An inner horizontal surface is an oval plane that is at a height 150 feet above the
established airfield elevation. The plane is constructed by scribing an arc with a radius of
7,500 feet at the centerline at the end of each runway. The arcs are then interconnected
with tangents.
A conical surface is a surface extending from the periphery of the inner horizontal surface
outward and upward at a slope of 20:1. The horizontal distance is 7,000 feet, with a
height of 500 feet above the established airfield elevation.
An outer horizontal surface is a plane, 500 feet above the established airfield elevation,
extending outward from the outer periphery of the conical surface for a horizontal
distance of 30,000 feet.
(2) Related to Runways.
A primary surface may be located on the ground or the water. The primary surface is
longitudinally centered on each runway and is the same length as the runway. The width
of the primary surface for runways is 2,000 feet; however, at established bases where
substantial construction has taken place according to previous lateral-clearance criteria,
the 2,000-foot width may be reduced to the former criteria.
A clear-zone surface may be located on the ground or on water at each end of the primary
surface. The length is 1,000 feet, and the width is the same as the primary surface.
An approach/departure-clearance surface is an inclined plane, symmetrical at the
extended runway centerline, beginning 200 feet beyond each end of the primary surface
at the centerline elevation of the runway end and extending for 50,000 feet. The slope of
the approach-clearance surface is 50:1 along the runway-centerline and extended until it
reaches an elevation of 500 feet above the established airport elevation. It then continues
horizontally at this elevation to a point 50,000 feet from the point of beginning. The
width of this surface at the runway end is the same as the primary surface, then it flares
uniformly and the width at 50,000 feet is 16,000 feet.
A transitional surface connects the primary surfaces, the first 200 feet of the clear-zone
surfaces, and the approach/departure-clearance surfaces to the inner horizontal surface,
the conical surface, the outer horizontal surface, or other transitional surfaces. The slope
of the transitional surface is 7:1 outward and upward at right angles to the runway
centerline.
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EN0593
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