What role did the MCAS system play in the crashes?

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The MCAS System's Role in the 737 MAX Crashes

The MCAS (Maneuvering Characteristics Augmentation System) flight control software played a role in the two fatal crashes of the Boeing 737 MAX aircraft. This system is designed to prevent a stall by automatically pushing the nose of the aircraft down if it detects erroneous sensor readings indicating a potential stall. In both the Lion Air crash in October and the Ethiopian Airlines crash earlier this month, the MCAS system activated due to faulty sensor data, leading to the aircraft entering unrecoverable flight paths.
Function of the MCAS System

The MCAS system is a new addition to the 737 MAX model, intended to make the aircraft handle similarly to earlier 737 models. Its core function is to automatically adjust the aircraft's pitch downwards, thereby countering the tendency of the larger, more powerful engines on the MAX to cause the nose to pitch up excessively during certain flight conditions, particularly at higher angles of attack. This automatic nose-down input is designed to occur only when the aircraft is at risk of stalling, a condition where the wings lose lift.
Erroneous Sensor Readings and System Activation

In the case of the Lion Air crash, the MCAS system was activated by a single, erroneous reading from an "angle of attack" sensor. This sensor provided data suggesting the aircraft was at a dangerously high angle of attack, which would typically indicate an impending stall. The MCAS software, interpreting this false data as a real threat, repeatedly pushed the aircraft's nose down. This occurred despite the pilots' attempts to correct the aircraft's attitude, as the system continued to receive the same flawed input from the faulty sensor.
Direct Contribution to Fatal Accidents

Investigations have directly implicated the MCAS system's actions in the sequence of events leading to the fatal crashes. The system's repeated and powerful nose-down commands, triggered by what is understood to be faulty sensor data, overwhelmed the pilots' ability to maintain control of the aircraft. Pilots reportedly expressed that they were not adequately informed about the existence or functionality of this new system, which contributed to their difficulties in diagnosing and countering the unexpected flight behavior during critical phases of flight shortly after take-off.

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What role did the MCAS system play in the crashes?

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