(a) Related to airport reference points. These surfaces apply to
all military airports. For the purposes of this section a military airport
is any airport operated by an armed force of the United States.
(1) Inner horizontal surface. A plane is oval in shape at a
height of 150 feet above the established airfield elevation. The plane is
constructed by scribing an arc with a radius of 7,500 feet about the
centerline at the end of each runway and interconnecting these arcs with
(2) Conical surface. A surface extending from the periphery of
the inner horizontal surface outward and upward at a slope of 20 to 1 for
a horizontal distance of 7,000 feet to a height of 500 feet above the
established airfield elevation.
(3) Outer horizontal surface. A plane, located 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.
(b) Related to runways. These surfaces apply to all military
(1) Primary surface. A surface located on the ground or water
longitudinally centered on each runway with 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 in
accordance with a previous lateral clearance criteria, the 2,000-foot
width may be reduced to the former criteria.
(2) Clear zone surface. A surface located on the ground or water
at each end of the primary surface, with a length of 1,000 feet and the
same width as the primary surface.
(3) Approach clearance surface. An inclined plane, symmetrical
about the runway centerline extended, 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 to 1 along the runway centerline 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, it flares uniformly, and the width at 50,000 is 16,000
(4) Transitional surfaces. These surfaces connect the primary
surfaces, the first 200 feet of the clear zone surfaces, and the approach
clearance surfaces to the inner horizontal surface, conical surface, outer
horizontal surface or other transitional surfaces. The slope of the
transitional surface is 7 to 1 outward and upward at right angles to the