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Ironically, I believe that your information is also inaccurate. MCAS is required in order to meet federal airworthiness requirements. Without it, in certain fli

Ironically, I believe that your information is also inaccurate. MCAS is required in order to meet federal airworthiness requirements. Without it, in certain flight conditions the back-pressure on the control yoke gets less as the yoke is pulled further back. It's like over-steer in a car, and is simply not allowed. Yes, the plane is dynamically stable; if you leave the yoke in one position it won't pitch up even more. However, the forces must be corrected somehow, regardless of type rating concerns. "The 737 MAX was a bit too easy to pull into a stall when flying with high AoA and making abrupt maneuvers. The larger engines for the MAX hung further forward from the wing, added a destabilizing aerodynamic area ahead of the center of gravity, destabilizing the pitch moment curve at high AoA. Boeing and the certification authority, FAA, decided added margins was called for. Boeing added a pitch augmentation at high AoA called Maneuvering Characteristics Augmentation System, MCAS. The aircraft should trim nose down to increase the stick force needed once it passed into the light grey area where the base aircraft had a region of less stability. Before the augmentation, the pilot felt if the aircraft wanted to fly into the stall, it got easier to increase the AoA after 12°AoA. With the augmentation the felt extra force was the same for the first and last part of the curve before the maximum lift was achieved at stall (and stall warning kicked in)." [0] The manner of the fix (MCAS transparently pushing the nose down) was designed to avoid pilot retraining and thus keep the same type rating. Edit: The fact that the 737-Max needs a handling tweak is not a failure. Modern planes have all kinds of these tweaks, whether aerodynamic (such as strakes), mechanical (stick shakers) or enabled in software. As the cited article continues: "So far so good. It's common an aircraft’s flight control system has fixes to stability margin changes in different parts of the flight envelope." The problem is that Boeing had a pretty severe collapse of its systems engineering regime. "The implementation for the 737 MAX had two problems, however: - The fault checking of the triggering AoA signal was not rigorous enough. This problem has been discussed a lot. No need to add anything. - The judgment the pilots would identify a problem with the augmentation as a trim runaway and shut the trim off was wrong. Why the pilots didn’t see MCAS rouge actions as a trim runaway is poorly understood." (The article was published in February. Since then lots of information has come to light about how MCAS determinedly fought correction, and the huge mental and physical loads imposed on the pilots.) Edit 2: FAA regulation mandating increasing elevator forces for all transport aircraft: FAR §25.253 High-speed characteristics, (a) Speed increase and recovery characteristics, (3): With the airplane trimmed at any speed up to VMO/MMO [maximum operating airspeed], there must be no reversal of the response to control input about any axis at any speed up to VDF/MDF [maximum airspeed demonstrated in testing]. Any tendency to pitch, roll, or yaw must be mild and readily controllable, using normal piloting techniques. When the airplane is trimmed at VMO/MMO, the slope of the elevator control force versus speed curve need not be stable at speeds greater than VFC/MFC [maximum control airspeed], but there must be a push force at all speeds up to VDF/MDF and there must be no sudden or excessive reduction of elevator control force as VDF/MDF is reached. [1] [0] https://leehamnews.com/2019/02/08/bjorns-corner-pitch-stability-part-9/ https://leehamnews.com/2019/02/08/bjorns-corner-pitch-stabil... [1] https://www.ecfr.gov/cgi-bin/text-idx?node=14:1.0.1.3.11#se14.1.25_1203 https://www.ecfr.gov/cgi-bin/text-idx?node=14:1.0.1.3.11#se1...

nobodyandproud 7y ago
I don’t think this is correct. Your reference suggests that this tweak is to match the expectations of pilots certified to fly 737s, which handle in a certain way.
- mgsouth 7y ago
  See edit 2, citing regulation which must be met by all transport aircraft. I think also §25.255 Out-of-trim characteristics, (b) (1) The stick force vs. g curve must have a positive slope at any speed up to and including VFC/MFC
  - nobodyandproud 7y ago
    I don’t see how the FAAs assessment that the 737 MAX was easier to put into a stall for greater that 12 degrees AoA is the same as a “reversal of controls” or a “sudden or excessive reduction of elevator control” stipulated in 25.253 What am I missing? I am not an aviation expert in any sense.
    - mgsouth 7y ago
      "Reversal of control force", not "reversal of controls". There's also section 25.175, which stipulates "The stick force curve must have a stable slope at speeds"... and gives speed ranges for climb, cruise, approach, and landing. For example: §25.175 Demonstration of static longitudinal stability. Static longitudinal stability must be shown as follows: (a) Climb. The stick force curve must have a stable slope at speeds between 85 and 115 percent of the speed at which the airplane— (1) Is trimmed, with— (i) Wing flaps retracted; (ii) Landing gear retracted; (iii) Maximum takeoff weight; and (iv) 75 percent of maximum continuous power for reciprocating engines or the maximum power or thrust selected by the applicant as an operating limitation for use during climb for turbine engines; and (2) Is trimmed at the speed for best rate-of-climb except that the speed need not be less than 1.3 VSR These are transports, not fighters. The basic idea is that you want it to be harder work to make a sharper maneuver, and want the aircraft to naturally level out. If the force required decreases for a steeper pitch/roll/yaw, then the plane will naturally want to intensify the maneuver. It's like a car with oversteer--let go of the steering wheel and it will make a sharper turn. As the article cited said, the FAA and Boeing's test pilots weren't happy with the yoke forces in certain situations.

nobodyandproud 7y ago

I don’t think this is correct. Your reference suggests that this tweak is to match the expectations of pilots certified to fly 737s, which handle in a certain way.

mgsouth 7y ago
See edit 2, citing regulation which must be met by all transport aircraft. I think also §25.255 Out-of-trim characteristics, (b) (1) The stick force vs. g curve must have a positive slope at any speed up to and including VFC/MFC
- nobodyandproud 7y ago
  I don’t see how the FAAs assessment that the 737 MAX was easier to put into a stall for greater that 12 degrees AoA is the same as a “reversal of controls” or a “sudden or excessive reduction of elevator control” stipulated in 25.253 What am I missing? I am not an aviation expert in any sense.
  - mgsouth 7y ago
    "Reversal of control force", not "reversal of controls". There's also section 25.175, which stipulates "The stick force curve must have a stable slope at speeds"... and gives speed ranges for climb, cruise, approach, and landing. For example: §25.175 Demonstration of static longitudinal stability. Static longitudinal stability must be shown as follows: (a) Climb. The stick force curve must have a stable slope at speeds between 85 and 115 percent of the speed at which the airplane— (1) Is trimmed, with— (i) Wing flaps retracted; (ii) Landing gear retracted; (iii) Maximum takeoff weight; and (iv) 75 percent of maximum continuous power for reciprocating engines or the maximum power or thrust selected by the applicant as an operating limitation for use during climb for turbine engines; and (2) Is trimmed at the speed for best rate-of-climb except that the speed need not be less than 1.3 VSR These are transports, not fighters. The basic idea is that you want it to be harder work to make a sharper maneuver, and want the aircraft to naturally level out. If the force required decreases for a steeper pitch/roll/yaw, then the plane will naturally want to intensify the maneuver. It's like a car with oversteer--let go of the steering wheel and it will make a sharper turn. As the article cited said, the FAA and Boeing's test pilots weren't happy with the yoke forces in certain situations.