875 

Federal Aviation Administration, DOT 

§ 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). 

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