Old 14th Mar 2019, 21:40
  #188 (permalink)  
fdr
 
Join Date: Jun 2001
Posts: 547
CB737;

the debris field in Addis indicates that on the day, prior knowledge didn't alter the outcome effectively. The individual may be easily blamed post hoc, that is the way of the world, however, in this case one can assume that the flight crew had a vested interest in having a boring day and not making headlines, yet it didn't end up that way. The fault that occurs with the MCAS has defeated two crews to date. ET's FDR, CVR and debris evidence will show whether the crew got the stab cutout switches in the sequence. Centaurus' comments and the associated thread on aerodynamic load reduction on the stab is quite possibly the missing piece in both of these events.

The certification requirement doesn't provide a guarantee of elevator authority being able to always offset an incorrect stabiliser setting. 25.255 and 25.665 cover the trim case in general, however the setup for show compliance is not the type of event that occurred. 25.672 covers stability augmentation system requirements and is probably going to get an airing in court in the near future, each paragraph is going to be topical. Boeing, Airbus, Cessna and various other aircraft builders have come across events where the stab trim has compromised controllability. Boeing, FAA SEA ACO/TAD have competent people in their programs, finding latent failures before an event is hard, it is much easier afterwards, and ET's loss speaks loudly that more is to be learnt here in order to reliably defend operation.


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