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> These engines moving made the plane more vulnerable to a stall situation. I don't think this is correct. A lot is being made about the engine move with rega

> These engines moving made the plane more vulnerable to a stall situation. I don't think this is correct. A lot is being made about the engine move with regard to aerodynamic behavior, but it doesn't seem at all outside of the bounds of what is considered standard. Pilots report that a similar 'light stick feel' at high AoA is already present in aircraft like the 757. It's not that the aerodynamic change was worse or better, it's simply that it was a change at all. MCAS was there to satisfy the type rating. MCAS is not anti-stall. The crucial mistake appears to be the extreme failure mode of the system; it is permitted to input high stabilizer trim angles without limit. Without any kind of restriction, the failure goes from annoying (pull up on flight stick + fiddle with stab control until you solve it) to the deadly crashes we've seen where pilots are in extremely tricky situations. The fix could be as simple as making MCAS cutout in the case of an AoA disagree (no real hardware changes here) as well as limiting the input of extreme trim angles.

cletus 7y ago
> It's not that the aerodynamic change was worse or better, it's simply that it was a change at all. It seems you are correct [1]: > MCAS is a longitudinal stability enhancement. It is not for stall prevention (although indirectly it helps) or to make the MAX handle like the NG (although it does); it was introduced to counteract the non-linear lift generated by the LEAP-1B engine nacelles at high AoA and give a steady increase in stick force as the stall is approached as required by regulation. [1] http://www.b737.org.uk/mcas.htm http://www.b737.org.uk/mcas.htm
Scaevolus 7y ago
> MCAS was there to satisfy the type rating. MCAS is not anti-stall. MCAS's only observable intervention is to push the nose down to prevent stall, which means it is by definition anti-stall. Boeing says MCAS is an acronym for "Maneuvering Characteristics Augmentation System", but a better name for MCAS is "Machine Controlled Anti Stall". https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Augmentation_System https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Au...
- mannykannot 7y ago
  While the effect of pushing the nose down is an all-too observable effect, that its purpose is stall prevention is not directly observable. According to this article[1], the intended purpose was to restore the back-force needed to put the airplane in a stall, as the effect of the new engines was to make the control feel lighter at high AofA. The article also discusses the certification requirements with regard to acceptable handling characteristics. FWIW, Boeing CEO Dennis Muilenburg is quoted in [2] as saying that "When you take a look at the original design of the MCAS system. I think in some cases, in the media, it has been reported or described as an anti-stall system, which it is not. It's a system that's designed to provide handling qualities for the pilot that meet pilot preferences. "We want the airplane to behave in the air similar to the previous generation of 737s. That's the preferred pilot feel for the airplane, and MCAS is designed to provide those kinds of handling qualities at a high angle of attack." Of course, the elephant in the room not being mentioned here is whether Boeing's primary motive for replicating the handling characteristics of earlier versions of 737s was an overriding concern with avoiding pilot training. [1] https://leehamnews.com/2019/02/15/bjorns-corner-pitch-stability-part-10-wrap-up/ https://leehamnews.com/2019/02/15/bjorns-corner-pitch-stabil... [2] https://www.businessinsider.com/boeings-ceo-on-why-737-max-pilots-not-told-of-mcas-2019-4 https://www.businessinsider.com/boeings-ceo-on-why-737-max-p...
  - roelschroeven 7y ago
    One of the requirements for an airplane to receive a certification is that the pilot needs to put more and more pressure on the stick to achieve higher and higher angle of attack. If at some point the airplane starts to pitch to higher AoA without extra pressure from the pilot, that's a big no. Reason: otherwise it would be all too easy to inadvertently enter a stall condition. Boeing 737 MAX without MCAS violates that requirement (caused by the lift generated by large engine nacelles in front of the wings). MCAS is indeed designed to restore that required back-force. Back-force that is required to prevent stalls. I suppose one could debate whether the stall prevention effect of MCAS is direct or indirect. But I don't think it's debatable that it is designed to comply with a certification requirement that's intended to help prevent stalls.
mannykannot 7y ago
> It's not that the aerodynamic change was worse or better... Having the control get 'lighter' (more sensitive to increased back-force) as one approaches the stall is definitely an undesirable characteristic, as it increases the risk of a distracted pilot stalling. While a change in the opposite direction might have been problematic (insofar as additional training is a problem), the way it actually goes is more likely to prompt the FAA to require something be done about it.

cletus 7y ago

> It's not that the aerodynamic change was worse or better, it's simply that it was a change at all. It seems you are correct [1]: > MCAS is a longitudinal stability enhancement. It is not for stall prevention (although indirectly it helps) or to make the MAX handle like the NG (although it does); it was introduced to counteract the non-linear lift generated by the LEAP-1B engine nacelles at high AoA and give a steady increase in stick force as the stall is approached as required by regulation. [1] http://www.b737.org.uk/mcas.htm http://www.b737.org.uk/mcas.htm

Scaevolus 7y ago

> MCAS was there to satisfy the type rating. MCAS is not anti-stall. MCAS's only observable intervention is to push the nose down to prevent stall, which means it is by definition anti-stall. Boeing says MCAS is an acronym for "Maneuvering Characteristics Augmentation System", but a better name for MCAS is "Machine Controlled Anti Stall". https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Augmentation_System https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Au...

mannykannot 7y ago
While the effect of pushing the nose down is an all-too observable effect, that its purpose is stall prevention is not directly observable. According to this article[1], the intended purpose was to restore the back-force needed to put the airplane in a stall, as the effect of the new engines was to make the control feel lighter at high AofA. The article also discusses the certification requirements with regard to acceptable handling characteristics. FWIW, Boeing CEO Dennis Muilenburg is quoted in [2] as saying that "When you take a look at the original design of the MCAS system. I think in some cases, in the media, it has been reported or described as an anti-stall system, which it is not. It's a system that's designed to provide handling qualities for the pilot that meet pilot preferences. "We want the airplane to behave in the air similar to the previous generation of 737s. That's the preferred pilot feel for the airplane, and MCAS is designed to provide those kinds of handling qualities at a high angle of attack." Of course, the elephant in the room not being mentioned here is whether Boeing's primary motive for replicating the handling characteristics of earlier versions of 737s was an overriding concern with avoiding pilot training. [1] https://leehamnews.com/2019/02/15/bjorns-corner-pitch-stability-part-10-wrap-up/ https://leehamnews.com/2019/02/15/bjorns-corner-pitch-stabil... [2] https://www.businessinsider.com/boeings-ceo-on-why-737-max-pilots-not-told-of-mcas-2019-4 https://www.businessinsider.com/boeings-ceo-on-why-737-max-p...
- roelschroeven 7y ago
  One of the requirements for an airplane to receive a certification is that the pilot needs to put more and more pressure on the stick to achieve higher and higher angle of attack. If at some point the airplane starts to pitch to higher AoA without extra pressure from the pilot, that's a big no. Reason: otherwise it would be all too easy to inadvertently enter a stall condition. Boeing 737 MAX without MCAS violates that requirement (caused by the lift generated by large engine nacelles in front of the wings). MCAS is indeed designed to restore that required back-force. Back-force that is required to prevent stalls. I suppose one could debate whether the stall prevention effect of MCAS is direct or indirect. But I don't think it's debatable that it is designed to comply with a certification requirement that's intended to help prevent stalls.

mannykannot 7y ago

> It's not that the aerodynamic change was worse or better... Having the control get 'lighter' (more sensitive to increased back-force) as one approaches the stall is definitely an undesirable characteristic, as it increases the risk of a distracted pilot stalling. While a change in the opposite direction might have been problematic (insofar as additional training is a problem), the way it actually goes is more likely to prompt the FAA to require something be done about it.