5 ms·

Facts: 1. Boeing was running multiple studies to replace the 737 -- and possibly the 757 with the same plane -- https://web.archive.org/web/20090615055919/http

by chx 4y ago

Facts: 1. Boeing was running multiple studies to replace the 737 -- and possibly the 757 with the same plane -- https://web.archive.org/web/20090615055919/http://www.flightglobal.com/articles/2006/02/07/204506/the-737-story-smoke-and-mirrors-obscure-737-and-airbus-a320-replacement.html https://web.archive.org/web/20090615055919/http://www.flight... 2. Boeing Chairman President and Chief Executive Officer Jim McNerney in 2011 February said > We’re gonna do a new airplane. We’re not done evaluating this whole situation yet, but our current bias is to not re-engine, is to move to an all-new airplane at the end of the decade, or the beginning of the next decade. For source, put that quote into Google, it's everywhere. 3. Less than a year later, Southwest Airlines bought 150 of this very re-engineered plane. The 737 replacement plane disappeared. The 757 still has no replacement, twenty years after it was canned. The hole this created for the above 200 seats segment is well visible: https://i.stack.imgur.com/Qc47G.jpg https://i.stack.imgur.com/Qc47G.jpg (I posted this image to SE after digging it out of some ancient blog post) 4. The MCAS system exists because SWA insisted on no retraining > Not only did Southwest management not want their pilots who flew the earlier model 737 NG to have to train in a flight simulator for the MAX, they insisted to Boeing that even classroom training be off the table, the filing shows. Southwest insisted on a clause in the sales contract stipulating a penalty of $1 million per airplane delivered if that standard wasn’t met. https://www.seattletimes.com/business/boeing-aerospace/legal-filing-reveals-southwest-airlines-proposed-a-ploy-to-deceive-faa-on-boeing-737-max/ https://www.seattletimes.com/business/boeing-aerospace/legal... Rumor: It was Southwest Airlines threatening Boeing to buy Airbus instead if it delivered anything but a 737 to them that created the 737 MAX in the first place. Now you know how far a single-plane airline would go to avoid buying a different plane.

msbarnett 4y ago
> The MCAS system exists because SWA insisted on no retraining This is somewhat inaccurate (and appears to trade on the oft-repeated but completely incorrect misunderstanding that the MCAS acts as a sort of “normal 737 emulator”). In fact, the MCAS exists because without it the MAX would be 100% uncertifiable for commercial flight. The central problem is that, due to the lopsided aerodynamics of the MAX, as the nose of the MAX moves up and approaches a stall, the forces on the pilot’s stick “invert” such that it becomes easier to continue to pull into the stall than push away from the stall. Commercial aircraft are not allowed to have inverted stick forces at any angle. When Boeing realized this, they decided to implement a kind of hack that would use the trim to put pressure on the nose downwards to counteract the forces on the stick such that they never invert. The MCAS is the system that commands this downwards trim. The desire to avoid retraining led Boeing to conceal the existence of the MCAS, but it is not why it exists. The plane flatly is uncertifiable without it. No amount of training would change this, as inverted stick forces are a failure of fundamental airworthiness requirements.
- gomijacogeo 4y ago
  The plane should have also been uncertifiable as MCAS lacked sufficient redundancy in air data or computing for so much control authority. It's not clear whether this was deliberately concealed by Boeing or if they had just lost the institutional memory to know that this solution was inherently unsafe.
- GekkePrutser 4y ago
  > The plane flatly is uncertifiable without it. No amount of training would change this, as inverted stick forces are a failure of fundamental airworthiness requirements. I didn't know that. In that case though, would it even be allowed to disable MCAS as part of any SOP? As far as I recall the documentation did mention one obscure process indicating to the pilot to disable MCAS when it acted up like it did during the accidents. But I can't imagine it would be allowed to even have this as an operating procedure this when it puts the plane in a situation where it can't be certified? The whole thing is such a mess... It's clear they should have just redesigned the whole airframe to modern standards IMO.
  - salawat 4y ago
    >But I can't imagine it would be allowed to even have this as an operating procedure this when it puts the plane in a situation where it can't be certified? Anything can be allowed with enough omission, lawyers, scapegoating, campaign donations, and enough tolerance for blood on one's hands. It's called regulatory capture and it's the fundamental conflict-of-interest between most engineering orgs and their in house Quality programs, with the exacerbating effect that if you can coerce the external regulatory forces to give you a pass, there's really nothing your Quality people can do but resign in a gesture of "I won't build that". You will never see the regulatory apparatus work as designed if it isn't willing to just say "No" to that which clearly violates prescriptive certification criteria.
  - tzs 4y ago
    As was mentioned earlier, MCAS exists to modify the stick forces in certain circumstances. Those circumstances never occur in anything near normal flight. And if they do occur it is not like the stick force deviation from what regulations allows makes the plane not flyable. I've seen it described by pilots who have tested it as it makes it have a slightly softer feel for stall recovery. When the European Union Aviation Safety Agency was testing it for return to service they did full flights tests with and without MCAS and found that it was fine both ways [1]. So if something goes wrong with MCAS during a flight making it interfere with normal operation of the aircraft, then disabling it is quite reasonable. The odds that you will end up later in a situation where MCAS actually has to do something are extremely low, and the odds are even lower that the pilots won't be be able to handle it without the help from MCAS. And that's assuming you are in a stage of flight where it would even be used. MCAS is only active when flaps are up and the autopilot is disengaged, so most of the time for most flights it is out of the picture. MCAS seems to be one of those things that needs to have great care taken in its implementation because the danger from it mistakenly activating when it should not seems to be orders of magnitude higher than amount of safety benefit it provides when it correctly activates. They did not take that great care. [1] https://theaircurrent.com/aircraft-development/mcas-may-not-have-been-needed-on-the-737-max-at-all/ https://theaircurrent.com/aircraft-development/mcas-may-not-...

by chx 4y ago

msbarnett 4y ago

> The MCAS system exists because SWA insisted on no retraining This is somewhat inaccurate (and appears to trade on the oft-repeated but completely incorrect misunderstanding that the MCAS acts as a sort of “normal 737 emulator”). In fact, the MCAS exists because without it the MAX would be 100% uncertifiable for commercial flight. The central problem is that, due to the lopsided aerodynamics of the MAX, as the nose of the MAX moves up and approaches a stall, the forces on the pilot’s stick “invert” such that it becomes easier to continue to pull into the stall than push away from the stall. Commercial aircraft are not allowed to have inverted stick forces at any angle. When Boeing realized this, they decided to implement a kind of hack that would use the trim to put pressure on the nose downwards to counteract the forces on the stick such that they never invert. The MCAS is the system that commands this downwards trim. The desire to avoid retraining led Boeing to conceal the existence of the MCAS, but it is not why it exists. The plane flatly is uncertifiable without it. No amount of training would change this, as inverted stick forces are a failure of fundamental airworthiness requirements.

gomijacogeo 4y ago
The plane should have also been uncertifiable as MCAS lacked sufficient redundancy in air data or computing for so much control authority. It's not clear whether this was deliberately concealed by Boeing or if they had just lost the institutional memory to know that this solution was inherently unsafe.
GekkePrutser 4y ago
> The plane flatly is uncertifiable without it. No amount of training would change this, as inverted stick forces are a failure of fundamental airworthiness requirements. I didn't know that. In that case though, would it even be allowed to disable MCAS as part of any SOP? As far as I recall the documentation did mention one obscure process indicating to the pilot to disable MCAS when it acted up like it did during the accidents. But I can't imagine it would be allowed to even have this as an operating procedure this when it puts the plane in a situation where it can't be certified? The whole thing is such a mess... It's clear they should have just redesigned the whole airframe to modern standards IMO.
- salawat 4y ago
  >But I can't imagine it would be allowed to even have this as an operating procedure this when it puts the plane in a situation where it can't be certified? Anything can be allowed with enough omission, lawyers, scapegoating, campaign donations, and enough tolerance for blood on one's hands. It's called regulatory capture and it's the fundamental conflict-of-interest between most engineering orgs and their in house Quality programs, with the exacerbating effect that if you can coerce the external regulatory forces to give you a pass, there's really nothing your Quality people can do but resign in a gesture of "I won't build that". You will never see the regulatory apparatus work as designed if it isn't willing to just say "No" to that which clearly violates prescriptive certification criteria.
- tzs 4y ago
  As was mentioned earlier, MCAS exists to modify the stick forces in certain circumstances. Those circumstances never occur in anything near normal flight. And if they do occur it is not like the stick force deviation from what regulations allows makes the plane not flyable. I've seen it described by pilots who have tested it as it makes it have a slightly softer feel for stall recovery. When the European Union Aviation Safety Agency was testing it for return to service they did full flights tests with and without MCAS and found that it was fine both ways [1]. So if something goes wrong with MCAS during a flight making it interfere with normal operation of the aircraft, then disabling it is quite reasonable. The odds that you will end up later in a situation where MCAS actually has to do something are extremely low, and the odds are even lower that the pilots won't be be able to handle it without the help from MCAS. And that's assuming you are in a stage of flight where it would even be used. MCAS is only active when flaps are up and the autopilot is disengaged, so most of the time for most flights it is out of the picture. MCAS seems to be one of those things that needs to have great care taken in its implementation because the danger from it mistakenly activating when it should not seems to be orders of magnitude higher than amount of safety benefit it provides when it correctly activates. They did not take that great care. [1] https://theaircurrent.com/aircraft-development/mcas-may-not-have-been-needed-on-the-737-max-at-all/ https://theaircurrent.com/aircraft-development/mcas-may-not-...