PPRuNe Forums - View Single Post - MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
Old 25th Aug 2019, 22:08
  #2038 (permalink)  
Join Date: Dec 2018
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I realized how confusing the situation would have been for the Ethiopian captain after working on my comment comparing the differences between the pressure altitudes computed on the left side and the right side.

The broken AOA indicator messed up the computed pressure altitude on the captain side so severely that it was showing the aircraft much lower than it actually was, more than 1000 feet lower as the speed increased, reaching almost 3000 feet difference during the final dive. At some point after the MCAS activation the aircraft was slightly climbing, but the captain pressure altitude was showing the aircraft as failing to climb, despite the increasing speed. Also the indicated airspeed was lower on the left side than on the right side by up to 25 knots.

So overall the instruments were presenting to the captain a situation much worse than it actually was. It's not the same thing if you are at 1500 feet, you lose 250 feet of altitude, and then the aircraft slowly starts climbing, compared with what the captain was actually seeing: being at around 950 feet and losing 450 feet of altitude, then the aircraft not climbing at all, despite the increasing speed.

With that in mind, even ignoring other factors, it becomes more understandable why the captain didn't reduce thrust. And I think determining quickly which side had the unreliable airspeed and altitude information, and using the information from the other side, is one thing that could have prevented the accident.

Last edited by MemberBerry; 25th Aug 2019 at 22:32.
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