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(b) Back azimuth;
(c) Approach elevation;
(d) Range; and
(e) Data communications.
5. The standard configuration of MLS ground
equipment includes:
(a) An azimuth station to perform functions
(a) and (e) above. In addition to providing azimuth
navigation guidance, the station transmits basic data
which consists of information associated directly
with the operation of the landing system, as well as
advisory data on the performance of the ground
equipment.
(b) An elevation station to perform function
(c).
(c) Distance Measuring Equipment (DME) to
perform range guidance, both standard DME
(DME/N) and precision DME (DME/P).
6. MLS Expansion Capabilities. The standard
configuration can be expanded by adding one or
more of the following functions or characteristics.
(a) Back azimuth. Provides lateral guidance
for missed approach and departure navigation.
(b) Auxiliary data transmissions. Provides
additional data, including refined airborne positioning,
meteorological information, runway status, and
other supplementary information.
(c) Expanded Service Volume (ESV) proportional
guidance to 60 degrees.
7. MLS identification is a four−letter designation
starting with the letter M. It is transmitted in
International Morse Code at least six times per
minute by the approach azimuth (and back azimuth)
ground equipment.
b. Approach Azimuth Guidance
1. The azimuth station transmits MLS angle and
data on one of 200 channels within the frequency
range of 5031 to 5091 MHz.
2. The equipment is normally located about
1,000 feet beyond the stop end of the runway, but
there is considerable flexibility in selecting sites. For
example, for heliport operations the azimuth
transmitter can be collocated with the elevation
transmitter.
3. The azimuth coverage extends:
(See FIG 1−1−8.)
(a) Laterally, at least 40 degrees on either side
of the runway centerline in a standard configuration,
(b) In elevation, up to an angle of 15 degrees
and to at least 20,000 feet, and
(c) In range, to at least 20 NM.
AIM 2/19/04
1−1−14 Air Navigation Aids
FIG 1−1−8
Coverage Volume
Azimuth
APPROACH
AZIMUTH
AZIMUTH
-40°
+40°
20 NM
ESV
ESV
14 NM
MAXIMUM LIMIT +60°
14 NM
-60°
c. Elevation Guidance
1. The elevation station transmits signals on the
same frequency as the azimuth station. A single
frequency is time−shared between angle and data
functions.
2. The elevation transmitter is normally located
about 400 feet from the side of the runway between
runway threshold and the touchdown zone.
3. Elevation coverage is provided in the same
airspace as the azimuth guidance signals:
(a) In elevation, to at least +15 degrees;
(b) Laterally, to fill the Azimuth lateral
coverage; and
(c) In range, to at least 20 NM.
(See FIG 1−1−9.)
FIG 1−1−9
Coverage Volumes
Elevation
ELEVATION
NORMAL
GLIDE PATH
MAXIMUM LIMIT 20,000’
20 NM
30
3
15
o
o
o
o
d. Range Guidance
1. The MLS Precision Distance Measuring
Equipment (DME/P) functions the same as the
navigation DME described in paragraph 1−1−7,
Distance Measuring Equipment (DME), but there are
some technical differences. The beacon transponder
operates in the frequency band 962 to 1105 MHz and
responds to an aircraft interrogator. The MLS DME/P
accuracy is improved to be consistent with the
accuracy provided by the MLS azimuth and elevation
stations.
2. A DME/P channel is paired with the azimuth
and elevation channel. A complete listing of the
200 paired channels of the DME/P with the angle
functions is contained in FAA Standard 022 (MLS
Interoperability and Performance Requirements).
3. The DME/N or DME/P is an integral part of
the MLS and is installed at all MLS facilities unless
a waiver is obtained. This occurs infrequently and
only at outlying, low density airports where marker
beacons or compass locators are already in place.
e. Data Communications
1. The data transmission can include both the
basic and auxiliary data words. All MLS facilities
transmit basic data. Where needed, auxiliary data can
be transmitted.
2. Coverage limits. MLS data are transmitted
throughout the azimuth (and back azimuth when
provided) coverage sectors.
3. Basic data content. Representative data
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