You're confusing aerodynamicist's idea of stability with the regulatory idea of stability. I.e. You're in the wrong namespace.
To be said to be stable, and certifiable as a Civil Transport Aircraft, an airframe must pass all relevant prescriptive tests as specified in the FAR's.
FAR 25.173(c) is not demonstrated without MCAS, and therefore in regulatory parlance, not necessarily aerodynamic parlance, the aircraft is unstable by virtue of failing to demonstrate longitudinal stability as specifically prescribed in the FARs.
The fact that MCAS was added to minimize the risk of losing grandfathered type cert, and the terrible engineering that went into it is just icing on the cake.
The specific behavioral failure occurs during a wind-up turn. If you look up the procedure for the test, one of the independent variables is trim setting. That you have to adjust the trim (an input variable) during the maneuver in order to pass the test (preservation of control stick force response curve characteristics) kind of invalidates the entire endeavor. Never mind that the mechanism you leveraged to pass that corner case can doom the plane in case of false positive activation.
So yes. It may be aerodynamically stable in 98% of the operating envelope, but in order to eke out that last 2 percent, caution was thrown to the winds, and implemented a kludge that was never safely integrated.
Note I'm not arguing against the point you're trying to make. Just pointing out where the confusion in terms is likely arising in translation from technical to layman.
The layman only cares that the regulatory definition is hit, as the regulation is the compromise point between aviation and everyone else's interest in not having craters.
To be said to be stable, and certifiable as a Civil Transport Aircraft, an airframe must pass all relevant prescriptive tests as specified in the FAR's.
FAR 25.173(c) is not demonstrated without MCAS, and therefore in regulatory parlance, not necessarily aerodynamic parlance, the aircraft is unstable by virtue of failing to demonstrate longitudinal stability as specifically prescribed in the FARs.
The fact that MCAS was added to minimize the risk of losing grandfathered type cert, and the terrible engineering that went into it is just icing on the cake.
The specific behavioral failure occurs during a wind-up turn. If you look up the procedure for the test, one of the independent variables is trim setting. That you have to adjust the trim (an input variable) during the maneuver in order to pass the test (preservation of control stick force response curve characteristics) kind of invalidates the entire endeavor. Never mind that the mechanism you leveraged to pass that corner case can doom the plane in case of false positive activation.
So yes. It may be aerodynamically stable in 98% of the operating envelope, but in order to eke out that last 2 percent, caution was thrown to the winds, and implemented a kludge that was never safely integrated.
Note I'm not arguing against the point you're trying to make. Just pointing out where the confusion in terms is likely arising in translation from technical to layman.
The layman only cares that the regulatory definition is hit, as the regulation is the compromise point between aviation and everyone else's interest in not having craters.