Were the Ethiopian Airlines Pilots Aware of the MCAS and How to Disable It?
The tragic loss of lives in the Ethiopian Airlines flight 302 in March 2019 brought to light several critical discussions surrounding the safety and operation of modern aircraft. One of the key points of debate was whether the pilots were aware of the Maneuvering Characteristics Augmentation System (MCAS) and how to disable it in case of malfunction.
Background: The MCAS System
The Maneuvering Characteristics Augmentation System (MCAS) was introduced to address the safety concerns that emerged from the performance of the 737 Max aircraft during extreme maneuvers. Despite its initial purpose, the MCAS system became a focus of scrutiny following the multiple accidents involving the aircraft, including the Ethiopian Airlines incident.
The FAA Emergency Airworthiness Directive AD 2018-23-51
Before the tragic flight, the Federal Aviation Administration (FAA) published an emergency airworthiness directive, AD 2018-23-51, which acknowledged the presence of the MCAS system. This directive, though, didn't provide detailed insights into the system's operation or potential malfunctions. Instead, it referred pilots to a general checklist for handling a runaway stabilizer, which is a similar situation to a malfunctioning MCAS.
The MCAS System and Its Relevance to the Ethiopian Incident
The MCAS system is designed to prevent stall conditions by automatically lowering the nose of the aircraft. However, it can also apply large and subtle nose-down trim modifications if faulty Angle of Attack (AoA) data is provided or blamed. In the case of the Ethiopian flight, the manual trim wheels were ineffective in reversing the MCAS-applied trim, indicating a significant limitation in pilot control.
Actions by the Pilots
During the flight, the pilots took several actions to attempt to regain control of the aircraft. They disabled the electric trim system, which is the only method to completely prevent the MCAS from applying nose-down trim modifications. This shows that they were well aware of the checklist item and its importance in controlling the aircraft's behavior.
However, the pilots also failed to disengage the autothrottle, which is another recommended action in the runaway stabilizer checklist. This oversight could have had significant implications, as the autothrottle is designed to maintain optimal thrust and speed, and its disengagement might have helped in managing the aircraft's performance.
Boeing's Role and Testing
The discussions about the Ethiopian Airlines incident have not stopped at addressing the pilots' actions. Boeing, the manufacturer of the 737 Max, has been under scrutiny for not thoroughly testing the effect of their recommended actions. The company pointed out that faulty AoA data could trigger a runaway stab trim situation but downplayed other potential effects and indications that could have helped in understanding the full scope of the MCAS system.
Conclusion and Lessons Learned
The tragedy of the Ethiopian Airlines flight 302 highlights the critical importance of comprehensive safety protocols and thorough testing of systems in modern aviation. Whether the pilots were fully aware of the MCAS and how to disable it effectively remains a point of debate. However, it is clear that the system's design and the lack of clear, effective guidance for pilots contributed significantly to the challenges faced during the flight.
As the aviation industry continues to evolve, it is imperative that manufacturers, regulatory bodies, and pilots work together to ensure that all safety systems are thoroughly tested, well-documented, and effectively communicated. The lessons from this incident must not be forgotten as the industry moves forward.