Section 171.313

14 CFR Ch. I (1-1-19 Edition)

used to provide the balance of the required coverage where the proportional
sector is less than Section40 degrees.
(2) Vertically in the runway region
between:
(i) A horizontal surface 2.5 meters (8
feet) above the farthest point of runway centerline which is in line of sight
of the azimuth antenna, and,
(ii) A conical surface originating at
the azimuth ground equipment antenna
inclined at 20 degrees above the horizontal up to a height of 600 meters (2000
feet).
(3) Vertically in the back azimuth region between:
(i) A conical surface originating 2.5
meters (8 feet) above the runway stop
end, included at 0.9 degree above the
horizontal, and,
(ii) A conical surface orginating at
the missed approach azimuth ground
equipment antenna, inclined at 15 degrees above the horizontal up to a
height of 1500 meters (5000 feet).
(iii) Where obstacles penetrate the
lower coverage limits, coverage need be
provided only to minimum line of
sight.
(4) Within the back azimuth coverage
sector defined in paragraph (q) (1), (2),
and (3) of this section the power densities must not be less than those
shown in Table 9, but the equipment
design must also allow for:
(i) Transmitter power degradation
from normal Section1.5 dB.

(ii) Rain loss of Section2.2 dB at the longitudinal coverage extremes.
(h) Back azimuth siting. The back azimuth equipment antenna must:
(1) Normally be located on the extension of the runway centerline at the
threshold end;
(2) Be adjusted so that the vertical
plane containing the zero degree course
line contains the back azimuth reference datum;
(3) Have minimum height necessary
to comply with the course requirements prescribed in paragraph (g) of
this section;
(4) Be located at a distance from the
threshold end that is consistent with
safe obstruction clearance practices;
(5) Not obscure any light of an approach lighting system; and
(6) Be installed on frangible mounts
or beyond the 300 meter (1000 feet) light
bar.
(i) Back azimuth antenna coordinates.
The scanning beams transmitted by
the back azimuth equipment may be either conical or planar.
(j) Back azimuth accuracy. The requirements specified in Section 171.313(e)
apply except that the reference point is
the back azimuth reference datum.
(k) Back azimuth antenna characteristics. The requirements specified in
Section 171.313(f) apply.
(l) Scanning conventions. Figure 12
shows the approach azimuth and back
azimuth scanning conventions.

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