The document describes the components and operation of an Microwave Landing System (MLS), which provides precision guidance for aircraft approaches and landings. Key points include: - MLS uses antennas to scan microwave beams that an aircraft's receiver uses to calculate its position and guidance information. - MLS provides azimuth, elevation, distance, back azimuth and data communication capabilities to pilots for all-weather precision approaches and landings. - The system includes azimuth and elevation stations to provide lateral and vertical guidance, along with Distance Measuring Equipment for accurate distance information. - MLS is capable of Category III precision approaches and landings with very low decision heights or no decision height at all. It can guide aircraft along the

2.  ground-based instrument approach system
that provides precision guidance to an
aircraft approaching a runway, using a
combination of radio signals and, in many
cases, high-intensity lighting arrays

3.  Localizer
 Glideslope

4.  Provides lateral guidance
 LOC (LZZ in Europe)
 Facility indication by periodically transmitting a 1020 Hz
morse code identification signal
 Directional

5.  Glidepath (GP)
 sited to one side of the runway touchdown zone
 signal is transmitted on a carrier frequency between
329.15 and 335 MHz using a technique similar to that of
the localizer
 centerline of the glideslope signal is arranged to define
a glideslope of approximately 3° above horizontal
(ground level)

7.  activates an indicator on the pilot's
instrument panel and the tone of the beacon
is audible to the pilot
 Outer, Middle, Inner

8.  located 7.2 km (3.9 NM) from the threshold
 Morse-style dashes of a 400 Hz tone
 blue lamp that flashes in unison with the received audio code
 provide height, distance and equipment functioning checks to
aircraft on intermediate and final approach

9.  ideally at a distance of approximately 3,500 ft (1,100 m) from the
threshold
 modulated with a 1300 Hz tone as alternating dots and dashes
at the rate of two per second
 amber lamp that flashes in unison with the received audio code

10.  Ideally at a distance of approximately 100 ft (30 m) from the
threshold
 Morse-style dots at 3000 Hz
 white lamp that flashes in unison with the received audio code

11.  Distance Measuring Equipment
 provides pilots with a slant range measurement of
distance to the runway in nautical miles
 provides more accurate and continuous monitoring of
correct progress on the ILS glideslope to the pilot, and
does not require an installation outside the airport
boundary

12.  assess the vital characteristics of the transmissions
 medium or high intensity
 assists the pilot in transitioning from instrument to visual
flight, and to align the aircraft visually with the runway
centerline

13.  Category I
 Category II
 Category III
› A
› B
› C

14.  A precision instrument approach and landing with a
decision height not lower than 200 feet (61 m) above
touchdown zone elevation and with either a visibility not
less than 800 meters (2,625 ft) or a runway visual range
not less than 550 meters (1,804 ft)

15.  A precision instrument approach and landing
with a decision height lower than 200 feet
(61 m) above touchdown zone elevation but
not lower than 100 feet (30 m), and a runway
visual range not less than 350 meters
(1,148 ft)

16.  a decision height lower than 100 feet (30 m) above touchdown
zone elevation, or no decision height
 a runway visual range not less than 200 meters (656 ft)
 a decision height lower than 50 feet (15 m) above touchdown zone
elevation, or no decision height
 a runway visual range less than 200 meters (656 ft) but not less
than 50 meters (164 ft)

17.  A precision instrument approach and landing with no decision
height and no runway visual range limitations
 capable of using an aircraft's autopilot to land the aircraft and can
also provide guidance along the runway surface

19.  all-weather, precision landing system
originally intended to replace or supplement
the Instrument Landing System (ILS)
 provides azimuth, elevation, and distance, as
well as "back azimuth"
 used for short-range communications with
airport controllers

20.  MLS employs 5GHz transmitters at the
landing place which use passive
electronically scanned rays to send scanning
beams towards approaching aircraft. An
aircraft that enters the scanned volume uses
a special receiver that calculates its position
by measuring the arrival times of the beams.

21.  wide selection of channels to avoid interference
with other nearby airports
 excellent performance in all weather
 small "footprint" at the airports

22.  antennas were much smaller
 did not have to be placed at a specific point
at the airport
 signals covered a very wide fan-shaped area
off the end of the runway
 uses a single frequency, broadcasting the
azimuth and altitude information one after
the other

23.  Approach azimuth
 Back azimuth
 Approach elevation
 Range communications
 Data communications

24.  analogous to ILS localizer but has a proportionally wider
coverage
 transmits MLS angle and data
 located 1000 ft beyond the end of the runway
 coverage is reliable up to 20 nm from runway threshold
and 20000ft of height
 laterally 40° on either side of the runway centerline
 frequency Range of 5031-5091 MHz

25. Coverage volume of the
Azimuth station
Volumes of the elevation station
 The azimuth coverage extends: Laterally, at least 40 degrees on
either side of the runway centerline in a standard configuration. In
elevation, up to an angle of 15 degrees and to at least 20,000 feet
(6 km), and in range, to at least 20 nautical miles (37 km)

26.  provides lateral guidance for missed approach and departure
navigation
 operates on the same frequency as approach azimuth but at a
different time in the transmission sequence
 An MLS azimuth guidance station with rectangular azimuth
scanning antenna with DME antenna at left

27.  transmits signals on the same frequency as the azimuth station
 located 400 ft from the side of the runway between runway
threshold and touchdown zone
 elevation to at least 15°
 An MLS elevation guidance station

28.  provided by the precision Distance Measuring
Equipment (DME, DME/P)
 provides continuous and highly accurate distance
information

29.  can include both the basic and auxiliary data words
 MLS data are transmitted throughout the azimuth (and
back azimuth when provided) coverage sectors

30.  Representative data
› Station identification
 four-letter
designation starting
with the letter M
› Exact locations of
azimuth elevation and
DME/P stations (for
MLS receiver
processing functions)
› Ground equipment
performance level
› DME/P channel and
status
 Auxiliary data content
› 3-D locations of MLS
equipment
› Waypoint coordinates
› Runway conditions and
Weather (e.g., RVR,
ceiling, altimeter setting,
wind, wake vortex, wind
shear)