Federal Aviation Administration, DOT

Section 171.111

(iii) The identification signal must
employ the International Morse Code
and consist of three letters.
(iv) The identification signal must be
transmitted at a speed corresponding
to approximately seven words per
minute, and must be repeated at approximately equal intervals, not less
than six times per minute. When SDF
transmission is not available for operational use, including periods of removal of navigational components or
during maintenance or test transmissions, the identification signal
must be suppressed.
(b) It must be shown during ground
inspection of the design features of the
equipment that there will not be conditions that will allow unsafe operations
because of component failure or deterioration.
(c) The monitor must be checked periodically during the in-service test
evaluation period for calibration and
stability. These tests, and ground
checks of SDF radiation characteristics must be conducted in accordance
with the maintenance manual required
by Section 171.115(c) and must meet the standards and tolerances contained in
Section 171.111(j).
(d) The monitor system must provide
a warning to the designated control
point(s) when any of the conditions of
Section 171.111(j) occur, within the time periods specified in that paragraph.
(e) Flight inspection to determine
the adequacy of the facility-s operational performance and compliance
with applicable performance requirements must be conducted in accordance with the  - U.S. Standard Flight
Inspection Manual. -  Tolerances contained in the U.S. Standard Flight Inspection Manual, section 217, must be
complied with except as stated in paragraph (f) of this section.
(f) Flight inspection tolerances specified in section 217 of the  - U.S. Standard Flight Inspection Manual -  must be
complied with except as follows:
(1) Course sector width. The nominal
course sector width must be 6Section. When
an operational advantage can be
achieved, a nominal course sector
width of 12Section may be established. Course
sector width must be adjusted and
maintained within the limits of Section17
percent of the nominal value.

(2) Course alignment. The mean course
line must be adjusted and maintained
within the limits of Section10 percent of the
nominal course sector width.
(3) Course structure. Course deviations
due to roughness, scalloping, or bends
must be within the following limitations:
(i) Front course. (a) Course structure
from 18 miles from runway threshold to
Point A must not exceed Section40 microamperes;
(b) Point A to Point A-1 - linear decrease from not more than Section40 microamperes at Point A to not more than
Section20 microamperes at Point A-1;
(c) Point A-1 to Missed Approach
Point - not more than Section20 microamperes;
(d) Monitor tolerances: width Section17 percent of nominal; alignment - Section10 percent of nominal course sector width.
(ii) Back course. (a) Course structure
18 miles from runway threshold to 4
miles from runway threshold must not
exceed Section40 microamperes. Four miles
to 1 mile from R/W must not exceed Section40
microamperes decreasing to not more
than Section20 microamperes, at a linear
rate.
(b) Monitor tolerances: width - Section17
percent of nominal; alignment - Section10
percent of nominal course sector width.
[Doc. No. 10116, 35 FR 12711, Aug. 11, 1970, as
amended by Amdt. 171-9, 38 FR 28557, Oct. 15,
1973]

Section 171.111 Ground standards and tolerances.
Compliance with this section must be
shown as a condition to approval and
must be maintained during operation
of the SDF.
(a) Frequency. (1) 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 tolerance of the radio frequency carrier must not exceed plus or
minus 0.002 percent.
(2) The modulating tones must be 90
Hz and 150 Hz within Section2.5 percent.
(3) The identification signal must be
1020 Hz within Section50 Hz.
(4) The total harmonic content of the
90 Hz tone must not exceed 10 percent.
(5) The total harmonic content of the
150 Hz tone must not exceed 10 percent.

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