700 

14 CFR Ch. I (1–1–19 Edition) 

§ 77.23 

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. 

(b) The purpose of an aeronautical 

study is to determine whether the 
aeronautical effects of the specific pro-
posal and, where appropriate, the cu-
mulative impact resulting from the 
proposed construction or alteration 
when combined with the effects of 
other existing or proposed structures, 
would constitute a hazard to air navi-
gation. 

(c) The obstruction standards in sub-

part C of this part are supplemented by 
other manuals and directives used in 
determining the effect on the navigable 
airspace of a proposed construction or 
alteration. When the FAA needs addi-
tional information, it may circulate a 
study to interested parties for com-
ment. 

§ 77.27

Initiation of studies. 

The FAA will conduct an aero-

nautical study when: 

(a) Requested by the sponsor of any 

proposed construction or alteration for 
which a notice is submitted; or 

(b) The FAA determines a study is 

necessary. 

§ 77.29

Evaluating aeronautical effect. 

(a) The FAA conducts an aero-

nautical study to determine the impact 
of a proposed structure, an existing 
structure that has not yet been studied 
by the FAA, or an alteration of an ex-
isting structure on aeronautical oper-
ations, procedures, and the safety of 
flight. These studies include evalu-
ating: 

(1) The impact on arrival, departure, 

and en route procedures for aircraft op-
erating under visual flight rules; 

(2) The impact on arrival, departure, 

and en route procedures for aircraft op-
erating under instrument flight rules; 

(3) The impact on existing and 

planned public use airports; 

(4) Airport traffic capacity of exist-

ing public use airports and public use 
airport development plans received be-
fore the issuance of the final deter-
mination; 

(5) Minimum obstacle clearance alti-

tudes, minimum instrument flight 
rules altitudes, approved or planned in-
strument approach procedures, and de-
parture procedures; 

(6) The potential effect on ATC radar, 

direction finders, ATC tower line-of- 

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