5 ms·

No need. The plane is perfectly flyable without MCAS. It just handles differently to other 737s in parts of the flight envelope.

by foldr 7y ago

sokoloff 7y ago
There is a legal need (to pass 25.173 requirements). The Max doesn't have MCAS because it feels different from another 737; it has MCAS because it feels different from the legal requirement to certify any civilian transport aircraft.
- jsjohnst 7y ago
  > has MCAS because it feels different from the legal requirement to certify any civilian transport aircraft Source for that claim? I’ve read extensively on the topic and have internal Boeing sources and everything I’ve seen says MCAS was needed to maintain the type rating, not that without MCAS the plane wasn’t airworthy.
  - sokoloff 7y ago
    25.173.a requires the aircraft to meet this section at speeds as low as the minimum speed for steady unstalled flight. 25.173.c requires the stick force curve to have a stable and minimum slope of 1 lbf/6 knots. At high angles of attack (low speeds), the stick force reduces slightly as compared to lower angles of attack (higher speeds). This requires a negative slope at a point on the stick force curve, violating both the minimum slope and the stable slope requirement of 25.173. (indirect source: https://www.wsj.com/articles/how-boeings-737-max-failed-11553699239?mod=hp_lead_pos9 https://www.wsj.com/articles/how-boeings-737-max-failed-1155... ). They couch it as "pushes the nose up" (though the image cited is dual sourced to Boeing and a WSJ graphics author, so I'll wager that "pushes the nose up" is WSJ content rather than Boeing content).
- foldr 7y ago
  I've never seen the claim regarding 25.173 properly sourced.
  - sokoloff 7y ago
    Don't know if any of these will satisfy or not, in advance of a final NTSB/FAA/Boeing finalization/post-mortem (I doubt all the internal docs are ever going to come out, of course): http://newsinflight.com/2019/03/29/what-causes-boeing-737max-to-stall/ http://newsinflight.com/2019/03/29/what-causes-boeing-737max... https://abnormaldistribution.org/index.php/2019/04/30/ieee-spectrum-on-possible-software-involvement-in-two-recent-airliner-crashes/ https://abnormaldistribution.org/index.php/2019/04/30/ieee-s... https://www.quora.com/Does-the-fact-that-the-pilots-of-the-737-Max-that-crashed-in-Algeria-tried-several-times-to-stop-the-plane-nosediving-mean-there-is-something-seriously-wrong-with-MCAS/answer/Alan-Dicey https://www.quora.com/Does-the-fact-that-the-pilots-of-the-7... https://seekingalpha.com/article/4286602-boeing-737-max-misconceptions-engineers-view https://seekingalpha.com/article/4286602-boeing-737-max-misc...

No need. The plane is perfectly flyable without MCAS. It just handles differently to other 737s in parts of the flight envelope.

by foldr 7y ago

No need. The plane is perfectly flyable without MCAS. It just handles differently to other 737s in parts of the flight envelope.

sokoloff 7y ago

There is a legal need (to pass 25.173 requirements). The Max doesn't have MCAS because it feels different from another 737; it has MCAS because it feels different from the legal requirement to certify any civilian transport aircraft.

jsjohnst 7y ago
> has MCAS because it feels different from the legal requirement to certify any civilian transport aircraft Source for that claim? I’ve read extensively on the topic and have internal Boeing sources and everything I’ve seen says MCAS was needed to maintain the type rating, not that without MCAS the plane wasn’t airworthy.
- sokoloff 7y ago
  25.173.a requires the aircraft to meet this section at speeds as low as the minimum speed for steady unstalled flight. 25.173.c requires the stick force curve to have a stable and minimum slope of 1 lbf/6 knots. At high angles of attack (low speeds), the stick force reduces slightly as compared to lower angles of attack (higher speeds). This requires a negative slope at a point on the stick force curve, violating both the minimum slope and the stable slope requirement of 25.173. (indirect source: https://www.wsj.com/articles/how-boeings-737-max-failed-11553699239?mod=hp_lead_pos9 https://www.wsj.com/articles/how-boeings-737-max-failed-1155... ). They couch it as "pushes the nose up" (though the image cited is dual sourced to Boeing and a WSJ graphics author, so I'll wager that "pushes the nose up" is WSJ content rather than Boeing content).
foldr 7y ago
I've never seen the claim regarding 25.173 properly sourced.
- sokoloff 7y ago
  Don't know if any of these will satisfy or not, in advance of a final NTSB/FAA/Boeing finalization/post-mortem (I doubt all the internal docs are ever going to come out, of course): http://newsinflight.com/2019/03/29/what-causes-boeing-737max-to-stall/ http://newsinflight.com/2019/03/29/what-causes-boeing-737max... https://abnormaldistribution.org/index.php/2019/04/30/ieee-spectrum-on-possible-software-involvement-in-two-recent-airliner-crashes/ https://abnormaldistribution.org/index.php/2019/04/30/ieee-s... https://www.quora.com/Does-the-fact-that-the-pilots-of-the-737-Max-that-crashed-in-Algeria-tried-several-times-to-stop-the-plane-nosediving-mean-there-is-something-seriously-wrong-with-MCAS/answer/Alan-Dicey https://www.quora.com/Does-the-fact-that-the-pilots-of-the-7... https://seekingalpha.com/article/4286602-boeing-737-max-misconceptions-engineers-view https://seekingalpha.com/article/4286602-boeing-737-max-misc...