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considering the specific approach profile and airport environment.
4.3.8 Elevation. The elevation critical area to be protected results from the critical volume shown in Figure G-24.
Normally no sensitive area is defined for the elevation antenna. As the lower surface of the critical volume normally is well
ATT G-21 23/11/06
Annex 10 — Aeronautical Communications Volume I
above ground level, aircraft may hold near the elevation antenna as long as the lower boundary of the critical volume is not
penetrated.
4.3.8.1 For normal siting of a 1.0 degree beamwidth elevation antenna and flat ground, the fuselage of most aircraft
types will fit under the profile lower surface of the critical volume of Figure G-24.
4.3.8.2 For a 1.5 degree beamwidth elevation antenna, limited penetration of the profile lower surface of the critical
volume of Figure G-24 by an aircraft fuselage may be tolerated by defining the lower part of the critical volume between
1.5 degrees and 1.7 beamwidth below the minimum glide path as sensitive volume. At sites performing well within tolerance,
aircraft may hold in front of the antenna provided:
a) the separation angle between the glide path and the top of the aircraft fuselage is at least 1.5 degrees;
b) the aircraft tail fin does not penetrate the lower surface of the critical volume; and
c) the fuselage is at right angle to the centre line.
4.3.8.3 For MLS/RNAV approach procedures, the plan view of the elevation critical area will require expansion to
ensure the elevation signal quality along the nominal approach track (Figure G-28). These expanded areas protect approach
procedures which are not possible with ILS. The characteristics of the profile view (Figure G-24) remain unchanged, noting
that the lower boundary is referenced to the nominal approach track. This guidance material covers a wide range of profiles.
Increased flexibility may be obtained by performing an analysis considering the specific approach profile and airport
environment.
5. Operational considerations on siting of DME ground equipment
5.1 The DME equipment should, whenever possible, provide indicated zero range to the pilot at the touchdown point in
order to satisfy current operational requirements.
5.1.1 When DME/P is installed with the MLS, indicated zero range referenced to the MLS datum point may be
obtained by airborne equipment utilizing coordinate information from the MLS data. DME zero range should be referenced
to the DME/P site.
6. Interrelationship of ground equipment monitor and control actions
6.1 The interrelationship of monitor and control actions is considered necessary to ensure that aircraft do not receive
incomplete guidance which could jeopardize safety, but at the same time continue to receive valid guidance which may
safely be utilized in the event of certain functions ceasing to radiate.
Note.— The interrelationship of ground equipment monitor and control actions is presented in Table G-14.
7. Airborne equipment
7.1 General
7.1.1 The airborne equipment parameters and tolerances included in this section are intended to enable an
interpretation of the Standards contained in Chapter 3, 3.11 and include allowances, where appropriate, for:
23/11/06 ATT G-22
Attachment G Annex 10 — Aeronautical Communications
a) variation of the ground equipment parameters within the limits defined in Chapter 3, 3.11;
b) aircraft manoeuvres, speeds and attitudes normally encountered within the coverage volume.
Note 1.— The airborne equipment includes the aircraft antenna(s), the airborne receiver, the pilot interface equipment
and the necessary interconnections.
Note 2.— Detailed “Minimum Performance Specifications” for MLS avionics have been compiled and coordinated by
the European Organization for Civil Aviation Electronics (EUROCAE) and RTCA Inc. ICAO periodically provides to
Contracting States current lists of the publications of these organizations in accordance with Recommendations 3/18(a)
and 6/7(a) of the Seventh Air Navigation Conference.
7.1.2 Function decoding
7.1.2.1 The airborne equipment is to be capable of decoding and processing the approach azimuth, high rate approach
azimuth, back azimuth, and approach elevation functions, and data required for the intended operation.
7.1.2.2 In addition, the receiver utilizes techniques to prevent function processing resulting from the presence of
function preambles embedded within the data fields of basic and auxiliary data words and scanning beam side lobe radiation.
One technique to accomplish this is to decode all function preambles. Following the decode of a preamble, the detection and
decoding of all function preambles is then disabled for a period of time corresponding to the length of the function.
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