The accident investigation agencies disagree about what factors led to the 2019 crash of Ethiopian Airlines flight 302. //

The NTSB and the EAIB have differing opinions as to what caused the failure of MCAS and the subsequent Ethiopian crash.

“According to the EAIB’s final report, electrical problems that existed since the time of the accident airplane’s production caused the left angle-of-attack sensor heater to fail, which resulted in the AOA sensor providing erroneous values that caused the MCAS to pitch the nose of the airplane downward,” resulting in the crash, the NTSB report reads.

The NTSB report states that it found no evidence to support the suggestion of an electrical problem resulting in a nose-high attitude and failure of the MCAS, but suggests the faulty reading was “caused by the separation of the AOA sensor vane due to impact with a foreign object, which was most likely a bird.” //

There was no mention of MCAS issues in the pilot manuals when the Max entered service in 2017.

After the first crash, MCAS manuals were made available to 737 Max crews. Boeing stressed that MCAS was designed for better aircraft handling, not as a stall prevention tool.

After the second crash, the world’s 737 Max fleet was grounded for the better part of two years while changes were made to the MCAS software and training protocols were developed. The aircraft returned to service in November 2020.

The NTSB noted the EAIB issued its final report without giving the NTSB the opportunity to review new information incorporated since the NTSB’s last review and provide comments ahead of the report’s issuance, as stipulated by the International Civil Aviation Organization’s Annex 13.

The NTSB stated it had provided the EAIB with evidence supporting the bird contamination theory, but that evidence was not included in the EAIB final report.

The NTSB also noted the EAIB’s finding about the lack of MCAS documentation for flight crews was misleading since Boeing had provided the information to all 737 MAX operators four months before the Ethiopian Airlines crash.