And Another Thing …
On 27 December 2022, the National Transportation Safety Board (NTSB) took the unusual step of publishing comments it had previously provided to the Ethiopian Aircraft Investigation Bureau (EAIB) regarding the latter agency’s final report on the 10 March 2019 loss of a Boeing 737 MAX-8 aircraft operating as Ethiopian Airlines Flight 302. The NTSB set forth that the EAIB had “failed to include the NTSB’s comments in its final report on its investigation.”
In accordance with the provisions of the International Civil Aviation Organization (ICAO) Annex 13, countries participating in the investigation of a given accident or incident are afforded opportunity to review draft reports and provide comments pursuant to such to the investigating authority. In the event the investigating authority disagrees with the comments or declines to integrate them into the accident report, participating countries are entitled to request that their comments be appended to the final report.
According to the NTSB, the EAIB’s draft report failed to include salient input from the NTSB, including numerous assessments of the accident’s probable causes.
On 24 January 2023, the NTSB released additional comments pertaining to the Ethiopian Aircraft Investigation Bureau’s final report on the loss of Ethiopian Airlines Flight 302.
The new comments—issued to the attention of the EAIB’s investigator-in-charge—reasserted the NTSB’s concerns about several of the findings in the EAIB’s final accident report, and reiterated the board’s conclusion that EAIB investigators failed to comprehensively assess the accident’s human performance aspects.
Notwithstanding its agreement with the EAIB’s indictment of the 737 MAX’s Maneuvering Characteristics Augmentation System (MCAS), the NTSB argued the EAIB’s final report contains findings not supported by empirical evidence. Principal among these are the EAIB’s attribution of erroneous Angle of Attack (AOA) readings to anomalies peculiar to the 737 MAX’s electrical system.
In its final report, the EAIB posited electrical anomalies endemic to all 737 MAX family jets had precipitated failure of the heating element within the downed aircraft’s AOA sensor, thereby occasioning erroneous AOA values which, in turn, compelled the MCAS to command an unrecoverable series of nose-down pitching moments.
The NTSB, contrary to the EAIB’s finding, determined the erroneous AOA values had been caused by separation of the AOA sensor vane from the aircraft following impact with a foreign object—most likely a bird. During the Ethiopian Airlines Flight 302 accident investigation, the NTSB presented evidence supporting bird-strike—evidence the EAIB omitted from its final report.
The NTSB also contradicted the EAIB’s contention that Boeing had failed to provide Ethiopian Airlines pilots and training personnel adequate MCAS documentation. The NTSB characterized the EAIB’s conclusion to the contrary as misleading, and pointed out that Boeing had provided data and documentation germane to the MCAS to all 737 MAX operators four months prior to the downing of Ethiopian Airlines Flight 302.
A full transcript of the NTSB’s comments pertaining to the EAIB’s final report on the loss of Ethiopian Airlines Flight 302 is available online.
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