Investigation Summary
The accident was the second fatal crash of a Boeing 737 MAX in less than five months. The investigation centered on the MCAS, a flight control law designed to improve handling at high angles of attack. In this event, a failure of the left AOA sensor—attributed by the EAIB to electrical faults and by the NTSB to a bird strike—caused MCAS to activate erroneously. The crew initially followed the 'Airspeed Unreliable' and 'Runaway Stabilizer' procedures, including cutting power to the electric trim. However, due to high aerodynamic loads on the stabilizer and high airspeed (resulting from the engines remaining at takeoff thrust), they were unable to manually trim the aircraft. When they reactivated the electric trim to assist, MCAS triggered again, forcing the aircraft into an unrecoverable dive.
Final Conclusions
The EAIB concluded the probable cause was the erroneous AOA sensor data triggering MCAS, which the crew could not overcome due to the system's design and lack of specific training. The NTSB, while agreeing on the role of MCAS, emphasized human factors and the crew's failure to manage thrust, which exacerbated the control difficulties.
Video Analysis
The Real Reason Boeing 737 Max Crashed — An analysis of the Ethiopian Airlines Flight 302 accident and the technical failures of the MCAS system.
Watch on YouTube ↗If playback is blocked, the owner has disabled embedding — use the link above.
Systems & Failure Modes
MCAS
Maneuvering Characteristics Augmentation System; designed to provide pitch-down input to improve handling at high AOA.
AOA Sensor
Angle of Attack sensor; measures the angle between the wing's chord line and the oncoming airflow.
STAB TRIM CUTOUT
Switches that disconnect power to the horizontal stabilizer trim motor.
Interesting Facts
- 01The aircraft was nearly brand new, delivered to Ethiopian Airlines in October 2018.
- 02The left AOA sensor failed almost immediately after takeoff, reaching a value of 74.5 degrees.
- 03The aircraft reached speeds exceeding 400 knots during the final descent.
- 04This accident led to the global grounding of the Boeing 737 MAX fleet.
- 05The NTSB and EAIB disagreed on the initial cause of the AOA sensor failure (Bird strike vs. Electrical fault).
Safety Actions & Advisories
Global Fleet Grounding
The Boeing 737 MAX fleet was grounded worldwide for nearly two years while flight control software was redesigned.
MCAS Redesign
Boeing updated MCAS to compare inputs from both AOA sensors and limit the system's authority so it cannot override pilot input.
Enhanced Pilot Training
Mandatory simulator training for 737 MAX pilots focusing on MCAS logic and stabilizer trim malfunctions.