Development of the civil aeronautics authority instrument landing system at Indianapolis

The history of the development of blind-landing devices since 1928 sketched, and a full description follows of radio system installed at Indianapolis by International Telephone Development Co. In this system 4 complete sets of apparatus are installed to facilitate landing from 4 directions 4 elements are required for each direction a localizer for lateral guidance, a radio glide path for descent and 2 markers to indicate progress along the course. Ultra-short waves are used throughout. The arrangements for the various signals are briefly described, including the glide path, which is made straight until the runway is approached, when its slope is gradually reduced; the layout on the airfield is given in detail. Experiment with different widths of the constant-intensity path guiding the pilot shows that much narrower paths are desirable than those formerly used. Horizontal polarization, completely free from any vertical component, is best used, a small percentage of vertical resulting in an ambiguous course. The receiving equipment in the aircraft, the information gained from tests and the views of pilots on desirable improvements, are described and discussed.