ILS paperwork air traffic control

Instrument Landing System (ILS) Case Study

Table of contentsContents

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……………………………………………………. 73.2.1.1: Localizer Back course…………………………… 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

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7.0: ILS Categories………………………………………………………………. 15

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

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1.0 Introduction and Its History

Instrument Landing System is landing navigational Aids that are used widely in

airlines and it also using radio waves to transmit signal. Radio is the 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 the air 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's

intermediate 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.

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

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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

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

four-course 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

4 ICAO articles 2 july2001PDF format page 14 –history of ILS

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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 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 51 5. 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

precision-beam 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

5 ICAO articles 2 july2001PDF format page 14 –history of ILS6 Wikipedia articles/www.wikipedia.com/instrumentlandingsystem

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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 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-Localizer Figure (2)4: ILS-Glide Path

3.0 Instrument 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

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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 limited

and 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 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 provides precision 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.

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

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ii. indicator inside the cockpit

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

picture reference.

3.2 Components 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

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

3.2.1.1 Localizer Backcourse and 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.

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Figure 3.1.2.1.1(1) Localizer array and approach lighting at

Whiteman Air Force Base, Knob Noster, Missouri

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

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

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

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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, co-

located with the ILS, to augment or replace marker beacons. A DME continuously displays

the aircraft's distance to the runway.

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

9 Wikipedia-www.wikipedia.com/markerbeacon

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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

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

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


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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

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.


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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.

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

high-intensity 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

12 : http://www.answers.com/topic/ils-categories#ixzz22vdTYjRD

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CAT I HAT not less than 200 feet

Not less than 1800 feet

CAT II HAT not less than 100 feet


CAT III A No decision height


CAT III B No decision height


CAT III C No decision height

No RVR minimum

Table 7.0 Categories of ILS

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)

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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)

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.

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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 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

13 http://niquette.com/books/chapsky/skypix/ILS14 http://niquette.com/books/chapsky/skypix/ILS15 http://niquette.com/books/chapsky/skypix/ILS

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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

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

16 http://niquette.com/books/chapsky/skypix/ILS17 http://niquette.com/books/chapsky/skypix/ILS

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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.

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.

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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.

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

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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 snow blowing operations have created vertical snow

cuts. Similarly, snow drifts or banks in the monitor area may affect monitor operation and

must be tapered.

8.1 Example of ILS Critical Sensitive Areas

Table below Based on Figure 8.0

Example 1 Example 2 Example 3

Aircraft type B-747 B-747 B-727

Localizer antennaaperture

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)

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Category I X 600 m (2 000 ft) 600 m (2 000 ft) 300 m (1 000 ft)

Y 60 m (200 ft) 110 m (350 ft) 60 m (200 ft)

Category II X 1 220 m (4 000 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)

Category III 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)

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

Example 1 Example 2 Example 3

Aircraft Type B-747 B-727 Small & Medium*

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Category I X 915 m (3 000 ft) 730 m (2 400 ft) 250 m (800 ft)

Y 60 m (200 ft) 30 m (100 ft) 30 m (100 ft)

Category II/III

X 975 m (3 200 ft) 825 m (2 700 ft) 250 m (800 ft)

Y 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)

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.

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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.

9.1 ILS Picture (Individuals Parts of ILS)

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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.

10.0 Rate-Of-Descent Formula

A useful formula pilots use to calculate descent rates (standard 3° Glide Slope):

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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 = 4.5 250 KTS × 101.25FPM/KT × TAN 4.5= 1992 FPM

11.0 The Benefits of an ILS (Instrument Landing System)

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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 Non-

Precision Approach

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

11.1 Disadvantages 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

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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.

13.0 Conclusion

An instrument landing system (ILS) is a 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

18 Aeronautical navigation product

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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.

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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Education

ILS paperwork air traffic control