velocity component x along the path x of fig1 a and the velocity component y parallel to the y axis are respectively given by equations 1 and 2 equ1 where x is the velocity along the path x u03c6 az is the angular position of the aircraft relative to the plane of the azimuth beam these velocity components may also be given in terms of the projected distance x of the aircraft to the dme transmitter should the distance measuring equipment malfunction an estimate of this distance may be provided that may be utilized to provide estimated component velocities it should be apparent that estimated velocities x e and y e may be given in terms of the estimated distance x e and parameters defined in equation 1 by the equations 3 and 4 respectively equ2 where u03b3 el is the elevation angle of the referenced to the dme transmitter location in the plane of the glide slope beam when the estimated distance x e is equal to the true distance the true and estimated velocity components are equal consequently the ratios of x x e and y y e are measures of the accuracy of the estimated distance thus by a series of successive approximations an estimated distance substantially equal to the true distance may be achieved each successive approximation for x e may be established by selecting the maximum of the x velocity ratio and the y velocity ratio multiplied by the estimated distance utilized for determining those ratios thus in accordance.