Section 171.259

14 CFR Ch. I (1-1-19 Edition)

208 V nominal value, 177 V to 239 V (Section2 V).*
240 V nominal value, 204 V to 276 V (Section0.2
V).*
AC line frequency (60 Hz), 57 Hz to 63 Hz
(Section0.2 Hz).*
DC voltage (48 V), 44 V to 52 V (Section0.5 V).*
* NOTE: Where discrete values of the above
frequency or voltages are specified for testing purposes, the tolerances given in parentheses indicated by an asterisk apply to the
test instruments used to measure these parameters.
Elevation, 0 to 10,000 ft. above sea level.
Duty, continuous, unattended.

(2) Ambient conditions for localizer
and glide path equipment:
Temperature, Section10 SectionC to + 50 SectionC.
Relative humidity, 5% to 90%.

(3) Ambient conditions for marker
beacon facilities and all other equipment installed outdoors (for example,
antennae, field detectors, and shelters):
Temperature, Section50 SectionC. to + 70 SectionC.
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 falling 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 accordance 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 distance from the threshold, similar instrumental indications in the aircraft
represent similar displacements from
the course line or ISMLS glide path, as
appropriate, regardless of the particular ground installation in use.
(2) The localizer and glide path components 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 requirements specified in Section 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 frequency plan approved by the FAA, and
must meet the following signal format
requirements:
(1) The localizer and glide slope stations 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 averaging over several beam scans, is
equivalent to the modulation used for
conventional ILS as specified in subpart C of this part, except that the frequency tolerance may not exceed
Section0.0001 percent.
(2) Guidance modulation must be impressed on the microwave carrier of the
radiated signal in the form of a summation of 90 Hz and 150 Hz sinusoidal
modulation corresponding to the pointing direction of the particular beam
which radiates the signal.
(3) Each of the effective beam positions must be illuminated in a particular sequence for a short time interval. The modulation impressed on each
beam must be a sample of the combined 90 Hz and 150 Hz waveform appropriate for that particular beam direction and time slot, and must be accomplished by appropriately varying the
length of time the carrier is radiated
during each beam illumination interval.
(4) For those cases where the scanning 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 guidance sector. In the clearance region,
the step may not exceed 0.8 times the
beam width.
(5) At least one pulse duration modulation (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.

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