872 

14 CFR Ch. I (1–1–19 Edition) 

§ 171.313 

used to provide the balance of the re-
quired coverage where the proportional 
sector is less than 

±

40 degrees. 

(2) Vertically in the runway region 

between: 

(i) A horizontal surface 2.5 meters (8 

feet) above the farthest point of run-
way 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 hori-
zontal up to a height of 600 meters (2000 
feet). 

(3) Vertically in the back azimuth re-

gion 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 de-
grees 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 den-
sities must not be less than those 
shown in Table 9, but the equipment 
design must also allow for: 

(i) Transmitter power degradation 

from normal 

¥

1.5 dB. 

(ii) Rain loss of 

¥

2.2 dB at the longi-

tudinal coverage extremes. 

(h) 

Back azimuth siting. 

The back azi-

muth equipment antenna must: 

(1) Normally be located on the exten-

sion 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 ref-
erence datum; 

(3) Have minimum height necessary 

to comply with the course require-
ments 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 ap-

proach 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 ei-
ther conical or planar. 

(j) 

Back azimuth accuracy. 

The re-

quirements specified in § 171.313(e) 
apply except that the reference point is 
the back azimuth reference datum. 

(k) 

Back azimuth antenna characteris-

tics. 

The requirements specified in 

§ 171.313(f) apply. 

(l) 

Scanning conventions. 

Figure 12 

shows the approach azimuth and back 
azimuth scanning conventions. 

VerDate Sep<11>2014 

08:20 May 17, 2019

Jkt 247048

PO 00000

Frm 00882

Fmt 8010

Sfmt 8010

Y:\SGML\247048.XXX

247048