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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. 

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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).