on board. In 2019, an Ethiopian Airlines 737 MAX crashed in Ethiopia, killing all 157 people on board.

Following the two crashes, the FAA grounded all 737 MAX aircraft in the United States. The FAA has since lifted the grounding order, but the agency has required Boeing to make several changes to the MCAS system.

The future of the 737 MAX is still uncertain. Some airlines have already canceled their orders for the plane, and others are considering doing so. Boeing has said that it is confident that the 737 MAX is safe and that it will continue to sell the plane.