A surface longitudinally centered on a runway. The elevation of any point on the Primary Surface is the same as the elevation of the nearest point on the runway centerline.
Tangents then connect the adjacent arcs.
For PIR and Non-Precision Instrument Runways, the radius of each arc is 10,000 feet. The radius of the arcs specified for each end of a runway will have the same numerical value, that value being the highest determined for either end of the runway. When a 5,000 foot arc is encompassing by tangents connecting two adjacent 10,000 foot arcs, it shall be disregarded. A PIR Approach Surface that project beyond the limits of the Conical Surface extends a distance of 5,000 feet measured horizontally from the edge of the Approach Surface. The surface width is that of the Primary Surface at the beginning and increases uniformly to a width of 16,000 feet at a distance of 50,000 feet from the end of the Primary Surface.