659
Federal Aviation Administration, DOT
§ 77.25
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 preci-
sion 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.
§ 77.21
Department of Defense (DOD)
airport imaginary surfaces.
(a)
Related to airport reference points.
These surfaces apply to all military
airports. For the purposes of this sec-
tion, a military airport is any airport
operated by the DOD.
(1)
Inner horizontal surface. A plane
that is oval in shape at a height of 150
feet above the established airfield ele-
vation. 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 extend-
ing from the periphery of the inner
horizontal surface outward and upward
at a slope of 20 to 1 for a horizontal dis-
tance of 7,000 feet to a height of 500 feet
above the established airfield ele-
vation.
(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 pre-
vious lateral clearance criteria, the
2,000-foot width may be reduced to the
former criteria.
(2)
Clear zone surface. A surface lo-
cated 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 in-
clined 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 clear-
ance surface is 50 to 1 along the runway
centerline extended until it reaches an
elevation of 500 feet above the estab-
lished airport elevation. It then con-
tinues horizontally at this elevation to
a point 50,000 feet from the point of be-
ginning. The width of this surface at
the runway end is the same as the pri-
mary surface, it flares uniformly, and
the width at 50,000 is 16,000 feet.
(4)
Transitional surfaces. These sur-
faces 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 out-
ward and upward at right angles to the
runway centerline.
§ 77.23
Heliport imaginary surfaces.
(a)
Primary surface. The area of the
primary surface coincides in size and
shape with the designated take-off and
landing area. This surface is a hori-
zontal plane at the elevation of the es-
tablished heliport elevation.
(b)
Approach surface. The approach
surface begins at each end of the heli-
port primary surface with the same
width as the primary surface, and ex-
tends outward and upward for a hori-
zontal distance of 4,000 feet where its
width is 500 feet. The slope of the ap-
proach surface is 8 to 1 for civil heli-
ports and 10 to 1 for military heliports.
(c)
Transitional surfaces. These sur-
faces extend outward and upward from
the lateral boundaries of the 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.
Subpart D—Aeronautical Studies
and Determinations
§ 77.25
Applicability.
(a) This subpart applies to any aero-
nautical study of a proposed construc-
tion or alteration for which notice to
the FAA is required under § 77.9.
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