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MCAS Deconstructed by PPRUNE Members??!!

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MCAS Deconstructed by PPRUNE Members??!!

Old 2nd May 2019, 04:44
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MCAS Deconstructed by PPRUNE Members??!!

This thread might belong in Tech, but given the significance of MCAS and Boeing’s future I decided this was the place for it. Apologies in advance if I chose poorly…


I realized earlier today that I have a problem.

Over the past month and a half I’ve read almost 5000 posts on a thread on some rumor blog/forum, and much to my chagrin I’d actually posted on the site…

And yet, despite that effort, insight, shared knowledge and my own experience I am no closer to understanding the fundamental details behind what happened and why than I was when I started. This is primarily due to the fact that MCAS is (right now) an enigma. Various sources have the certification requirements to be no less than three that MCAS was intended to insure compliance with.

I haven’t seen anyone work out step by step what MCAS does, and how it does it. Sure, we all know that MCAS will trigger at a threshold AOA and run for 9.26 seconds if the AOA doesn’t drop into an acceptable range. But after that the list of questions is almost endless.

I want to challenge PPRUNE and our vast technical resources here (and those (including me) who have spent the better part of four weeks arguing over Boeing vs. four dead pilots...) to parse MCAS to a level that no one else will likely achieve. Why was it needed, what problem was it intended to solve, why was it chosen over other more technically robust solutions, why is it a “dumb” system that does not adapt in any way, why did Boeing use an actual control system when (they say??) it was just a control force augmentation system??

Think about it- if we are to properly judge the remediation and return of service of the MAX then it is up to us to have an intimate understanding of the systems the fix is intended to remediate.

To do this we need to start at the beginning:

Is there anyone out there who has verified source material that states explicitly why MCAS was created?? (After 5000 posts I am no better informed now than I was when I started…)

Let’s start there- what exactly was MCAS designed to deal with. What FAR, what aerodynamic or control feel problem… Please provide any original source material you have, no matter whether or not it is probative.

Let’s ID the problem first. Then we can look at the solution and whether or not it was a good one.

Thank you in advance for your entertainment of this quest. I should live in the Netherlands given how many windmills I seem to go tilting at…

wonkazoo is offline  
Old 2nd May 2019, 05:16
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I cannot speak as an expert in Boeing's technical capabilities, however I did find this article useful in understanding some of the rationale behind the decision to implement MCAS.

MCAS Rationale

The origin must be as a result of trying to squeeze more fuel efficiency out of the airframe by moving the engines forward and upward and changing the nacelle design. (As described by Boeing to AA Pilots recently)

Perhaps an AA pilot might be prepared to share the input.

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Old 2nd May 2019, 05:23
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I appreciate your attempt to clarify the origins of MCAS, but fear it may not get very far. Most of the information that has emerged has been from secondary sources, since all of the primary sources are in legal lock-down.

The Seattle Times has some excellent articles, though the firewall prevents unlimited monthly reading. This one has a lot to say about the bungled safety case, though not the reason for MCAS itself: https://www.seattletimes.com/busines...ion-air-crash/

The best technical description is on b737.org.uk: 737 MAX - MCAS
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Old 2nd May 2019, 06:09
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Originally Posted by GordonR_Cape
I appreciate your attempt to clarify the origins of MCAS, but fear it may not get very far.
At some level you are probably right, but I recognize PPRuNe as a unique resource, one singularly knowledgeable and capable on this particular topic.

Anyway if we don't have original sources then we go to plan B: Assemble all available evidence and make inferences to find the basic truth.

There is far more to this quest than just this question. I suppose I could throw it all out there, but I fear it would be a 5000 word post, so baby steps...

Let's work together and nail down this story. Everyone interested will benefit in the long-run.


Warm regards,
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