657
Federal Aviation Administration, DOT
§ 77.19
as landing and takeoff pathways. Those
determined pathways must be consid-
ered runways, and an appropriate pri-
mary surface as defined in § 77.19 will
be considered as longitudinally cen-
tered on each such runway. Each end of
that primary surface must coincide
with the corresponding end of that run-
way.
(e) The standards in this subpart
apply to construction or alteration
proposals on an airport (including heli-
ports and seaplane bases with marked
lanes) if that airport is one of the fol-
lowing before the issuance of the final
determination:
(1) Available for public use and is
listed in the Airport/Facility Direc-
tory, Supplement Alaska, or Supple-
ment Pacific of the U.S. Government
Flight Information Publications; or
(2) A planned or proposed airport or
an airport under construction of which
the FAA has received actual notice, ex-
cept DOD airports, where there is a
clear indication the airport will be
available for public use; or,
(3) An airport operated by a Federal
agency or the DOD; or,
(4) An airport that has at least one
FAA-approved instrument approach.
§ 77.17
Obstruction standards.
(a) An existing object, including a
mobile object, is, and a future object
would be an obstruction to air naviga-
tion if it is of greater height than any
of the following heights or surfaces:
(1) A height of 499 feet AGL at the
site of the object.
(2) A height that is 200 feet AGL, or
above the established airport ele-
vation, whichever is higher, within 3
nautical miles of the established ref-
erence point of an airport, excluding
heliports, with its longest runway
more than 3,200 feet in actual length,
and that height increases in the pro-
portion of 100 feet for each additional
nautical mile from the airport up to a
maximum of 499 feet.
(3) A height within a terminal obsta-
cle clearance area, including an initial
approach segment, a departure area,
and a circling approach area, which
would result in the vertical distance
between any point on the object and an
established minimum instrument
flight altitude within that area or seg-
ment to be less than the required ob-
stacle clearance.
(4) A height within an en route obsta-
cle clearance area, including turn and
termination areas, of a Federal Airway
or approved off-airway route, that
would increase the minimum obstacle
clearance altitude.
(5) The surface of a takeoff and land-
ing area of an airport or any imaginary
surface established under § 77.19, 77.21,
or 77.23. However, no part of the take-
off or landing area itself will be consid-
ered an obstruction.
(b) Except for traverse ways on or
near an airport with an operative
ground traffic control service furnished
by an airport traffic control tower or
by the airport management and coordi-
nated with the air traffic control serv-
ice, the standards of paragraph (a) of
this section apply to traverse ways
used or to be used for the passage of
mobile objects only after the heights of
these traverse ways are increased by:
(1) 17 feet for an Interstate Highway
that is part of the National System of
Military and Interstate Highways
where overcrossings are designed for a
minimum of 17 feet vertical distance.
(2) 15 feet for any other public road-
way.
(3) 10 feet or the height of the highest
mobile object that would normally tra-
verse the road, whichever is greater,
for a private road.
(4) 23 feet for a railroad.
(5) For a waterway or any other tra-
verse way not previously mentioned,
an amount equal to the height of the
highest mobile object that would nor-
mally traverse it.
§ 77.19
Civil airport imaginary sur-
faces.
The following civil airport imaginary
surfaces are established with relation
to the airport and to 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 ap-
proach surface applied to each end of a
runway are determined by the most
precise approach procedure existing or
planned for that runway end.
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14 CFR Ch. I (1–1–24 Edition)
§ 77.19
(a)
Horizontal surface. A horizontal
plane 150 feet above the established air-
port elevation, the perimeter of which
is constructed by swinging arcs of a
specified radii from the center of each
end of the primary surface of each run-
way 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 des-
ignated 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 ar-
ithmetical 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 extend-
ing outward and upward from the pe-
riphery of the horizontal surface at a
slope of 20 to 1 for a horizontal distance
of 4,000 feet.
(c)
Primary surface. A surface longitu-
dinally centered on a runway. When
the runway has a specially prepared
hard surface, the primary surface ex-
tends 200 feet beyond each end of that
runway; but when the runway has no
specially prepared 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 the primary surface is:
(1) 250 feet for utility runways having
only visual approaches.
(2) 500 feet for utility runways having
non-precision 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 non-precision instru-
ment runways having visibility mini-
mums greater than three-fourths stat-
ute mile.
(iii) 1,000 feet for a non-precision in-
strument runway having a non-preci-
sion instrument approach with visi-
bility minimums as low as three-
fourths of a statute mile, and for preci-
sion instrument runways.
(iv) The width of the primary surface
of a runway will be that width pre-
scribed in this section for the most pre-
cise approach existing or planned for
either end of that runway.
(d)
Approach surface. A surface longi-
tudinally centered on the extended
runway centerline and extending out-
ward 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 avail-
able or planned for that runway end.
(1) The inner edge of the approach
surface is the same width as the pri-
mary 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 non-precision instru-
ment approach;
(iv) 3,500 feet for that end of a non-
precision instrument runway other
than utility, having visibility mini-
mums greater that three-fourths of a
statute mile;
(v) 4,000 feet for that end of a non-
precision instrument runway, other
than utility, having a non-precision in-
strument approach with visibility
minimums as low as three-fourths stat-
ute mile; and
(vi) 16,000 feet for precision instru-
ment 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 non-precision instrument runways
other than utility; and
(iii) 10,000 feet at a slope of 50 to 1
with an additional 40,000 feet at a slope
of 40 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 sub-
section for the most precise approach
existing or planned for that runway
end.
(e)
Transitional surface. These sur-
faces extend outward and upward at
right angles to the runway centerline
and the runway centerline extended at
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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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