Recent growth in air-traffic movements is causing severe traffic congestion problems in terminal areas and en route. To meet these demands for more effective and safe utilization of airspace, separation standards in an air-traffic-control environment are being studied by the Review of the General Concept of Separation Panel (RGCSP) of the International Civil Aviation Organization.

One of the most effective ways of evaluating separation standards would be a mathematical method using a collision-risk model, for which we require data on the navigation accuracy of current aircraft as one of the parameters. At present, the data on navigation accuracy in the vertical dimension (height-keeping error) do not permit us to derive any definite conclusions on the distribution of navigational errors. In order to survey height-keeping errors we have developed a simple height-finding radar system, the Navigation Accuracy Measurement System (NAMS), based on a curve-fitting method. Thanks to this principle, NAMS has an advantage in its comparatively lower cost and simple structure.

The system consists of an antenna whose radiation pattern is a fan beam, a transceiver, a digitizer and a mini-computer. The antenna rotates about a horizontal axis and scans aircraft flying overhead. The height of an aircraft is estimated by processing the data obtained over several scans, using a mini-computer. This paper first outlines the characteristics of NAMS and then gives results of evaluation tests on its accuracy.