842
14 CFR Ch. I (1–1–24 Edition)
§ 171.255
§ 171.255 Requests for IFR procedures.
(a) Each person who requests an IFR
procedure based on an ISMLS facility
that he owns must submit the fol-
lowing information with that request:
(1) A description of the facility and
evidence that the equipment meets the
performance requirements of §§ 171.259,
171.261, 171.263, 171.265, 171.267, and
171.269, and is installed in accordance
with § 171.271.
(2) A proposed procedure for oper-
ating the facility.
(3) A proposed maintenance organiza-
tion and a maintenance manual that
meets the requirements of § 171.273.
(4) A statement of intent to meet the
requirements of this subpart.
(5) A showing that the ISMLS facil-
ity has an acceptable level of oper-
ational reliability, maintainability and
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 FAA inspects and evalu-
ates the ISMLS facility, it advises the
owner of the results and of any re-
quired changes in the ISMLS facility
or in the maintenance manual or main-
tenance organization. The owner must
then correct the deficiencies, if any,
and operate the ISMLS facility for an
inservice evaluation by the FAA.
§ 171.257 Minimum requirements for
approval.
(a) The following are the minimum
requirements that must be met before
the FAA approves an IFR procedure for
a non-Federal ISMLS facility:
(1) The performance of the ISMLS fa-
cility, as determined by flight and
ground inspection conducted by the
FAA, must meet the requirements of
§§ 171.259, 171.261, 171.263, 171.265, 171.267,
and 171.269.
(2) The installation of the equipment
must meet the requirements of
§ 171.271.
(3) The owner must agree to operate
and maintain the ISMLS facility in ac-
cordance with § 171.273.
(4) The owner must agree to furnish
periodic reports as set forth in § 171.275
and agree to allow the FAA to inspect
the facility and its operation whenever
necessary.
(5) The owner must assure the FAA
that he will not withdraw the ISMLS
facility from service without the per-
mission of the FAA.
(6) The owner must bear all costs of
meeting the requirements of this sec-
tion and of any flight or ground inspec-
tion made before the ISMLS facility is
commissioned, except that the FAA
may bear certain costs subject to budg-
etary 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 approves
the ISMLS facility for use in an IFR
procedure. The approval is withdrawn
at any time that the ISMLS facility
does not continue to meet those re-
quirements. In addition, the ISMLS fa-
cility may be de-commissioned when-
ever the frequency channel is needed
for higher priority common system
service.
§ 171.259 Performance requirements:
General.
(a) The ISMLS consists of the fol-
lowing basic components:
(1) C-Band (5000 MHz–5030 MHz) local-
izer equipment, associated monitor
system, and remote indicator equip-
ment;
(2) C-Band (5220 MHz–5250 MHz) glide
path equipment, associated monitor
system, and remote indicator equip-
ment;
(3) VHF marker beacons (75 MHz), as-
sociated monitor systems, and remote
indicator equipment.
(4) An ISMLS airborne receiver or a
VHF/UHF ILS receiver modified to be
capable of receiving the ISMLS signals.
This modification requires the addition
of a C-Band antenna, a converter unit,
a microwave/ILS mode control, and a
VHF/UHF receiver modification kit.
(b) The electronic ground equipments
in paragraph (a)(1), (2), and (3) of this
section, must be designed to operate on
a nominal 120/240 volt, 60 Hz, 3-wire sin-
gle phase AC power source.
(c) ISMLS ground equipment must
meet the following service conditions:
(1) AC line parameters, DC voltage,
elevation, and duty:
120 V nominal value, 102 V to 138 V (
±
1 V).*
843
Federal Aviation Administration, DOT
§ 171.259
208 V nominal value, 177 V to 239 V (
±
2 V).*
240 V nominal value, 204 V to 276 V (
±
0.2
V).*
AC line frequency (60 Hz), 57 Hz to 63 Hz
(
±
0.2 Hz).*
DC voltage (48 V), 44 V to 52 V (
±
0.5 V).*
* N
OTE
: Where discrete values of the above
frequency or voltages are specified for test-
ing purposes, the tolerances given in paren-
theses indicated by an asterisk apply to the
test instruments used to measure these pa-
rameters.
Elevation, 0 to 10,000 ft. above sea level.
Duty, continuous, unattended.
(2) Ambient conditions for localizer
and glide path equipment:
Temperature,
¥
10
°
C to + 50
°
C.
Relative humidity, 5% to 90%.
(3) Ambient conditions for marker
beacon facilities and all other equip-
ment installed outdoors (for example,
antennae, field detectors, and shelters):
Temperature,
¥
50
°
C. to + 70
°
C.
Relative humidity, 5% to 100%.
(4) All equipment installed outdoors
must operate satisfactorily under the
following conditions:
Wind velocity, 0–100 MPH (not including
gusts).
Hail stones,
1
⁄
2
″
diameter.
Rain, provide coverage through a distance
of 5 nautical miles with rain falling at a rate
of 50 millimeters per hour, and with rain fall-
ing at the rate of 25 millimeters per hour for
the additional design performance range of
the system.
Ice loading, encased in
1
⁄
2
″
radial thickness
of clear ice.
(d) The ISMLS must perform in ac-
cordance with the following standards
and practices for Facility Performance
Category I operation:
(1) The ISMLS must be constructed
and adjusted so that, at a specified dis-
tance from the threshold, similar in-
strumental indications in the aircraft
represent similar displacements from
the course line or ISMLS glide path, as
appropriate, regardless of the par-
ticular ground installation in use.
(2) The localizer and glide path com-
ponents listed in paragraphs (a)(1) and
(a)(2) of this section which form part of
an ISMLS, must comply at least with
the standard performance requirements
specified herein. The marker beacon
components listed in paragraph (a)(3)
of this section which form part of an
ISMLS, must comply at least with the
standard performance requirements
specified in subpart H of this part.
(3) The ISMLS must be so designed
and maintained that the probability of
operation is within the performance re-
quirements specified in § 171.273(k).
(e) The signal format and pairing of
the runway localizer and glide path
transmitter frequencies of an ISMLS
must be in accordance with the fre-
quency plan approved by the FAA, and
must meet the following signal format
requirements:
(1) The localizer and glide slope sta-
tions must transmit angular guidance
information on a C-band microwave
carrier on narrow, scanned antenna
beams that are encoded to produce a
modulation in space which, after aver-
aging over several beam scans, is
equivalent to the modulation used for
conventional ILS as specified in sub-
part C of this part, except that the fre-
quency tolerance may not exceed
±
0.0001 percent.
(2) Guidance modulation must be im-
pressed on the microwave carrier of the
radiated signal in the form of a sum-
mation of 90 Hz and 150 Hz sinusoidal
modulation corresponding to the point-
ing direction of the particular beam
which radiates the signal.
(3) Each of the effective beam posi-
tions must be illuminated in a par-
ticular sequence for a short time inter-
val. The modulation impressed on each
beam must be a sample of the com-
bined 90 Hz and 150 Hz waveform appro-
priate for that particular beam direc-
tion and time slot, and must be accom-
plished by appropriately varying the
length of time the carrier is radiated
during each beam illumination inter-
val.
(4) For those cases where the scan-
ning beam fills the coverage space in
steps, the incremental step must not
exceed 0.6 times the beam width where
the beam is in the proportional guid-
ance sector. In the clearance region,
the step may not exceed 0.8 times the
beam width.
(5) At least one pulse duration modu-
lation (pdm) sample pulse per beam
width of scan must be provided.
(6) The minimum pulse duration
must be 40 microseconds.
(7) The minimum beam scan cycle
must be 600 Hz.
844
14 CFR Ch. I (1–1–24 Edition)
§ 171.261
(8) The minimum duty ratio detect-
able by a receiver located anywhere in
the coverage areas defined by this spec-
ification may not be less than 0.1. De-
tected duty ratio means the ratio of
the average energy per scan detected at
a point in space to the average energy
per scan transmitted in all directions
through the transmitting antenna.
(9) The localizer must produce a C-
band unmodulated reference frequency
signal of sufficient strength to allow
satisfactory operation of an aircraft re-
ceiver within the specified localizer
and glide path coverage sectors. Pair-
ing of this reference frequency with the
localizer and glide slope frequencies
must be in accordance with a frequency
plan approved by the FAA.
§ 171.261 Localizer performance re-
quirements.
This section prescribes the perform-
ance requirements for localizer equip-
ment components of the ISMLS.
(a) The localizer antenna system
must:
(1) Be located on the extension of the
centerline of the runway at the stop
end;
(2) Be adjusted so that the course line
be on a vertical plane containing the
centerline of the runway served;
(3) Have the minimum height nec-
essary to comply with the coverage re-
quirements prescribed in paragraph (j)
of this section;
(4) Be located at a distance from the
stop end of the runway that is con-
sistent with safe obstruction clearance
practices;
(5) Not obscure any light of the ap-
proach landing system; and
(6) Be installed on frangible mounts
or beyond the 1000
′
light bar.
(b) On runways where limited terrain
prevents the localizer antennae from
being positioned on the runway center-
line extended, and the cost of the land
fill or a tall tower antenna support is
prohibitive, the localizer antenna array
may be offset, including a collocated
ground station, so that the course
intercepts the centerline at a point de-
termined by the amount of the angular
offset and the glide path angle. If other
than a runway centerline localizer is
used, the criteria in subpart C of part
97 of this chapter is applicable.
(c) At locations where two separate
ISMLS facilities serve opposite ends of
of a single runway, an interlock must
ensure that only the facility serving
the approach direction being used will
radiate.
(d) The radiation from the localizer
antenna system must produce a com-
posite field pattern which is pulse du-
ration modulated, the time average
equivalent to amplitude modulation by
a 90 Hz and 150 Hz tone. The localizer
station must transmit angular guid-
ance information over a C-band micro-
wave carrier on narrow, scanned an-
tenna beams that are encoded to
produce a modulation in space which,
after averaging over several beam
scans, is equivalent to the modulation
used for conventional ILS as specified
in subpart C of this part. The radiation
field pattern must produce a course
sector with one tone predominating on
one side of the course and with the
other tone predominating on the oppo-
site side. When an observer faces the
localizer from the approach end of the
runway, the depth of modulation of the
radio frequency 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.
(e) All horizontal angles employed in
specifying the localizer field patterns
must originate from the center of the
localizer antenna system which pro-
vides the signals used in the front
course sector.
(f) The ISMLS course sector angle
must be adjustable between 3 degrees
and 9 degrees. The applicable course
sector angle will be established and ap-
proved on an individual basis.
(g) The ISMLS localizer must operate
in the band 5000 MHz to 5030 MHz. The
frequency tolerance may not exceed
±
0.0001 percent.
(h) The emission from the localizer
must be vertically polarized. The hori-
zontally polarized component of the ra-
diation of the course line may not ex-
ceed that which corresponds to a DDM
error of 0.016 when an aircraft is posi-
tioned on the course line and is in a
roll attitude of 20 degrees from the hor-
izontal.
(i) The localizer must provide signals
sufficient to allow satisfactory oper-
ation of a typical aircraft installation