Cause of Ethiopian crash
I am not a pilot or aviation expert. My interest is because my late father was a research engineer at the Royal Aircraft Research Establishment in Farnborough, and we used to discuss air crashes and their causes. I continue to be interested. Sifting through the information to date, and the excellent journalism by the Seattle Times, this is my layman's take on the likely cause of Ethopian plane crash. Am I close?
Why the Boeing 737 Max 8 crashed in Ethiopia in March 2019
The Boeing 737 Max 8 has larger engines mounted further forward than on previous versions. This causes the possibility of a stall on take-off, as it can make the Angle of Attack (AOA) too steep. To compensate, Boeing introduced a "small" software fix (the MCAS) to automatically adjust this, pointing the plane nose down. It was considered so small a fix that it was not included in initial documentation for the updated jet or in information for pilot retraining.
Meanwhile the US FAA (Federal Aviation Administration), citing staff and budget shortages, had earlier delegated some aspects of safety assurance for the plane, back to Boeing, making it self regulating in some areas, including the MCAS fix. The FAA also seems to have been keen to help Boeing get the new plane certified and available for sale as it was facing stiff competition from the Airbus.
During testing it emerged that the AOA adjustment made by the MCAS software was insufficient and so this was increased by a factor of 4, however this was not updated in the safety documents (according to unnamed informants). In addition the MCAS software resets itself from scratch every time it is activated. All this means that if there is a faulty reading from one of the external AOAs, the MCAS will continuously reset the nose of the plane downwards, as if it was doing it for the first time each time.
In the safety documentation, an AOA sensor failure is classified as a serious hazard but not as catastrophic which would have caused a delay in certification. Some experts say that a single point of failure like this is catastrophic while others say an experienced pilot should be able to handle it.
This AOA sensor failure is what seems to have happened with the Lion air fatal crash of a Boeing 737 max 8 in Indonesia last October. At that time the pilots did not know about the MCAS fix. The existence of the MCAS came to light after this and its existence was then included in pilots retraining. The official report on the Lion Air disaster is not due out until later this year. Boeing has been working on a fix since then but says it was delayed by the public sector shut down in the US earlier this year and it is now due in May.
Initial indications are that a similar accident occurred with last week's fatal Boeing crash in Ethopia.
Last edited by Nightingale14; 18th Mar 2019 at 13:42.
Reason: grammar error