AIM
4/3/14
1−1−14
Navigation Aids
f.
The SDF signal is fixed at either 6 degrees or
12 degrees as necessary to provide maximum
flyability and optimum course quality.
g.
Identification consists of a three−letter identifi-
er transmitted in Morse Code on the SDF frequency.
The appropriate instrument approach chart will
indicate the identifier used at a particular airport.
1
−
1
−
11. Microwave Landing System (MLS)
a. General
1.
The MLS provides precision navigation
guidance for exact alignment and descent of aircraft
on approach to a runway. It provides azimuth,
elevation, and distance.
2.
Both lateral and vertical guidance may be
displayed on conventional course deviation indicat-
ors or incorporated into multipurpose cockpit
displays. Range information can be displayed by
conventional DME indicators and also incorporated
into multipurpose displays.
3.
The MLS supplements the ILS as the standard
landing system in the U.S. for civil, military, and
international civil aviation. At international airports,
ILS service is protected to 2010.
4.
The system may be divided into five
functions:
(a)
Approach azimuth;
(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 func-
tion (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 stand-
ard 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 position-
ing, meteorological information, runway status, and
other supplementary information.
(c)
Expanded Service Volume (ESV) propor-
tional guidance to 60 degrees.
7.
MLS identification is a four−letter designa-
tion 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.