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made to determine an elevation antenna location. Siting criteria have been developed based on minimizing the effects of MLS
elevation equipment on the ILS glide path signal. This criteria along with signal-in-space, operational, critical areas, and
obstacle clearance considerations will influence the final location of the elevation antenna.
4.1.1.1.2 The purpose is to start with a general region for siting the elevation antenna and then to reduce this region
to an optimum location for a particular facility. This goal is achieved by stepping through a series of factors and
considerations. This decision-making process is shown as a logic flow diagram in Figure G-17. These guidelines are not
intended to be an all-inclusive MLS siting manual, but only to provide additional guidance when MLS collocation with
ILS is required.
4.1.1.1.3 Referring to Figure G-17, the section number corresponds to one of the three siting geometries, that is 4.1.1.2
for “siting the elevation antenna between the glide path and runway”, etc. The numbers in each block reference the specific
paragraph in the supporting text for Figure G-17. This paragraph provides a more detailed description of the factor(s) to be
considered for that step.
4.1.1.1.4 The two general regions for siting the elevation antenna are shown in Figure G-18. Depending on the location
of the glide path, either one region or the other may not exist. In addition, these regions must already satisfy signal-in-space
criteria prior to their consideration.
4.1.1.2 Siting the elevation antenna between the glide path and the runway
4.1.1.2.1 The setback for the elevation antenna is dependent upon the MLS approach reference datum (ARD) height.
The MLS ARD must satisfy the criteria stated in Chapter 3, 3.11.4.9.1. The elevation antenna setback can be determined by
the equation (see Figure G-19):
15
tan tan
SB ARDH RPCH RPCH
− −
= ≥
θ θ
ATT G-13 23/11/06
Annex 10 — Aeronautical Communications Volume I
Where:
all distances are in metres;
SB is the setback distance of the elevation antenna phase centre from the runway threshold, parallel to the runway centre line;
RPCH is the relative phase centre height of the elevation antenna compared to the runway surface at threshold. (This includes
the elevation antenna phase centre height and the difference in terrain elevation between the threshold and the elevation
antenna site.);
ARDH is the desired MLS approach reference datum height; and
θ is the minimum glide path.
4.1.1.2.2 The conical coordinate system of the elevation antenna and its offset from centre line will cause the minimum
glide path elevation guidance to be above the approach reference datum. Considering the recommendation of Chapter 3,
3.11.5.3.5.2.2 this offset should be limited by the following equation:
( ) ( ) ( ) 2
2 2 18
tan
RPCH
OS SB
⎡ − ⎤
+ ≤⎢⎣ θ ⎥⎦
Where:
all distances are in metres; and
OS is the offset distance between the elevation antenna phase centre and the vertical plane containing the runway centre line
(see Figure G-19).
4.1.1.2.3 Furthermore, the MLS ARD should be coincident with the ILS reference datum within one metre as stated in
Chapter 3, 3.11.5.3.5.3. This is given in the following equation:
1 1
tan tan
RDH RPCH SB RDH RPCH
− − + −
≤ ≤
θ θ
Where:
all distances are in metres; and
RDH is the height of the ILS reference datum.
4.1.1.2.4 To determine the diagonal boundary for Region 1 of Figure G-18 two factors need to be considered. The
first factor is that the elevation antenna must not penetrate the region through which the Fresnel zone for the ILS glide
path migrates during an approach. In general, this requirement can be achieved by siting the elevation antenna to the
runway side of the diagonal line between the glide path antenna mast and the runway centre line at threshold. The value
for φ in Figure G-18 is dependent on the location of the glide path antenna mast relative to centre line at threshold. The
second factor is to minimize lateral penetration of the glide path antenna pattern (see 4.1.1.3.2). However, for this
elevation antenna region satisfying the second factor is preferable but not essential.
4.1.1.2.5 After determining the acceptable range of elevation antenna locations based on the above criteria, the
minimum elevation antenna offset is determined by the obstacle limitation requirements in Annex 14, Chapter 4.
4.1.1.2.6 When possible the elevation antenna location is to be adjusted to minimize the effects of the elevation
antenna critical area on flight operations. Furthermore, it may be desirable to choose the elevation antenna location in a way
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