The following civil airport imaginary surfaces are established with relation to the airport and each runway. The size of each such imaginary surface is based on the category of each runway according to the type of approach available or planned for that runway. The slope and dimensions of the approach surface applied to each end of a runway are determined by the most precise approach existing or planned for that runway end.

(a)

Horizontal surface - a horizontal plane 150 feet above the established airport elevation, the perimeter of which is constructed by swinging arcs of specified radii from the center of each end of the primary surface of each runway of each airport and connecting the adjacent arcs by lines tangent to those arcs. The radius of each arc is:

(1)

5,000 feet for all runways designated as utility or visual;

(2)

10,000 feet for all other runways. The radius of the arc specified for each end of a runway will have the same arithmetical value. That value will be the highest determined for either end of the runway. When a 5,000-foot arc is encompassed by tangents connecting two adjacent 10,000-foot arcs, the 5,000-foot arc shall be disregarded on the construction of the perimeter of the horizontal surface.

(b)

Conical surface - a surface extending outward and upward from the periphery of the horizontal surface at a slope of 20 to 1 for a horizontal distance of 4,000 feet.

(c)

Primary surface - a surface longitudinally centered on a runway. When the runway has a specially prepared hard surface, the primary surface extends 200 feet beyond each end of that runway but when the runway has no specially prepared hard surface, or planned hard surface, the primary surface ends at each end of that runway. The elevation of any point on the primary surface is the same as the elevation of the nearest point on the runway centerline. The width of a primary surface is:

(1)

250 feet for utility runways having only visual approaches.

(2)

500 feet for utility runways having nonprecision instrument approaches.

(3)

For other than utility runways the width is:

(i)

500 feet for visual runways having only visual approaches.

(ii)

500 feet for nonprecision instrument runways having visibility minimums greater than three-fourths [of a] statute mile.

(iii)

1,000 feet for a nonprecision instrument approach with visibility minimums as low as three-fourths of a statute mile, and for precision instrument runways.

The width of the primary surface of a runway will be that width prescribed in this section for the most precise approach existing or planned for either end of that runway.

(d)

Approach surface - a surface longitudinally centered on the extended runway centerline and extending outward and upward from each end of the primary surface. An approach surface is applied to each end of each runway based upon the type of approach available or planned for that runway end.

(1)

The inner edge of the approach surface is the same width as the primary surface and it expands uniformly to a width of:

(i)

1,250 feet for that end of a utility runway with only visual approaches;

(ii)

1,500 feet for that end of a runway other than a utility runway with only visual approaches;

(iii)

2,000 feet for that end of a utility runway with a nonprecision instrument approach;

(iv)

3,500 feet for that end of a nonprecision instrument runway other than utility, having visibility minimums greater than three-fourths of a statute mile;

(v)

4,000 feet for that end of a nonprecision instrument runway, other than utility, having a nonprecision instrument approach with visibility minimums as low as three-fourths [of a] statute mile; and

(vi)

16,000 feet for precision instrument runways.

(2)

The approach surface extends for a horizontal distance of:

(i)

5,000 feet at a slope of 20 to 1 for all utility and visual runways;

(ii)

10,000 feet at a slope of 34 to 1 for all nonprecision instrument runways other than utility; and

(iii)

10,000 feet at a slope of 50 to 1 for all precision instrument runways.

(3)

The outer width of an approach surface to an end of a runway will be that width prescribed in this subsection for the most precise approach existing or planned for that runway end.

(e)

Transitional surface - these surfaces extend outward and upward at right angles to the runway centerline extended at a slope of 7 to 1 from the sides of the primary surface and from the sides of the approach surfaces. Transitional surfaces for those portions of the precision approach surface which project through and beyond the limits of the conical surface, extend a distance of 5,000 feet measured horizontally from the edge of the approach surface and at right angles to the runway centerline.

(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 election. The plane is constructed by scribing an are with a radius of 7,500 feet about the centerline at the end of each runway and interconnecting these arcs with tangents.

(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 airports:

(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 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 feet.

(4)

Transitional surfaces. These surfaces connect the primary surfaces, the first 200 feet [of] 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 runway centerline.

(a)

Heliport primary surface. The area of the primary surface coincides in size and shape with the designated takeoff and landing area of a heliport. This surface is a horizontal plane at the elevation of the established heliport elevation.

(b)

Heliport approach surface. The approach surface begins at each end of the heliport primary surface with the same width as the primary surface, and extends outward and upward for a horizontal distance of 4,000 feet where its width is 500 feet. The slope of the approach surface is 8 to 1 for civil heliports and 10 to 1 for military heliports.

(c)

Heliport transitional surfaces. These surfaces extend outward and upward from the lateral boundaries of the heliport primary surface and from the approach surfaces at a slope of 2 to 1 for a distance of 250 feet measured horizontally from the centerline of the primary and approach surfaces.