Transponder Based Landing System.
DEPARTMENT OF THE ARMY WASHINGTON D C
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An air traffic control system wherein a ground based interrogatorreceiver interrogates an aircraft transponder which, in addition to responding to the interrogation, also transmits automatic encoded altitude information. The interrogatorreceiver unit processes the received signal to derive relative azimuth and range information of the interrogated aircraft and to decode the altitude information to provide the aircraft reported altitude signal. The aircraft reported altitude signal is compared to the selected glide path height which is a function of the range that the approaching aircraft is from the runway touchdown point. The difference is noted on a glide scope meter. By observing the azimuth and range reading, and also the deflection from zero on the glide scope meter, the controller will be able to inform the aircraft pilot of the approaching aircraft position relative to runway center line, glide path and distance from touchdown. Author