885
Federal Aviation Administration, DOT
§ 171.315
(m)
False guidance.
False courses
which can be acquired and tracked by
an aircraft shall not exist anywhere ei-
ther inside or outside of the MLS cov-
erage sector. False courses which exist
outside of the minimum coverage sec-
tor may be suppressed by the use of
OCI.
N
OTE
: False courses may be due to (but not
limited to) MLS airborne receiver acquisi-
tion of the following types of false guidance:
reflections of the scanning beam, scanning
beam antenna sidelobes and grating lobes,
and incorrect clearance.
§ 171.315 Azimuth monitor system re-
quirements.
(a) The approach azimuth or back
azimuth monitor system must cause
the radiation to cease and a warning
must be provided at the designated
control point if any of the following
conditions persist for longer than the
periods specified:
(1) There is a change in the ground
equipment contribution to the mean
course error component such that the
path following error at the reference
datum or in the direction of any azi-
muth radial, exceeds the limits speci-
fied in §§ 171.313(e)(1) or 171.313(j) for a
period of more than one second.
N
OTE
: The above requirement and the re-
quirement to limit the ground equipment
mean error to
±
10 ft. can be satisfied by the
following procedure. The integral monitor
alarm limit should be set to the angular
equivalent of
±
10 ft. at the approach ref-
erence datum. This will limit the electrical
component of the mean course error to
±
10
ft. The field monitor alarm limit should be
set such that with the mean course error at
the alarm limit the total allowed PFE is not
exceeded on any commissioned approach
course from the limit of coverage to an alti-
tude of 100 feet.
(2) There are errors in two consecu-
tive transmissions of Basic Data Words
1, 2, 4 or 5.
(3) There is a reduction in the radi-
ated power to a level not less than that
specified in §§ 171.313(a)(4) or
171.313(g)(4) for a period of more than
one second.
(4) There is an error in the preamble
DPSK transmissions which occurs
more than once in any one second pe-
riod.
(5) There is an error in the time divi-
sion multiplex synchronization of a
particular azimuth function that the
requirement specified in § 171.311(e) is
not satisfied and if this condition per-
sists for more than one second.
(6) A failure of the monitor is de-
tected.
(b) Radiation of the following
fuctions must cease and a warning pro-
vided at the designated control point if
there are errors in 2 consecutive trans-
missions:
(1) Morse Code Identification,
(2) Basic Data Words 3 and 6,
(3) Auxiliary Data Words.
886
14 CFR Ch. I (1–1–24 Edition)
§ 171.317
(c) The period during which erro-
neous guidance information is radiated
must not exceed the periods specified
in § 171.315(a). If the fault is not cleared
within the time allowed, the ground
equipment must be shut down. After
shutdown, no attempt must be made to
restore service until a period of 20 sec-
onds has elapsed.
§ 171.317 Approach elevation perform-
ance requirements.
This section prescribes the perform-
ance requirements for the elevation
equipment components of the MLS as
follows:
(a)
Elevation coverage requirements.
The approach elevation facility must
provide proportional guidance informa-
tion in at least the following volume of
space (see Figure 13):
(1) Laterally within a sector origi-
nating at the datum point which is at
least equal to the proportional guid-
ance sector provided by the approach
azimuth ground equipment.
(2) Longitudinally from 75 meters (250
feet) from the datum point to 20 nau-
tical miles from threshold in the direc-
tion of the approach.
(3) Vertically within the sector
bounded by:
(i) A surface which is the locus of
points 2.5 meters (8 feet) above the run-
way surface;
(ii) A conical surface originating at
the datum point and inclined 0.9 degree
above the horizontal and,
(iii) A conical surface originating at
the datum point and inclined at 15.0 de-
grees above the horizontal up to a
height of 6000 meters (20,000 feet).