831 

Federal Aviation Administration, DOT 

§ 171.113 

(b) 

Power output. 

The normal carrier 

power output must be of a value which 
will provide coverage requirements of 
§ 171.109(a)(6) when reduced by 3 dB to 
the monitor RF power reduction alarm 
point specified in § 171.111(j)(3). 

(c) 

VSWR. 

(1) The VSWR of carrier 

and sideband feedlines must be a nomi-
nal value of 1/1 and must not exceed 1.2/ 
1. 

(2) The sponsor will also provide addi-

tional manufacturer’s ground stand-
ards and tolerances for all VSWR pa-
rameters peculiar to the equipment 
which can effect performance of the fa-
cility in meeting the requirements 
specified in §§ 171.109 and 171.111. 

(d) 

Insulation resistance. 

The insula-

tion resistance of all coaxial feedlines 
must be greater than 20 megohms. 

(e) 

Depth of modulation. 

(1) The depth 

of modulation of the radio frequency 
carrier due to each of the 90 Hz and 150 
Hz tones must be 20 percent 

±

2 percent 

along the course line. 

(2) The depth of modulation of the 

radio frequency carrier due to the 1020 
Hz identification signal must be within 
5 percent to 15 percent. 

(f) 

Course sector width. 

The standard 

course sector width must be 6

° 

or 12

°

. 

The course sector must be maintained 
with 

±

17 percent of the standard. 

(g) 

Course alignment. 

Course align-

ment must be as specified in 
§ 171.109(a)(8). 

(h) 

Back course alignment and width. 

If 

a back course is provided, standards 
and tolerances for back course sector 
width and alignment must be the same 
as course sector width and course 
alignment specified in paragraphs (f) 
and (g) of this section. 

(i) 

Clearance. 

Clearance must be as 

specified in § 171.109(a)(10). 

(j) 

Monitor standards and tolerances. 

(1) The monitor system must provide a 
warning to the designated control 
point(s) when any of the conditions de-
scribed in this paragraph occur, within 
the time periods specified in paragraph 
(j)(6) of this section. 

(2) Course shift alarm: The monitor 

must alarm and cause radiation to 
cease, or identification and navigation 
signals must be removed, if the course 
alignment deviates from standard 
alignment by 10 percent or more of the 
standard course sector width. 

(3) RF power reduction alarm: The 

monitor must alarm and cause radi-
ation to cease, or identification and 
navigation signals must be removed, if 
the output power is reduced by 3 db or 
more from normal. 

(4) Modulation level alarm: The mon-

itor must alarm and cause radiation to 
cease, or identification and navigation 
signals must be removed, if the 90 Hz 
and 150 Hz modulation levels decrease 
by 17 percent or more. 

(5) Course sector width alarm: The 

monitor must alarm and cause radi-
ation to cease, or identification and 
navigation signals must be removed, 
for a change in course sector width to 
a value differing by 

±

17 percent or more 

from the standard. 

(6) Monitor delay before shutdown: 

Radiation must cease, or identification 
and navigation signals must be re-
moved, within 10 seconds after a fault 
is detected by the monitor, and no at-
tempt must be made to resume radi-
ation for a period of at least 20 seconds. 
If an automatic recycle device is used, 
not more than three successive recy-
cles may be permitted before a com-
plete SDF shutdown occurs. 

(k) 

Mean time between failures. 

The 

mean time between failures must not 
be less than 800 hours. This measure is 
applied only to equipment failures 
(monitor or transmitting equipment, 
including out of tolerance conditions) 
which result in facility shutdown. It 
does not relate to the responsiveness of 
the maintenance organization. 

(l) 

Course alignment stability. 

Drift of 

the course alignment must not exceed 
one-half the monitor limit in a 1-week 
period. 

[Doc. No. 10116, 35 FR 12711, Aug. 11, 1970, as 
amended by Amdt. 171–9, 38 FR 28558, Oct. 15, 
1973] 

§ 171.113 Installation requirements. 

(a) The facility must be installed ac-

cording to accepted good engineering 
practices, applicable electric and safe-
ty codes, and FCC requirements. 

(b) The SDF facility must have the 

following basic components: 

(1) VHF SDF equipment and associ-

ated monitor system; 

(2) Remote control, and indicator 

equipment (remote monitor) when re-
quired by the FAA; 

832 

14 CFR Ch. I (1–1–24 Edition) 

§ 171.115 

(3) A final approach fix; and 
(4) Compass locator (COMLO) or 

marker if suitable fixes and initial ap-
proach routes are not available from 
existing facilities. 

(c) The facility must have a reliable 

source of suitable primary power, ei-
ther from a power distribution system 
or locally generated. Also, adequate 
power capacity must be provided for 
operation of test and working equip-
ment at the SDF. A determination by 
the Federal Aviation Administration 
as to whether a facility will be required 
to have standby power for the SDF and 
monitor accessories to supplement the 
primary power will be made for each 
airport based upon operational mini-
mums and density of air traffic. 

(d) A determination by the Federal 

Aviation Administration as to whether 
a facility will be required to have dual 
transmitting equipment with auto-
matic changeover for the SDF will be 
made for each airport based upon oper-
ational minimums and density of air 
traffic. 

(e) There must be a means for deter-

mining, from the ground, the perform-
ance of the equipment (including an-
tennae), initially and periodically. 

(f) The facility must have the fol-

lowing ground-air or landline commu-
nication services: 

(1) At facilities outside of and not im-

mediately adjacent to controlled air-
space, there must be ground-air com-
munications from the airport served by 
the facility. The utilization of voice on 
the SDF should be determined by the 
facility operator on an individual basis. 

(2) At facilities within or imme-

diately adjacent to controlled airspace, 
there must be ground/air communica-
tions required by paragraph (b)(1) of 
this section and reliable communica-
tions (at least a landline telephone) 
from the airport to the nearest Federal 
Aviation Administration air traffic 
control or communications facility. 

Compliance with paragraphs (f) (1) and 
(2) of this section need not be shown at 
airports where an adjacent Federal 
Aviation Administration facility can 
communicate with aircraft on the 
ground at the airport and during the 
entire proposed instrument approach 
procedure. In addition, at low traffic 
density airports within or immediately 

adjacent to controlled airspace, and 
where extensive delays are not a fac-
tor, the requirements of paragraphs (f) 
(1) and (2) of this section may be re-
duced to reliable communications (at 
least a landline telephone) from the 
airport to the nearest Federal Aviation 
Administration air traffic control or 
communications facility, if an adjacent 
Federal Aviation Administration facil-
ity can communicate with aircraft dur-
ing the proposed instrument approach 
procedure down to the airport surface 
or at least down to the minimum ap-
proach altitude. 

(g) At those locations where two sep-

arate SDF facilities serve opposite 
ends of a single runway, an interlock 
must insure that only the facility serv-
ing the approach direction in use can 
radiate, except where no operationally 
harmful interference results. 

(h) At those locations where, in order 

to alleviate frequency congestion, the 
SDF facilities serving opposite ends of 
one runway employ identical fre-
quencies, an interlock must insure that 
the facility not in operational use can-
not radiate. 

(i) Provisions for maintenance and 

operations by authorized persons only. 

(j) Where an operational advantage 

exists, the installation may omit a 
back course. 

[Doc. No. 10116, 35 FR 12711, Aug. 11, 1970, as 
amended by Amdt. 171–16, 56 FR 65664, Dec. 
17, 1991] 

§ 171.115 Maintenance and operations 

requirements. 

(a) The owner of the facility shall es-

tablish an adequate maintenance sys-
tem and provide qualified maintenance 
personnel to maintain the facility at 
the level attained at the time it was 
commissioned. Each person who main-
tains a facility shall meet at a min-
imum the Federal Communications 
Commission’s licensing requirements 
and show that he has the special 
knowledge and skills needed to main-
tain the facility, including proficiency 
in maintenance procedures and the use 
of specialized test equipment. 

(b) The SDF must be designed and 

maintained so that the probability of 
operation within the performance re-
quirements specified is high enough to 
insure an adequate level of safety. In