[Code of Federal Regulations]
[Title 14, Volume 2]
[Revised as of January 1, 2008]
From the U.S. Government Printing Office via GPO Access
[CITE: 14CFR77.28]

[Page 491-492]
 
                     TITLE 14--AERONAUTICS AND SPACE
 
CHAPTER I--FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION 
                               (CONTINUED)
 
PART 77_OBJECTS AFFECTING NAVIGABLE AIRSPACE--Table of Contents
 
                     Subpart C_Obstruction Standards
 
Sec. 77.28  Military airport imaginary surfaces.

    (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 
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 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

[[Page 492]]

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 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 runway centerline.

[Doc. No. 1882, 30 FR 1839, Feb. 10, 1965, as amended by Amdt. 77-1, 30 
FR 6713, May 18, 1965; Amdt. 77-9, 36 FR 5971, Apr. 1, 1971]