691,017. Radio navigation. SPERRY CORPORATION. Jan. 12, 1951 FFeb 17, 1950; March 10, 1950], No. 935/51. Class 40 (vii). A radio system for assisting aircraft landing comprises means for combining signals received from a landing path receiver (representing displacement in a vertical plane from a glide path) and signals from a pitch indicating instrument (representing angular deviation from a predetermined attitude) and supply the combined signals to an instrument or auto-pilot and a switch for rendering the instrument or autopilot responsive to the pitch signals only, together with a normally ineffective bias providing a fly-up indication or control. In a first embodiment, Fig. 1 (not shown), the output from a glide path receiver is mixed with a pitch signal obtained from a gyro vertical and the combined signals fed to the horizontal movement of a cross-pointer meter. The vertical pointer movement is similarly fed by the combined signals from a radio localizer beam receiver, a compass, and the bank axis of the gyro vertical. A three-position switch is provided in the second position of which signals from the glide-path receiver are disconnected from the first combining circuit and replaced by a manually adjustable signal providing a fly-up bias to the meter and the localizer receiver signals applied to the other combining circuit are reduced in amplitude to limit any bank angle indication and also subjected to the control of course softening means. In the third switch position the control of the horizontal pointer movement is the same as in the second position but signals from the localizer receiver are completely disconnected from the vertical pointer movement. As the switch is provided to make the change-over necessary to obtain suitable fly-up signals when it has been decided not to follow the glide-path to a touch but to overshoot the runway it is suggested that it be mounted on the throttle lever so that the engine power may be increased and the switch operated at the same time. In an embodiment including an automatic pilot (Fig. 4) the compass unit 101 feeds one input of the turn control mixer 105 whose output is applied to the rudder servomotor 104. The craft's attitude control is derived from gyrovertical 102 having separate pitch and roll pick-offs. The roll pick-off directly controls the aileron servomotor 110 and also provides an input through bank integrator 111 to the mixer 105. The pitch pick-off from the gyro controls the elevator servomotor in conjunction with other apparatus. Two switch controls are provided, manual selector switch 121 operating ganged 3-position switches 122, 123, 124, and 125; and switch 127 which operates by means of energizing coil 129, switch banks 130, 131, 132, 133 and 134. In its first (uppermost) position the manual selector switch applies signals from range or localizer receiver 118 to the turn control mixer 105, energizes the circuit of switch 127 and coil 129, and de-energizes coil 115<SP>1</SP> so that manual pitch control 114 is ineffective. In addition signals from glide path receiver 120 are being applied together with the pitch control signals to the elevator servomotor. This is the position of the selector switch for landing the craft. If, however, it is desired not to touch down after commencing to follow the landing path operation of switch 127 will in turn operate switches 130-134 and hold them operated by means of the circuit through 133. Switch 130 disconnects the signals from receiver 118 from the turn control mixer and substitutes manual control 107, 131 makes manual pitch control 114 operative so that the craft may be once more flown upwards and switches 132 and 134 energize motor 141 which drives potentiometer arm 143 through slip clutch 156, causing the effect of the glide path receiver signals to be made progressively less and finally shorted out completely. Warning light 170 is also lit while the switches 130-134 are closed. When the last-mentioned switches are released, as by movement of selector switch 121 to another position, current through motor 141 is reversed and it runs backwards moving potentiometer arm 143 to the " right-hand " position until the cam-operated contacts of homing switch 161 break the circuit. The second position of the selector switch provides for feeding signals from receiver 118 to turn control mixer 105, rendering manual pitch control 114 effective and shorting the output of glide-path receiver 120. In the third position manual controls 107 and 114 are effective in neither receiver. In either the second or third positions altimeter 113 may be switched in by means of switch 126 to maintain a given elevation. Specifications 599,254, 660,559, [Group XXXV], and 690,985 are referred to.