The Ethiopian Airlines accident on 10th March 2019 was the 2nd B-737 Max accident in 4 months. This created a public outcry about the safety of Boeing 737 around the world and given the fact that Boeing had not been forthcoming in its disclosure of the new software, MCAS.All countries flying the B-737 had to ground the aircrafts flying in their airspace and the last but not the least the FAA very reluctantly followed suit.
Every one tried to draw similarities between the accidents stating that the flight profile was similar and that both the aircrafts nose dived shortly after takeoff. For the first time in the history of aviation that the entire fleet around the world had been grounded on the basis of public perception and without any evidence. This also showed the lack of trust that the regulators of all the countries had with FAA and Boeing.
Data can be misrepresented if graphs are not plotted using the same variables or set out of sequence.
The world is finding the following common:
- Both aircraft were the B-737 Max series
- Both aircrafts crashed shortly after take off.
- Both aircrafts initial Flightradar24 data shows a pronounced dip. Where as MCAS seems to be the reason for that dip in the case of the Lion Air accident, it is now assumed that the same MCAS would be the cause of the Ethiopian Air accident.
If the two flight data were to be plotted separately, they would appear no where similar.
The Lion Air flight data graph above shows a pronounced dip before a sharp climb. The altitude line is also serrated and not smooth. This is due to the fact that the stick shaker was activated from the moment the aircraft got airborne. The stick shaker is a device which continuously moves the pilot’s control column or vibrates it before the aircraft stalls and looses height. The MCAS trims the nose down in bursts of stabaliser trim.
The Ethiopian Air flight data graph above shows a shallow climb without any pronounced dip. The line is also smooth as against the serrated climb line of the Lion Air accident.
As highlighted in my previous blog, the Ethiopian Air accident does not give obvious indications of MCAS as the primary reason of the accident.
The cause most probably lies in the takeoff segment where the aircraft apparently initiates a low speed lift off (rotation) and thereafter continues to accelerate down the runway but fails to gain much height. Thereafter the flight path is unstable with fluctuating vertical speed up and down. Eyewitness report debris falling and smoke from the rear of the aircraft.
There could be a structural failure or flight control failure very early in flight.