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Federal Aviation Administration, DOT 

§ 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 

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