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area will fall within the runway boundaries such that adequate control can be exercised over all moving traffic to prevent
unacceptable interference to the MLS signals. In developing the sensitive area lengths of Table G-12A it was assumed that
the landed B-727 (or B-747) type aircraft has cleared the runway before the landing aircraft reaches a height of 90 m (300 ft)
(or 180 m (600 ft) for B-747)). That assumption resulted from consideration of the following factors:
a) 5.6 km (3 NM) separation behind B-747 size aircraft;
b) 3.7 km (2 NM) separation behind B-727 size aircraft;
c) runway occupancy time for the landing aircraft is 30 seconds; and
d) approaching aircraft speed is approximately 220 km/hr (2 NM/min).
4.3.7.1 For an azimuth antenna supporting an offset approach the critical and sensitive areas will depend on the
azimuth antenna location and the approach track orientation relative to the zero degree azimuth. The critical area extends for
at least 300 m (1 000 ft) in front of the azimuth antenna. To avoid shadowing while landing operations are in progress,
additional protection is to be provided in the form of a sensitive area. Table G-12B gives sensitive area length for use with an
23/11/06 ATT G-20
Attachment G Annex 10 — Aeronautical Communications
offset azimuth installation. When a procedure is along an azimuth other than the zero degree azimuth, the plan view
definition has to take into account beam spreading. Figure G-25 shows typical examples.
Note.— This guidance material also applies to an azimuth antenna providing the back azimuth function.
4.3.7.2 Critical and sensitive areas for the computed centre line approach. Figure G-26 provides a general illustration
of the areas to be protected from uncontrolled movement of ground traffic. The exact shape of that area will depend on the
azimuth antenna location, azimuth to threshold distance, decision height, type of aircraft operating at the facility, and the
multipath environment.
4.3.7.2.1 In determining the area to be protected, the following steps are appropriate:
a) determine the direction of line AG (Figure G-26) from the azimuth antenna (point A) to the nearest point to the
runway centre line where guidance is required (point G);
b) locate point C on line AG at a distance from the azimuth antenna found by entering Table G-12C or G-12D with
azimuth to threshold distance, size of the largest aircraft on ground and height of point G on the minimum glide
path;
c) line AB has the same length as line AC and lines AC and AB are angularly separated by an amount for in-beam
multipath (1.7 beamwidth) and a value for flight path deviation allowance to account for deviations of the
approaching aircraft about the nominal approach track;
d) determine the direction of line AF from the azimuth antenna to point F at a height of 300 m (1 000 ft) on the
minimum glide path;
e) determine the direction of line AD which is angularly separated by 1.7 BW from line AF;
f) the length of line AD is taken from Table G-12C or G-12D with information on the height of point F; and
g) the area to be protected is bounded by the polygon ABCD.
4.3.7.2.2 Typically the areas of polygon ABCD in Figure G-26 within at least the first 300 m (1 000 ft) or 600 m
(2 000 ft) of the azimuth antenna are to be designated, respectively, as a critical area where B-727 or B-747 size aircraft are
operating. The balance of the region is designated as a sensitive area. Where possible, the azimuth antenna is to be offset to
the runway side away from that of active taxiways. At facilities where the azimuth antenna is set back less than 300 m
(1 000 ft) or located ahead of the runway stop end, a detailed analysis and consideration of the airport layout may support
reductions of the area to be protected.
4.3.7.3 Critical and sensitive areas for MLS/RNAV procedures. For MLS/RNAV approach procedures, the critical and
sensitive areas will require expansion to protect against in-beam multipath in the sectors used. These expanded areas protect
approach procedures which are not possible with ILS. The length of the area to be protected depends on the operational
minimum height surface selected from Table G-13. Information for determining the area to be protected is given in
Figure G-27. For a wide range of profiles, simulation indicated that, where B-727 size aircraft are operating, adequate
protection would be afforded if the first 300 m (1 000 ft) of the protected area is designated as a critical area and the
remainder as a sensitive area. For B-747 size aircraft, the corresponding length is 600 m (2 000 ft). For higher approach
profiles, the length derived from Table G-13 or an equation therein may be less than these values; in this case the entire
expanded area is to be designated as a critical area. Increased flexibility may be obtained by performing an analysis
　
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