ILS paperwork air traffic control

Instrument Landing System (ILS) Case Study

Table of contents
Contents
Acknowledgement… ……………………………………………………………..

I

1.0: Introduction and Its History………………...………………………..…….

1

2.0: Instrumentation…………….....……………………………………..............

1

3.0: Instrument Landing System (ILS)...….…………….………………………

5

3.1: Equipment ………………………………………..............................

6

3.1.1: Equipment’s for Ground Installations……………………

6

3.1.2: Equipment’s for Airborne…………………………………

6

3.2: Component……………………………………………………………

7

3.2.1: Localizer…………………………………………………….
3.2.1.1: Localizer Back course……………………………

7
8

3.2.2: Glide Path…………………………………………………..

9

4.0 Marker Beacon………………………………………………………………..

10

4.1 Outer Maker…………………………………………………………..

11

4.2 Middle Maker…………………………………………………………

12

4.3 Inner Maker…………………………………………………………..

12

5.0: Monitoring of ILS…….………………………………………………….…

13

6.0: Approach Lighting………………………………………………..................

14

7.0: ILS Categories……………………………………………………………….

15
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7.1: Categories….…………………………………………………

15

7.1.1 CAT 1………………………………………………..

15

7.1.2 CAT 2………………………………………………..

15

7.1.3 CAT 3(a)……………………………………………..

15

7.1.4 CAT 3(b)…………………………………………….

16

7.1.5 CAT 3(c)…………………………………………….

16

8.0: ILS Critical Area…………………………………………………………….

18

8.1 Snow Removal………………………………………………..

20

9.0: ILS System Work……………………………………………………………

23

9.1: Individual Part………………………………………………

24

10.0: Rate of Decent Formula…………………………………………………….

25

11.0: Benefits of ILS………………………………………………………………

26

11.1 Disadvantages of ILS……………………………………….

27

12.0: Future Development………………………………………………………

27

13.0: Conclusion………………………………………………………………….

28

14.0: Bibliography………………………………………………………………..

29

1.0 Introduction and Its History
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Instrument Landing System is landing navigational Aids that are used widely in airlines and
it also using radio waves to transmit signal.Radio isthe transmission and reception of radio
waves, especially those carrying audio messages.Navigation is the process of plan and directs
the route of aircraft by using instruments or maps.Aircraft Communication is the delivery of
information to or from aircraft by radio or signals1.Air Navigation is the action of plotting
and directing the route of an aircraft through theair from one place to another2.
One of the most difficult tasks a pilot has to perform is to achieve a smooth and safe landing.
Early pilots landed on an open field, facing any direction that gave them the best angle
relative to the wind. But as traffic grew and more aircraft began to use airports rather than
farms or fields, landings became limited to certain directions. Landing aids were developed to
help pilots find the correct landing course and to make landing safer.
Airports had begun using lights in the late 1920s, when landing fields were marked with
rotating lights so they could be found after dark. In the early 1930s, airports installed the
earliest forms of approach lighting. These indicated the correct angle of descent and whether
the pilot was right on target. Their approach path was called the Glide path Or Glideslope.
Gradually, the colours of the lights and their rates of flash became standard worldwide based
on

International

Civil

Aviation

Organization

(ICAO)

standards.

The

Air

Mail

Service'sintermediate or emergency, landing fields that it established along the air route used
rotating electric beacons and lights that were set around the perimeter of the field3.
Developed in the 1940s, the aid consisted of lights in rows that showed the pilot a simple
funnel of two rows that led him to the end of the runway. Other patterns showed him when he

1

NASA Thesaurus, Washington, DC.
Adapted from the United States Air Force Dictionary.
3
ICAO articles 2 july2001PDF format page 12 –history of ILS
2

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was off to the right or left, or too high or low. The system was inexpensive to build and
operate although it had some limitations and was not suitable for certain airports.
Radio navigation aids also assisted in landing. One type, introduced in 1929, was the fourcourse radio range, where the pilot was guided by the strength of Morse code signals. Another
type that was tried experimentally was the low-frequency radio beam4. These radio beams
flared outward from the landing point like a “V,” so at the point farthest from the runway, the
beams were widely separated and it was easy for the pilot to fly between them. But near the
landing point, the space between the beams was extremely narrow, and it was often easy for
the pilot to miss the exact counterpoint that he had to hit for landing. Another new method
had a pilot tune into a certain frequency at a checkpoint far from the airport, and then uses a
stopwatch to descend at a precise rate to the touchdown area of the runway. This method also
proved difficult.
The Instrument Landing System (ILS) incorporated the best features of both approach
lighting and radio beacons with higher frequency transmissions. The ILS painted an electronic
picture of the glideslope onto a pilot's cockpit instruments. Tests of the system began in 1929,
and the Civil Aeronautics Administration (CAA) authorized installation of the system in 1941
at six locations. The first landing of a scheduled U.S. passenger airliner using ILS was on
January 26, 1938, as a Pennsylvania-Central Airlines Boeing 247-D flew from Washington,
D.C., to Pittsburgh and landed in a snowstorm using only the ILS system.
More than one type of ILS system was tried. The system eventually adopted consisted of a
course indicator (called a Localizer) that showed whether the plane was to the left or right of
the runway centreline, a glide path or landing beam to show if the plane was above or below
the glide slope, and two marker beacons for showing the progress of approach to the landing
4


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field. Equipment in the airplane allowed the pilot to receive the information that was sent so
he could keep the craft on a perfect flight path to visual contact with the runway. Approach
lighting and other visibility equipment are part of the ILS and also aid the pilot in landing. In
2001, the ILS remains basically unchanged.
By 1945, nine CAA systems were operating and 10 additional locations were under
construction. Another 50 were being installed for the army. On January 15, 1945, the U.S.
Army introduced an ILS with a higher frequency transmitter to reduce static and create
straighter courses, called the Army Air Forces Instrument Approach System Signal Set 515. In
1949, the International Civil Aviation Organization (ICAO) adopted this army standard for all
member countries. In the 1960s, the first ILS equipment for fully blind landings became
possible.
The development of radar during World War II led to the development of a new precisionbeam landing aid called Ground Control Approach (GCA). GCA worked along with the
ILS to help planes land at busy airports. By 1948, Distance Measuring Equipment(DME)
was being used to provide data relating to the plane's distance from the ground. The
installation of other radar continued with the air-route surveillance type of radar and the
airport-surveillance radars that were installed at a number of airports in the mid-1950s. These
helped air traffic controllers with their job6.
Lights still play an important part in landing. Modern approach lighting can be oriented to
accommodate any obstructions located near the airport that the pilot may need to avoid before
beginning his descent to the runway. Lights can even be set at a second angle for larger
aircraft because those cockpits are farther off the ground and the angle of descent will look

5

Wikipedia articles/www.wikipedia.com/instrumentlandingsystem

6

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different to pilots in these planes. Pilots flying into fields without any staff can often turn
landing lights on or off themselves or change their brightness by tuning their radio to a certain
frequency and clicking their transmitter.
Helicopters have used visual landing procedures for most of their history, and on June 12,
1987, the FAA opened its national concepts development and demonstration heliport. This
research heliport was fully equipped with items such as a microwave landing system as well
as precision approach path indication lights like those used by fixed-wing aircraft7.
2.0 Instrumentation
Instrument or equipment that uses is such as Aircraft’s Cockpit Instrument, Aircraft’s
Antenna and Ground Based Equipment for picture example:

Figure (2)1:Cockpit Instrument and ILS indicator

7

FAA website–http://159.136.429

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Figure (2)2: Aircraft Antenna’s

Figure (2)3: ILS-LocalizerFigure (2)4:ILS-Glide Path

3.0Instrument Landing System
Based on figure (2)3 and figure (2)4 ILS is stand for Instrument Landing System. It
has been existence for over 60 years. But today, it is still the most accurate approach and
landing aid that is used by the airliners. Why need ILS? Scheduled service would be
impossible without a way to land in poor weather. The Tests of using the first ILS began in
1929.The first scheduled passenger airliner to land using ILS was in 19388.The use of ILS is
to guide the pilot during the approach and landing. It is very helpful when visibility is
limitedand the pilot cannot see the airport and runway, to provide an aircraft with a precision
final approach, to help the aircraft to a runway touchdown point, to provide aircraft guidance

8

FAA articles Flight Rules-Authors James Ramno-PDF format-page 5

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to the runway both in the horizontal and vertical planes and to increase safety and situational
awareness.
3.1 Equipment and Component
3.1 Equipment of ILS
ILS consists of Ground Installations and Airborne Equipment.Ground-based
instrument approach system that providesprecision guidance to an aircraft approaching and
landing on a runway, using a combination of radio signals and, in many cases, to enable a safe
landing and also guide the pilot during the approach and landing.It is very helpful when
visibility is limited and the pilot cannot see the airport and runway. ILS component and
Equipment also provide aircraft with a precision final approach.
3.1.1 There are 3 equipment’s for Ground Installations, which are:
i.

Ground Localizer (LLZ) Antenna– To provide horizontal navigation

ii.

Ground Glide path (GP) Antenna– To provide vertical navigation

iii.

Marker Beacons – To enable the pilot cross check the aircraft’s height.

The 3 equipment above are shown on picture figure (2)3 and figure (2)4.
3.1.2 There are 2 equipment’s for Airborne Equipment’s, which are:
i.

Localizer (LLZ) and Glide Path (GP) antennas located on the aircraft nose.

ii.

indicator inside the cockpit

The 2 equipment’s above are shown on picture figure (2)1 and figure (2) as for
picture reference.

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3.2Components of ILS (Principles of Operation)
3.2.1 Localizer (LLZ)

Localizer is the horizontal antenna array located at the opposite end of the runway and
Localizer operates in VHF band between 108 to 111.975 MHz .Localizer transmit two signals
which overlap at the center. The left side has a 90 Hz modulation and the right has a 150 Hz
modulation. The overlap area provides the on-track signal. For example, if an aircraft
approaching the runway center line from the right, it will receive more of the 150 Hz
modulation than 90Hz modulation as shown in figure 3.1.2(1) below. Difference in Depth of
Modulation will energize the vertical needle of ILS indicator for example as figure 3.1.2.1(2).
Thus, aircraft will be given the direction to GO LEFT.

Figure 3.1.2.1(1) show how Localizer works

Figure 3.1.2.1(2)
Figure 3.1.2.1(3)
Needle indicates direction of runwayCentered Needle = Correct Alignment

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3.2.1.1 Localizer Backcourseand Identification

Modern localizer antennas are highly directional. However, usage of older, less directional
antennas allows a runway to have a non-precision approach called a Localizer Backcourse.
This lets aircraft land using the signal transmitted from the back of the localizer array for
example are shown in figure 3.1.2.1.1(1). A pilot may have to fly opposite the needle
indication, due to reverse sensing. This would occur when using a basic VOR indicator.
If using an HSI, one can avoid reverse sensing by setting the front course on the course
selector. Highly directional antennas do not provide a sufficient signal to support a
backcourse. In the United States, backcourse approaches are commonly associated with
Category I systems at smaller airports that do not have an ILS on both ends of the primary
runway. Pilots may notice that they receive false glide slope signals from the front course ILS
equipment. All glide slope information should be disregarded.

Figure 3.1.2.1.1(1) Localizer array and approach lighting at
Whiteman Air Force Base, Knob Noster, Missouri

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3.2.2 Glide Path / Glide Slope

Glide Path or Glide Slope is the vertical antenna located on one side of the runway
about 300 m to the end of runway. Glide Path operates in UHF band between 329.15 and 335
MHz.Glide path produces two signals in the vertical plane. The upper has a 90 Hz modulation
and the bottom has a 150 Hz modulation. For example, if an aircraft approaching the runway
too high, it will receive more of the 90 Hz modulation than 150Hz modulation as shown in
figure 3.1.2.2 below. Difference in Depth of Modulation will energizes the horizontal needle
of ILS indicator.Thus, aircraft will be given the direction to GO DOWN.Glide Path errors can
occur if terrain is sloping or is uneven in front of the antenna. Since antennas point in a single
direction, only “straight” approaches are available.

Figure 3.1.2.2(1) Show How Glide Path Works

Figure 3.1.2.2(2) Needles indicates above/below glide path.

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4.0 Marker Beacon

Figure 4.0(1)
Marker Beacons
Cross check the height aircraft

Marker beacons operating at a carrier frequency of 75 MHz are provided. When the
transmission from a marker beacon is received it activates an indicator on the pilot's
instrument panel and the tone of the beacon is audible to the pilot.
The distance from the runway at which this indication should be received is published in the
documentation for that approach, together with the height at which the aircraft should be if
correctly established on the ILS. Figure 4.0(1) are show marker beacon provides a check on
the correct function of the glideslope. In modern ILS installations, a DME is installed, colocated with the ILS, to augment or replace marker beacons. A DME continuously displays
the aircraft's distance to the runway.

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Figure 4.0(2) Show how ILS component and equipment works and intercepted during aircraft
landing

4.1 Outer Maker
The Outer Marker is normally located 7.2 Kilometres (3.9 NMI; 4.5 MI) from the
threshold except that, where this distance is not practical, the outer marker may be located
between 6.5 To 11.1 Kilometres (3.5 to 6.0 NMI; 4.0 to 6.9 mi) from the threshold9. The
modulation is repeated Morse-style dashes of a 400 Hz tone. The cockpit indicator is a blue
lamp that flashes in unison with the received audio code as shown in figure 4.1(1). The
purpose of this beacon is to provide height, distance and equipment functioning checks to
aircraft on intermediate and final approach. In the United States, a NDB is often combined
with the outer marker beacon in the ILS approach (called a Locator Outer Marker, or LOM);
in Canada, low-powered

Figure 4.1(1) Blue Outer Marker

9

Wikipedia-www.wikipedia.com/markerbeacon

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4.2 Middle Maker
The Middle Marker should be located so as to indicate, in low visibility conditions, the
missed approach point, and the point that visual contact with the runway is imminent, ideally
at a distance of approximately 3,500 ft (1,100 m) from the threshold. It is modulated with a
1.3 kHz tone as alternating Morse-style dots and dashes at the rate of two per second10. The
cockpit indicator is an amber lamp that flashes in unison with the received audio code as
shown in figure 4.2(1). Middle markers are no longer required in the United States, so many
of them are being decommissioned.

Figure 4.2(1)Amber Middle Marker

4.3 Inner Maker
The Middle Marker should be located so as to indicate, in low visibility conditions,
the missed approach point, and the point that visual contact with the runway is imminent,
ideally at a distance of approximately 3,500 ft (1,100 m) from the threshold. It is modulated
with a 1.3 kHz tone as alternating Morse-style dots and dashes at the rate of two per second11.
The cockpit indicator is an amber lamp that flashes in unison with the received audio code as
shown in figure 4.3. Middle markers are no longer required in the United States, so many of
them are being decommissioned.

Figure 4.3(1)White Inner Marker
10


11

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5.0 Monitoring
It is essential that any failure of the ILS to provide safe guidance be detected immediately by
the pilot. To achieve this, monitors continually assess the vital characteristics of the
transmissions. If any significant deviation beyond strict limits is detected, either the ILS is
automatically switched off or the navigation and identification components are removed from
the carrier. Either of these actions will activate an indication ('Failure Flag') on the
instruments of an aircraft using the ILS.
6.0 Approach Lighting
Some installations include medium- or high-intensity approach light systems. Most often,
these are at larger airports but many small general aviation airports in the Langkawi have
approach lights to support their ILS installations and obtain low-visibility minimums.
The approach lighting system (abbreviated ALS) assists the pilot in transitioning from
instrument to visual flight, and to align the aircraft visually with the runway centerline.

Pilot observation of the approach lighting system at the Decision Altitude allows the pilot to
continue descending towards the runway, even if the runway or runway lights cannot be seen,
since the ALS counts as runway end environment. In the U.S, an ILS without approach lights
may have CAT I ILS visibility minimums as low as 3/4 Mile (runway visual range of 4,000
Feet) if the required obstacle clearance surfaces are clear of obstructions.

Visibility minimums of 1/2 Mile (runway visual range of 2,400 Feet) are possible with a CAT
I ILS approach supported by a 1,400-to-3,000-Foot-Long (430 to 910 M) ALS, and 3/8 Mile
visibility 1,800-foot (550 M) visual range is possible if the runway has high-intensity edge
lights, touchdown zone and centerline lights, and an ALS that is at least 2,400 Feet (730 M)
long as shown in table 7.0.

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In effect, ALS extends the runway environment out towards the landing aircraft and allows
low-visibility operations. CAT II and III ILS approaches generally require complex highintensity approach light systems, while medium-intensity systems are usually paired with
CAT I ILS approaches. At many non-towered airports, the intensity of the lighting system can
be adjusted by the pilot, for example the pilot can click their microphone 7 times to turn on
the lights, then 5 times to turn them to medium intensity.

7.0 Instrument Landing System Categories
ILS (instrument landing systems) are categorized according to their capability to
provide for approach to a height above touchdown (HAT)/decision height (DH)
and RVR (runway visual range). Different categories of ILS are as given in the
table12.
ILS category

Height above touch down
(HAT)/decision height (DH)

Runway visual range
Not less than 1800 feet

CAT I

HAT not less than 200 feet

CAT II

HAT not less than 100 feet

CAT III A

No decision height

CAT III B

No decision height
No RVR minimum

CAT III C

No decision height
Table 7.0 Categories of ILS

12

: http://www.answers.com/topic/ils-categories#ixzz22vdTYjRD
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7.1 There are three categories of ILS the operation.
7.1.1 Category I
A minimal height of resolution at 200 feet (60,96 M), whereas the decision
height represents an altitude at which the pilot decides upon the visual contact
with the runway if he’ll either finish the landing maneuver, or he’ll abort and
repeat it.
The visibility of the runway is at the minimum 1800 feet (548,64 M)
The plane has to be equipped apart from the devices for flying in IFR
(Instrument Flight Rules) conditions also with the ILS system and a marker
beacon receiver.

7.1.2 Category II
A minimal decision height at 100 feet (30,48 M)
The plane has to be equipped with a radio altimeter or an inner marker
receiver, an autopilot link, a raindrops remover and also a system for the
automatic draught control of the engine can be required. The crew consists of
two pilots.

7.1.3 Category III -A
A minimal decision height lower than 100 feet (30,48 M)
The aircraft has to be equipped with an autopilot with a passive malfunction
monitor or a HUD (Head-up di)

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7.1.4 Category III - B
A minimal decision height lower than 50 feet (15,24 M)
A device for alteration of a rolling speed to travel speed.

7.1.5 Category III - C
Zero visibility
A precision instrument approach and landing with no decision height and no
runway visual range limitations. A Category III C system is capable of using
an aircraft's autopilot to land the aircraft and can also provide guidance along
the runway surface.

In contrast to other operations, CAT III weather minima do not provide sufficient visual
references to allow a manual landing to be made. The minima only permit the pilot to decide
if the aircraft will land in the touchdown zone (basically CAT III A) and to ensure safety
during rollout (basically CAT III B). Therefore an automatic landing system is mandatory to
perform Category III operations. Its reliability must be sufficient to control the aircraft to
touchdown in CAT III A operations and through rollout to a safe taxi speed in CAT III B (and
CAT III C when authorized)13.

FAA Order 8400.13D allows for special authorization of CAT I ILS approaches to a decision
height of 150 feet (46 M) above touchdown, and a runway visual range as low as 1,400 feet
(430 M). The aircraft and crew must be approved for CAT II operations, and a heads-up

13

http://niquette.com/books/chapsky/skypix/ILS
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display in CAT II or III mode must be used to the decision height. CAT II/III missed
approach criteria applies14.
In Canada, the required RVR for carrying out a Cat I approach is 1600 feet, except for certain
operators meeting the requirements of Operations Specification 019, 303 or 503 in which case
the required RVR may be reduced to 1200 feet.
In the United States, many but not all airports with CAT III approaches have listings for CAT
IIIa, IIIb and IIIc on the instrument approach plate (U.S. Terminal Procedures). CAT III B
runway visual range minimums are limited by the runway/taxiway lighting and support
facilities, and would be consistent with the airport Surface Movement Guidance Control
System (SMGCS) plan15.

Operations below 600 runway visual range require taxiway centerline lights and taxiway red
stop bar lights. If the CAT IIIB runway visual range minimums on a runway end were 600
feet (180 M), which is a common figure in the U.S., ILS approaches to that runway end with
runway visual range below 600 feet (180 M) would qualify as CAT IIIc and require special
taxi procedures, lighting and approval conditions to permit the landings. FAA Order
8400.13D limits CAT III to 300 runway visual range or better. Order 8400.13D, which was
released during 2009, also allows special authorization CAT II approaches to runways without
ALSF-2 approach lights and/or touchdown zone/centerline lights, which has expanded the
number of potential CAT II runways16.

In each case, a suitably equipped aircraft and appropriately qualified crew are required. For
example, CAT IIIb requires a fail-operational system, along with a crew who are qualified
14

16
15

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and current, while CAT I does not. A head-up display which allows the pilot to perform
aircraft maneuvers rather than an automatic system is considered as fail-operational. CAT I
relies only on altimeter indications for decision height, whereas CAT II and CAT III
approaches use radar altimeter to determine decision height.
An ILS is required to shut down upon internal detection of a fault condition. With the
increasing categories, ILS equipment is required to shut down faster, since higher categories
require shorter response times. For example, a CAT I localizer must shutdown within 10
Seconds of detecting a fault, but a CAT III localizer must shut down in less than 2 Seconds17.

8.0 ILS Critical Sensitive Areas

When CAT II/III operations are in progress, unauthorized vehicles and/or aircraft will
not be permitted within the critical or sensitive areas. Examples of critical or sensitive areas
are outlined in Figure C-3A and C-3B. Current regulatory requirements mandated in subpart 2
of Part VIII of the CARs are contained in ICAO Annex 10, vol. 1 Critical areas are defined as
those where the presence of a vehicle or taxiing aircraft may possibly affect ILS signals.
The depicted areas are theoretical, and will probably vary with individual sites. Actual critical
areas can be defined only by experimentation and experience. When any portion of a
designated sensitive area becomes suspect as a likely source of interference, that portion must
be included as part of the critical area. “CAT II/III Hold” signs are posted on taxiways and
must be observed by aircraft and vehicles when CAT II/III operations are being conducted.

17

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a) When snow clearance is necessary, snow removal equipment may enter
and remain in these areas. It is expected that vehicles must vacate these
areas before an aircraft using the ILS for a CAT II/III approach has passed
the Final Approach Fix (FAF) (usually a point 4 NM from threshold);
such vehicles may not reenter until the aircraft has landed or commenced
a missed approach.
b) A telecommunications vehicle may be authorized to proceed to the ILS
equipment buildings provided that an aircraft on a CAT II/III approach
has not passed the FAF. If already at the building however, such a vehicle
must remain parked there until authorized to move by ATC.
c) No vehicle or aircraft will be permitted to cross or remain on an active
CAT II/III runway, or on any other runway or taxiway where their
presence could affect ILS signals, when an aircraft on a approach has
passed the FAF.
d) If there is a roadway in the glide path sensitive areas, no vehicle will be
permitted to stop or park on that roadway. Signs must be posted to
indicate these restrictions.

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8.1 Snow Removal – Category II/III Glide Path Sites
Accumulation of snow beyond certain depths in the monitor area may result in the monitor
indicating alarm conditions, whereas the actual path parameters along the approach may not
change significantly. A heavy accumulation of snow outside the monitor area may result in an
increase in glide slope angle of approximately 0.1º per foot of snow. Under these conditions,
snow clearing in the monitor area only would result in normal monitor indications, when in
fact, the glide slope angle may have increased along the approach path. At the same time, a
change in the coefficient of reflection and the relative heights of the transmitting antenna may
also affect course structure.

NAV CANADA delivers mandatory annual briefings to airport personnel responsible for
snow measurement and removal at all of its ILS sites, regardless of precision approach
category. Responsibilities for removal of snow and vegetation are as outlined in site specific
agreements

between

the

ILS

owner/operator

and

the

airport authority.

The critical area is shown in Figure 8.0(1) and 8.0(2). This area is considered to be critical in
terms of ground conditions, vehicles intrusion, etc. The removal of snow and vegetation is the
responsibility of the Local Airport Authority (LAA). Excessive snow banks and vegetation
along the approach and access roads at some locations may affect course structure, the degree
being dependent on location of the approach road. Following a period of heavy snowfall and
subsequent plowing, it may be necessary to have the banks cut down. This is particularly
important in areas where snowblowing operations have created vertical snow cuts. Similarly,
snow drifts or banks in the monitor area may affect monitor operation and must be tapered.

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8.1 Example of ILS Critical Sensitive Areas

Figure 8.0 (From ICAO Annex 10) Typical localizer critical and sensitive areas
dimension variations for a 3 000 m (10 000 ft) runway

Table below Based on Figure 8.0
Example 1

Localizer antenna
aperture

Example 3

B-747

Aircraft type

Example 2
B-747

B-727

Typically 27 m
(90 ft)
(Directional dual
frequency,
14 elements)

Typically 16 m
(50 ft)
(Semi-directional,
8 elements)

Typically 16 m (50 ft)
(Semi-directional,
8 elements)

Sensitive area (X, Y)
Category I

600 m (2 000 ft)

300 m (1 000 ft)

60 m (200 ft)

110 m (350 ft)

60 m (200 ft)

X

1 220 m (4 000 ft)

2 750 m (9 000 ft)

300 m (1 000 ft)

Y
Category III

600 m (2 000 ft)

Y
Category II

X

90 m (300 ft)

210 m (700 ft)

60 m (200 ft)

X

2 750 m (9 000 ft)

2 750 m (9 000 ft)

300 m (1 000 ft)

Y

90 m (300 ft)

210 m (700 ft)

60 m (200 ft)

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Figure 8.0(2)(From ICAO Annex 10). Typical glide path critical and
sensitive areas dimension variations

Example 1

Example 3

B-747

Aircraft Type

Example 2
B-727

Small & Medium*

915 m (3 000 ft)

730 m (2 400 ft)

250 m (800 ft)

60 m (200 ft)

30 m (100 ft)

30 m (100 ft)

X

975 m (3 200 ft)

825 m (2 700 ft)

250 m (800 ft)

Y

Category
II/III

X

Y

Category I

90 m (300 ft)

60 m (200 ft)

30 m (100 ft)

* Small and medium aircraft here are considered as those having both a length
less than 18 m (60 feet) and a height less than 6 m (20 feet)
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9.0 How does the Instrument Landing System work?

The Instrument Landing System uses radio transmitters on the ground and receivers in
the air to provide an aircraft with precise guidance for landing even in very low or zero
visibility conditions.
The ILS has two main parts: a localizer, which guides the airplane horizontally, and a glide
slope, which guides the airplane vertically. The localizer uses a set of radio transmitters at the
far end of a runway, and the glide slope uses a set of transmitters close to the near threshold of
the runway.
Receivers on the aircraft detect the localizer and glide slope transmissions. These highly
directional radio transmissions are designed so that the aircraft receives a signal of perfect
alignment only if it is right on the extended centerline of the runway and descending exactly
along the required descent path for touchdown. The receivers on the aircraft are used to drive
instruments that display the aircraft's position to the pilots, and they can be used to control
autopilots that can fly the landing approach automatically.
In most airliners, the ILS receivers can even land the plane entirely under automatic control,
without any pilot intervention (this is called an "autoland"). This requires a special category of
ILS, plus special ILS receivers on the airplane, and special training for the pilots. For more
ordinary ILS approaches, the pilots normally take over from the autopilot (if it is in use) just
before reaching the runway. Of course, pilots can fly the ILS approach by hand, too, by
watching their instruments.
ILS is routinely used any time the weather is poor, and often it is used all the time, as back-up
to a visual approach. In the worst visbility conditions, autoland allows aircraft to land even if
they pilots can't see anything at all outside the windows.

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9.1 ILS Picture (Individuals Parts of ILS)

Figure 9.1(1) the description and placement of the individual parts of the ILS
system

The Figure above show how ILS does work with the ILS Glide Slope and Localizer and also
the component of Maker Beacon:i.

Outer

ii.

Middle

iii.

Inner

All the individual parts must work well to provide aircraft landing with the accurate path of
runway. This system will guide the aircraft to the center of runway.

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10.0 Rate-Of-Descent Formula
A useful formula pilots use to calculate descent rates (standard 3° Glide Slope):
Rate Of Descent = Ground Speed ⁄ 2 × 10
Or
Rate Of Descent = Ground Speed × 5
For other glideslope angles:
Rate Of Descent = Glide Slope Angle × Ground Speed × 100 / 60
The latter replaces tan α (see below) with Α/60, which is about 95% accurate up to 10°.
Example:
120 KTS × 5
Or
120 KTS / 2 × 10
= 600 FPM
The above simplified formulas are based on a trigonometric calculation:
Rate Of Descent = Ground Speed × 101.25 × Tan Α
where:


Α is the descent or Glideslope Angle from the horizontal (3° being the standard)



101.25 (FPM⁄KT) is the conversion factor from knots to feet per minute (1 KNOT ≡
1 NM⁄H =6075 FT⁄H = 101.25 FPM)
Example:
Ground Speed = 250 KTS
Α = 4.5
KTS
250
× 101.25FPM/KT × TAN 4.5
= 1992 FPM

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11.0 The Benefits of an ILS (Instrument Landing System)

The Instrument Landing System (ILS) is a precision approach navigational aid
which provides highly accurate course, glide-slope, and distance guidance to a
given runway. The ILS can be the best approach alternative in poor weather
conditions for several reasons.

1. The ILS is a more accurate approach aid than any other widely available
system.

2. The increased accuracy generally allows for lower approach minimums.
3. The lower minimums can make it possible to execute an ILS approach and land
at an airport when it otherwise would not have been possible using a NonPrecision Approach

Figure 11.0 Show When flying an ILS, you track the line formed by the intersection
of the glide slope and localizer courses.

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11.1Disadvantages of ILS
Interference due to large reflecting objects, other vehicles or moving objects. This
interference can reduce the strength of the directional signals.

12.0 Future Development of Instrument Landing System

Microwave Landing Systems(MLS) were developed in the 1980s. These systems allow
pilots to pick a path best suited to their type of aircraft and to descend and land from more
directions than the ILS. Having different landing patterns can help reduce noise around
airports and keep small aircraft away from the dangerous vortices behind large aircraft. MLS
have been adopted in Europe as replacements for ILS. In the United States, however, the FAA
halted further development of MLS in 1994. Instead, the FAA is considering the use of
technology based on the Global Positioning System(GPS) instead of, or in addition to,
existing microwave systems. The GPS uses satellites for navigation between airports and is
exceedingly precise18.

18

Aeronautical navigation product

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13.0 Conclusion
An instrument landing system (ILS) isa ground-based instrument approach system that
provides precision guidance to an aircraft approaching and landing on a runway, using a
combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe
landing during instrument meteorological conditions (IMC), such as low ceilings or reduced
visibility due to fog, rain, or blowing snow.
Additional aids may be available to assist the pilot in reaching the final approach fix.
One of these aids is the NDB which can be co-located with or replace the outer marker (OM)
or back marker (BM). It is a low-frequency non-directional beacon with a transmitting power
of less than 25 watts (W) and a frequency range of 200 kilohertz (kHz) to 415 kHz. The
reception range of the radio beacon is at least 15 nautical miles (NM). In a number of cases an
en route NDB is purposely located at the outer marker so that it may serve as a terminal as
well as an en route facility.
So this equipment is very important to the aviation industry it is also the main factor of
air transport is safe transport in the world than compare with ground and others.

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14.0 Bibliography
wikipedia. (2006, 06 04). Retrieved from http://wikipedia.com/makerbeacon
Dictionary, A. (1999). US airforce dictionary. Retrieved from http://USairforce
Elbert, R. (2005). FAA flight Rule. uniques.
ICAO. (2001, july 2). PDF. Retrieved from http://ICAO/airport annexes
NASA. (n.d.). NASA Theasaurus. Retrieved from Washington DC.
Nirqutee. (2001). nirqurtee. Retrieved from http://niqurtee.com/books/chapsky/skypix/ils
Rovertivesy. (n.d.). answer. Retrieved from http://www.answer.com/topic/ils-category

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