Automatic Height Transmission is One Step Closer

Use of automatic height transmission, the essential "third dimension" for use in the control of aircraft, has been brought closer by action taken recently at the Seventh Session of the International Civil Aviation Organization. The Session recommended adoption of technical standards that will: 1) update and improve the existing international standards for SSR, better known in the U. S. as the Air Traffic Control Radar Beacon System (ATCRBS); 2) provide specifications for 3-pulse sidelobe suppression (SLS); 3) provide standards for introduction of automatic height transmission; and 4) specify conditions under which SSR is to be implemented. It was agreed further that the sensing element of the system should use a standard pressure setting of 1013.2 millibars and that it would be necessary to refer to the system as height transmission rather than altitude reporting. Although a separate data link for height transmission is a possibility, the probable implementation data was considered too uncertain. Since air traffic is a heterogeneous mixture of civil and military aircraft, the existing SSR used by both civil and military aircraft was expanded to accommodate automatic height transmission features. It was agreed that SSR is needed to supplement the use of primary radar in air traffic control, but that each country would determine whether or not its use is required. The system specifications are appended to the paper.