PPRuNe Forums - View Single Post - Ethiopian airliner down in Africa
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Old 4th Apr 2019, 15:58
  #3113 (permalink)  
Join Date: Feb 2011
Location: Grand Turk
Age: 57
Posts: 66
Originally Posted by gmx View Post
You might have to explain that further. The LionAir crash FDR clearly shows short bursts of uncommanded nose-down trim (from MCAS), each one counteracted by PF-commanded nose-up electric trim, maintaining level flight at 5000 feet for roughly six minutes. The uncommanded nose-down trim is never coincident with the PF's nose-up electric trim. They are clearly interleaved, which is exactly the MCAS behaviour described by the updated advice.

The erroneous AoA / AP disconnect / MCAS response chain may have manifested differently on the EA flight, but we'll have to wait for the FDR / CVR data in the report to know one way or the other.
Quite simply the LionAir data does not establish that it is possible to win the battle between Electric Trim and MCAS (particularly if time is of the essence). With combined opposing authority it may only have have a marginal effect on trim. While that may be sufficient to maintain control if the trim is close to optimum it may not be enough if the trim is already way off. Like you say, the data on Ethiopian has not been released yet. However, the published information on the LionAir incidents is not sufficient to draw firm conclusions. I will concede that in the LionAir incident it would appear to be the case that the situation could have been resolved by acting sooner; as in the previous flight. It is not clear that the same is true in the Ethiopian accident. It also may be of some importance that the situation developed at a later stage in the previous LionAir flight. Despite reading most of what is available, I still have more questions than there are answers. In the LionAir incident (crash) stick-shaker started at the beginning of the take-off roll... it is a stage that puts particular stress on the crew to properly interpret and react.
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