ESDU 83024 examines the relationship between the coefficients of the stability quartic of the lateral equations of motion and the coefficients of the equivalent quadratic factors. Relationships are developed that@ in some cases@ allow approximate solutions of the modes of response of an unaugmented aircraft to be obtained directly from the coefficients of the quartic equation. These same relationships are shown to apply to an aircraft equipped with an idealised (that is@ one without lags) yaw damper. A method is described for investigating the effects of the dynamic response of a second-order yaw damper on the stability of an aircraft/autostabiliser combination. The method is based on the study of constant-damping curves obtained in a plane defined by two of the yaw damper parameters. The Dutch roll approximation is again used to simplify the analysis such that optimum autostabiliser natural frequency and damping ratio values can be obtained for a given gearing or a given damping requirement.