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Federal Aviation Administration, DOT
§ 171.107
§ 171.101 Scope.
This subpart sets forth minimum re-
quirements for the approval and oper-
ation of non-Federal Simplified Direc-
tional Facilities (SDF) that are to be
involved in the approval of instrument
flight rules and air traffic control pro-
cedures related to those facilities.
§ 171.103 Requests for IFR procedure.
(a) Each person who requests an IFR
procedure based on an SDF that he
owns must submit the following infor-
mation with that request:
(1) A description of the facility and
evidence that the equipment meets the
performance requirements of § 171.109
and the standards and tolerances of
§ 171.111, and is installed in accordance
with § 171.113.
(2) A proposed procedure for oper-
ating the facility.
(3) A proposed maintenance organiza-
tion and a maintenance manual that
meets the requirements of § 171.115.
(4) A statement of intent to meet the
requirements of this subpart.
(5) A showing that the facility has an
acceptable level of operational reli-
ability as prescribed in § 171.111(k), and
an acceptable standard of performance.
Previous equivalent operational experi-
ence with a facility with identical de-
sign and operational characteristics
will be considered in showing compli-
ance with this paragraph.
(b) After the Federal Aviation Ad-
ministration inspects and evaluates
the facility, it advises the owner of the
results and of any required changes in
the facility or the maintenance manual
or maintenance organization. The
owner must then correct the defi-
ciencies, if any, and operate the facil-
ity for an in-service evaluation by the
Federal Aviation Administration.
§ 171.105 Minimum requirements for
approval.
(a) The following are the minimum
requirements that must be met before
the Federal Aviation Administration
will approve an IFR procedure for a
non-Federal Simplified Directional Fa-
cility:
(1) A suitable frequency channel
must be available.
(2) The facility’s performance, as de-
termined by air and ground inspection,
must meet the requirements of
§§ 171.109 and 171.111.
(3) The installation of the equipment
must meet the requirements of
§ 171.113.
(4) The owner must agree to operate
and maintain the facility in accord-
ance with § 171.115.
(5) The owner must agree to furnish
periodic reports as set forth in § 171.117,
and agree to allow the FAA to inspect
the facility and its operation whenever
necessary.
(6) The owner must assure the FAA
that he will not withdraw the facility
from service without the permission of
the FAA.
(7) The owner must bear all costs of
meeting the requirements of this sec-
tion and of any flight or ground inspec-
tions made before the facility is com-
missioned, except that the FAA may
bear certain of these costs subject to
budgetary limitations and policy estab-
lished by the Administrator.
(b) If the applicant for approval
meets the requirements of paragraph
(a) of this section, the FAA commis-
sions the facility as a prerequisite to
its approval for use in an IFR proce-
dure. The approval is withdrawn at any
time the facility does not continue to
meet those requirements. In addition,
the facility is licensed by the Federal
Communications Commission. The
Federal Aviation Administration rec-
ommends cancellation or nonrenewal
of the Federal Communications Com-
mission license whenever the frequency
channel is needed for higher priority
common system service.
§ 171.107 Definition.
As used in this subpart:
SDF
(simplified directional facility)
means a directional aid facility pro-
viding only lateral guidance (front or
back course) for approach from a final
approach fix.
DDM
(difference in depth of modula-
tion) means the percentage modulation
depth of the larger signal minus the
percentage modulation depth of the
smaller signal, divided by 100.
Angular displacement sensitivity
means
the ratio of measured DDM to the cor-
responding angular displacement from
the appropriate reference line.
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14 CFR Ch. I (1–1–24 Edition)
§ 171.109
Back course sector
means the course
sector on the opposite end of the run-
way from the front course sector.
Course line
means the locus of points
along the final approach course at
which the DDM is zero.
Course sector
means a sector in a hori-
zontal plane containing the course line
and limited by the loci of points near-
est to the course line at which the
DDM is 0.155.
Displacement sensitivity
means the
ratio of measured DDM to the cor-
responding lateral displacement from
the appropriate reference line.
Front course sector
means the course
sector centered on the course line in
the direction from the runway in which
a normal final approach is made.
Half course sector
means the sector in
a horizontal plane containing the
course line and limited by the loci of
points nearest to the course line, at
which the DDM is 0.0775.
Point A
means a point on the front
course in the approach direction a dis-
tance of 4 nautical miles from the
threshold.
Point A1
means a point on the front
course in the approach direction a dis-
tance of 1 statute mile from the thresh-
old.
Point A2
means a point on the front
course at the threshold.
Reference datum
means a point at a
specified height located vertically
above the intersection of the course
and the threshold.
Missed approach point
means the
point on the final approach course, not
farther from the final approach fix
than Point ‘‘A2’’, at which the ap-
proach must be abandoned, if the ap-
proach and subsequent landing cannot
be safely completed by visual ref-
erence, whether or not the aircraft has
descended to the minimum descent al-
titude.
§ 171.109 Performance requirements.
(a) The Simplified Directional Facil-
ity must perform in accordance with
the following standards and practices:
(1) The radiation from the SDF an-
tenna system must produce a com-
posite field pattern which is amplitude
modulated by a 90 Hz and a 150 Hz tone.
The radiation field pattern must
produce a course sector with the 90 Hz
tone predominating on one side of the
course and with the 150 Hz tone pre-
dominating on the opposite side.
(2) When an observer faces the SDF
from the approach end of runway, the
depth of modulation of the radio fre-
quency carrier due to the 150 Hz tone
must predominate on his right hand
and that due to the 90 Hz tone must
predominate on his left hand.
(3) All horizontal angles employed in
specifying the SDF field patterns must
originate from the center of the an-
tenna system which provides the sig-
nals used in the front course sector.
(4) The SDF must operate on odd
tenths or odd tenths plus a twentieth
MHz within the frequency band 108.1
MHz to 111.95 MHz. The frequency tol-
erance of the radio frequency carrier
must not exceed plus or minus 0.002
percent.
(5) The radiated emission from the
SDF must be horizontally polarized.
The vertically polarized component of
the radiation on the course line must
not exceed that which corresponds to
an error one-twentieth of the course
sector width when an aircraft is posi-
tioned on the course line and is in a
roll attitude of 20
°
from the horizontal.
(6) The SDF must provide signals suf-
ficient to allow satisfactory operation
of a typical aircraft installation within
the sector which extends from the cen-
ter of the SDF antenna system to dis-
tances of 18 nautical miles within a
plus or minus 10
°
sector and 10 nautical
miles within the remainder of the cov-
erage when alternative navigational fa-
cilities provide satisfactory coverage
within the intermediate approach area.
SDF signals must be receivable at the
distances specified at and above a
height of 1,000 feet above the elevation
of the threshold, or the lowest altitude
authorized for transition, whichever is
higher. Such signals must be receiv-
able, to the distances specified, up to a
surface extending outward from the
SDF antenna and inclined at 7
°
above
the horizontal.
(7) The modulation tones must be
phase-locked so that within the half
course sector, the demodulated 90 Hz
and 150 Hz wave forms pass through
zero in the same direction within 20
°
of
phase relative to the 150 Hz component,
every half cycle of the combined 90 Hz