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Old 20th Nov 2018, 11:42
  #1418 (permalink)  
Join Date: Jun 2006
Location: Brisbane
Posts: 10
Originally Posted by lakedude View Post
I am not your knowledgeable authority figure but I have read the entire thread from the beginning and will be happy to summarize.

Before November 6th there was not much in the way of consensus as to a possible cause. Unreliable Air Speed (UAS) possibly due to the covers being left on the speed sensors was the talk of the day.

On November 6th Boeing issued a statement that changed the focus to the Angle Of Attack (AOA) sensor. Specifically that bad data from an AOA sensor could cause uncommanded nose down trim on the stabilizer (horizontal part of the tail).

Link to November 6th discussion: Indonesian aircraft missing off Jakarta

At some point Boeing disclosed the existence of a new feature named MCAS that was evidently not previously disclosed to pilots. MCAS is an anti-stall feature that was not required (or implemented) on older versions of the 737. When working properly with good AOA data MCAS trims the stabilizer to lower the plane's nose in an attempt to mitigate a stall. MCAS could have been a lifesaver under different circumstances, however...

MCAS along with faulty AOA data seems to be prevailing theory as to what might have been at least a contributing factor in the crash. The idea being that bad AOA data fed to MCAS caused the plane to be trimmed more and more nose down, ultimately leading to a crash.

Disclaimer: This is my interpretation of the speculation posted here by others. I could easily have goofed something up.
That’s one way of surmising.

But the simple fact is that at this point, PPRuNe readers have no knowledge of what happened outside of FR24 data and what has been released in the media.

The only thing that has been released in the media is the Boeing AD regarding MCAS. It hasn’t been concluded that MCAS was the primary cause of the accident, however, given the publication of the AD, it has been the main subject of conjecture on this forum as a “contributing factor” (thank you lakedude).

Most accidents prove to have several “contributing factors”, and I’m sure this will be one of them.

I would suggest that the eventual analysis will include other contributing factors, including the quality of maintenance (given the evidence of the previous 3 sectors), and the quality of training (given that this event should have been survivable if indeed it was only an air data problem).

I don’t work for Boeing, but given the track record of this operator, I am really surprised at the outburst against Boeing on this thread. Boeing is not in charge of maintenance standards or training standards at customer airlines. If you want to buy a ticket to fly on a low cost airline, you carry a risk. Until the planes start crashing, low cost operators will continue to reduce standards. Eventually they will reach a point where the planes start crashing, and tragically, people will die. I will leave it to the community to decide when that point has been reached.

Last edited by Derfred; 20th Nov 2018 at 12:24.
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