830
14 CFR Ch. I (1–1–24 Edition)
§ 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 ap-
proximately equal intervals, not less
than six times per minute. When SDF
transmission is not available for oper-
ational use, including periods of re-
moval of navigational components or
during maintenance or test trans-
missions, 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 condi-
tions that will allow unsafe operations
because of component failure or dete-
rioration.
(c) The monitor must be checked pe-
riodically during the in-service test
evaluation period for calibration and
stability. These tests, and ground
checks of SDF radiation characteris-
tics must be conducted in accordance
with the maintenance manual required
by § 171.115(c) and must meet the stand-
ards and tolerances contained in
§ 171.111(j).
(d) The monitor system must provide
a warning to the designated control
point(s) when any of the conditions of
§ 171.111(j) occur, within the time peri-
ods specified in that paragraph.
(e) Flight inspection to determine
the adequacy of the facility’s oper-
ational performance and compliance
with applicable performance require-
ments must be conducted in accord-
ance with the ‘‘U.S. Standard Flight
Inspection Manual.’’ Tolerances con-
tained in the U.S. Standard Flight In-
spection Manual, section 217, must be
complied with except as stated in para-
graph (f) of this section.
(f) Flight inspection tolerances speci-
fied in section 217 of the ‘‘U.S. Stand-
ard Flight Inspection Manual’’ must be
complied with except as follows:
(1)
Course sector width.
The nominal
course sector width must be 6
°
. When
an operational advantage can be
achieved, a nominal course sector
width of 12
°
may be established. Course
sector width must be adjusted and
maintained within the limits of
±
17
percent of the nominal value.
(2)
Course alignment.
The mean course
line must be adjusted and maintained
within the limits of
±
10 percent of the
nominal course sector width.
(3)
Course structure.
Course deviations
due to roughness, scalloping, or bends
must be within the following limita-
tions:
(i)
Front course.
(
a
) Course structure
from 18 miles from runway threshold to
Point A must not exceed
±
40 micro-
amperes;
(
b
) Point A to Point A–1—linear de-
crease from not more than
±
40 micro-
amperes at Point A to not more than
±
20 microamperes at Point A–1;
(
c
) Point A–1 to Missed Approach
Point—not more than
±
20 micro-
amperes;
(
d
) Monitor tolerances: width
±
17 per-
cent of nominal; alignment—
±
10 per-
cent 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
±
40 microamperes. Four miles
to 1 mile from R/W must not exceed
±
40
microamperes decreasing to not more
than
±
20 microamperes, at a linear
rate.
(
b
) Monitor tolerances: width—
±
17
percent of nominal; alignment—
±
10
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]
§ 171.111 Ground standards and toler-
ances.
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 oper-
ate on odd tenths or odd tenths plus a
twentieth MHz within the frequency
band 108.1 MHz to 111.95 MHz. The fre-
quency tolerance of the radio fre-
quency carrier must not exceed plus or
minus 0.002 percent.
(2) The modulating tones must be 90
Hz and 150 Hz within
±
2.5 percent.
(3) The identification signal must be
1020 Hz within
±
50 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.
