What happened
On March 10, 2019, an Ethiopian Airlines B737-MAX 8, registered as ET-AVJ, was involved in a fatal accident during a flight operated by the airline. The aircraft was operating under standard flight conditions when a critical failure occurred involving the flight control systems. The sequence of events led to an uncontrollable flight profile, resulting in the loss of the aircraft and all occupants.
The investigation
The investigation, conducted by the Ethiopian Airplane Accident Investigation Bureau (EAIB), focused on the aircraft's automated flight control systems, specifically the Maneuvering Characteristics Augmentation System (MCAS). Investigators examined the flight data recorder (FDR) and cockpit voice recorder (CVR) to reconstruct the flight path and crew actions. The probe specifically analyzed the inputs from the Angle of Attack (AOA) sensors and how the Enhanced Digital Flight Control System (EDFCS) responded to erroneous data. The investigation also reviewed the maintenance history of the engines and the integrity of the stabilizer trim systems.
Findings
Technical analysis established that the accident was driven by erroneous data from a single AOA sensor, which triggered the MCAS. In the aircraft's original design, the MCAS relied on a single sensor input, allowing a faulty reading to initiate repeated nose-down commands to the horizontal stabilizer. This created a runaway stabilizer condition that was difficult for the crew to counteract. The investigation found that the system's reliance on a single point of failure allowed the automated system to repeatedly command pitch-down movements, significantly complicating the crew's ability to maintain control of the aircraft.