Originally Posted by
yoko1
The phrase "anti-stall" falls into the much the same category as "unstable." It is not a defined term for the purposes of the aircraft certification. While we can use it generically for any system or device that helps in the prevention of or recovery from stalls, it does not correspond to any particular certification requirement. There are requirements for stall warning devices and handling characteristics approaching and during a stall that are spelled out in detail in FAR Part 25, and it is those requirements that Boeing will point to when they explain why MCAS was needed.
In particular, FAR Part 25 make frequent references for the requirement that "the stick force curve must have a stable slope" in various flight regimes and that approaching a stall the "longitudinal control force must be positive up to and throughout the stall." The requirement for a "stable slope" in particular is what drove the need for MCAS.
From
BA - I assume you are either directly or indirectly on their payroll:
As airspeed varies from a trimmed condition, the column force required to maintain a new speed (without re-trimming) is a measure of static longitudinal stability. For any conventional airplane, the location of the CG has the strongest influence on static longitudinal stability. For a statically stable airplane the required column force, as speed varies from the trimmed condition, is less at an aft CG than it is at a forward CG. The minimum average gradient allowed by U.S. Federal Aviation Administration FAR Part 25 is one pound for each six knots. As the CG moves aft (BDAttitude: or center of lift moves forward), it reaches a point where the stick force per knot drops to zero, then reverses. This location is called the neutral point.The difference between the actual CG location and the neutral point is called the static margin. With a CG forward of the neutral point, an airplane has a positive static margin and positive static longitudinal stability. At a CG aft of the neutral point, an airplane has a negative static margin, is statically unstable, and requires some form of augmentation to be flown with an acceptable workload.
So I will not call it "unstable" but "smaller than required or negative static margin hence not stable enough to be certifyable".
Never the less it is a stability problem not a handling beauty contest as you would like to spin it.