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Approach elevation guidance
–89.5 –88.0 –84.5 N/A N/A
N/A = not applicable
Note.— The table above specifies the minimum power densities for clearance signals and scanning beam signals. The
relative values of the two signals are specified in 3.11.4.6.2.5.2.
3.11.4.10.2 The power density of the approach azimuth angle guidance signals shall be greater than that specified in
3.11.4.10.1 by at least:
a) 15 dB at the approach reference datum;
Chapter 3 Annex 10 — Aeronautical Communications
3-89 23/11/06
b) 5 dB for one degree or 9 dB for 2 degree or larger beamwidth antennas at 2.5 m (8 ft) above the runway surface, at
the MLS datum point, or at the farthest point of the runway centre line which is in line of sight of the azimuth
antenna.
Note 1.— Near the runway surface the approach azimuth equipment will normally provide power densities higher than
those specified for angle signals in 3.11.4.10.1 to support auto-land operations. Attachment G provides guidance as regards
antenna beamwidth and power budget considerations.
Note 2.— The specifications for coverage in 3.11.5.2.2 and 3.11.5.3.2 make provision for difficult ground equipment
siting conditions in which it may not be feasible to provide the power density specified in 3.11.4.10.2.
3.11.5 Ground equipment characteristics
3.11.5.1 Synchronization and monitoring. The synchronization of the time-division-multiplexed angle guidance and
data transmissions which are listed in 3.11.4.3.3 shall be monitored.
Note.— Specific monitoring requirements for various MLS functions are specified in 3.11.5.2.3 and 3.11.5.3.3.
3.11.5.1.1 Residual radiation of MLS functions. The residual radiation of an MLS function at times when another
function is radiating shall be at least 70 dB below the level provided when transmitting.
Note.— The acceptable level of residual radiation for a particular function is that level which has no adverse effect on
the reception of any other function and is dependent upon equipment siting and aircraft position.
3.11.5.2 Azimuth guidance equipment
3.11.5.2.1 Scanning beam characteristics. Azimuth ground equipment antennas shall produce a fan-shaped beam
which is narrow in the horizontal plane, broad in the vertical plane and which is scanned horizontally between the limits of
the proportional guidance sector.
3.11.5.2.1.1 Coordinate system. Azimuth guidance information shall be radiated in either conical or planar coordinates.
3.11.5.2.1.2 Antenna beamwidth. The antenna beamwidth shall not exceed 4 degrees.
Note.— It is intended that the detected scanning beam envelope, throughout the coverage should not exceed
250 microseconds (equivalent to a beamwidth of 5 degrees) in order to ensure proper angle decoding by the airborne
equipment.
3.11.5.2.1.3 Scanning beam shape. The minus 10-dB points on the beam envelope shall be displaced from the beam
centre by at least 0.76 beamwidth, but not more than 0.96 beamwidth.
Note.— The beam shape described applies on boresight in a multipath free environment using a suitable filter.
Information on beam shape and side lobes is provided in Attachment G, 3.1 and 3.2.
3.11.5.2.2 Coverage
Note.— Diagrams illustrating the coverage requirements specified herein are contained in Attachment G, Figures G-5A,
G5-B and G-6.
3.11.5.2.2.1 Approach azimuth. The approach azimuth ground equipment shall provide guidance information in at least
the following volumes of space:
Annex 10 — Aeronautical Communications Volume I
23/11/06 3-90
3.11.5.2.2.1.1 Approach region.
a) Laterally, within a sector of 80 degrees (normally plus and minus 40 degrees about the antenna boresight) which
originates at the approach azimuth antenna phase centre.
b) Longitudinally, from the approach azimuth antenna to 41.7 km (22.5 NM).
c) Vertically, between:
1) a lower conical surface originating at the approach azimuth antenna phase centre and inclined upward to reach,
at the longitudinal coverage limit, a height of 600 m (2 000 ft) above the horizontal plane which contains the
antenna phase centre; and
2) an upper conical surface originating at the approach azimuth antenna phase centre inclined at 15 degrees above
the horizontal to a height of 6 000 m (20 000 ft).
Note 1.— Where intervening obstacles penetrate the lower surface, it is intended that guidance need not be provided at
less than line-of-sight heights.
Note 2.— Where it is determined that misleading guidance information exists outside the promulgated coverage sector
and appropriate operational procedures cannot provide an acceptable solution, techniques to minimize the effects are
available. These techniques include adjustment of the proportional guidance sector or use of out-of-coverage indication
　
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