instrument landing system (ils) · instrument landing system (ils) once established on an approach,...

AIR NAVIGATION PROF. A.M.ALLAM

Instrument Landing System (ILS)

Once established on an approach, pilot will follow the ILS and descend along

the glideslope, until the Decision Height (DH) is reached

At this point, the pilot must have the runway or its approach lights in sight to

continue the approach

Otherwise, the approach must be aborted and a missed approach procedure will be

performed i.e., the A/C will climb back to a predetermined altitude and position


Provides an A/C with: a precision final approach to the runway with horizontal and

vertical guidance to the runway to enable a safe landing

It uses a combination of: radio signals and, in many cases, high intensity lighting arrays

to enable a safe landing

Used by pilots landing at an airport when there is poor weather and/or low visibility

The ground equipment contains:

-Localizer transmitter (provides horizontal or lateral navigation)

-Glide path transmitter (provides vertical navigation)

-Marker beacons and/or distance measuring equipment DME (Provides distance

from runway)

-Approach lighting system (transition from instrument monitoring to visual marking

lights)

Onboard A/C equipment:

- RXs

-Localizer and glide slope antennas in the A/C nose

-ILS indicator inside the cockpit

Introduction


International Civil Aviation Organization (ICAO)

makes ILS category according to

ILS Categories

Category Decision Height (above threshold)

Runway Visual Range RVR limit Visibility

I 200 ft 550 m or 2400 ft (1800 ft is approved at some airports) 800 m

II 100 ft 350 m or 1200 ft N/A

IIIa 50 ft < DH < 100 ft 200 m (700ft) N/A

IIIb 0 < DH < 50 ft 200m > RVR limit > 75 m (150 ft) N/A

IIIc No DH No RVR N/A

Category IIIc is not yet in operation anywhere

Category IIIb is currently the best available system


ILS constellation

Approach light system

ILS indicator inside the cockpit


http://www.youtube.com/watch?v=KVtEfDcNMO8

Glide

slope

Localizer


Localizer

A localizer is a highly directive VHF ground radio transmitter in the range (108.1 – 111.95 MHz)

using the same general range as VOR transmitters to provides lateral guidance. The frequencies

of the localizer are only placed on odd decimals; where the tenths of a megacycle is odd so, for

example 108.10 and 108.15 MHz are localizer and are not used for any other purpose while 108.20

and 108.25 MHz are not, but can be allocated to VOR

It is usually located on the centerline at the opposite end of the runway

The transmitted signal is produced using a circularly polarized antenna array

The right lobe carrier is AM by 90 Hz and the other by 150 Hz tones

The localizer is identified by an audio signal superimposed on the navigational signal

To avoid interference from another localizers, every localizer has a two letter identification

preceded by the letter "I“


The array is composed of 14 separate but colocated elements. Each lobe is

produced by 7 array elements, one slightly to the left of the runway

centerline and the other to the right

The beamwidth is varied

from approximately 3º to

6º, with 5º being normal


The directivity of the localizer antenna depends on wither ,it is Back or Forward course

-A backcourse localizer is also used on some ILS systems

-A Localizer Back Course is just like a regular localizer approach except that left is right, and

right is left. In addition, it may, or may not, have a Glide Slope. If it has a Glide Slope, it is called

a "Localizer Back Course with Glide Slope"

-The backcourse is intended for landing purposes and it’s secured with a 75 MHz marker beacon


The received signal in the A/C receiver activates a vertical needle

called the Track Bar (TB) in Course Deviation Indicator (CDI)

The receiver is combined with the VOR receiver unit

The TB is deflected to the left if the A/C is east (right) of the

extended centerline of the runway (in the area modulated at 150Hz)

The TB is deflected to the right if the A/C is west (left)

of the extended centerline of the runway (in the area

modulated at 90Hz)

The A/C is

1° left of

course (shift

right to

return)

The A/C is

1° right of

course (shift

left to

return)

Represents the

difference between the

localizer position and

the A/C position

At the point where the 90 Hz and 150 Hz signals are of equal

intensity, the TB is centered, indicating that the A/C is

located precisely on the approach track (in the course)

Course Deviation Indicator


If an A/C is to the left side of the

centerline , the 90 Hz

modulation exceeds that of the

150 Hz

CDI vertical needle is deflected

towards the right side

The action is the A/C should shift right to be in the course

Operation


On the contrary, if an A/C is to

the right side of the centerline,

the 150 Hz modulation will

exceed that of 90 Hz

CDI vertical needle is deflected

towards the left side

The action is the A/C should turn left to be in the course


If the A/C on approach with the runway

centerline

CDI will display Difference in Depth of

Modulation; DDM=0 between 90 and 150

Hz and the CDI needle is centered

Implying that the plane is located exactly

in the approach axis as shown in the

figure

Localizer information is typically displayed on a CDI which is used by the pilot

until visual contact is made and the landing completed


• VHF Signal Processor: Maintains a favourable SNR ratio suitable for detection

• Signal Amplifiers: Electronic device that can increase the power of a signal

Transmitter


The onboard equipment localizer is an antenna system composed of a VHF receiver, and

is located inside the A/C

The localizer receiver and the VOR receiver form a single unit

This equipment enables to receive the localizer signal by an onboard VHF localizer

receiver, process it and to display the A/C’s position on an onboard indicator

• The indicator full scaled deflection is achieved when the DDM is 0.155

• The pilot should keep the DDM zero, where, the A/C will approach the

runway threshold along the course line

Receiver


Localizer reflected signals affect

the ILS performance and hence the

degrade quality due to scattered

beams

Localizer is sensitive to

obstructions like buildings and

terrains

Since antennas point in a single

direction, only “straight”

approaches are available

Can be costly

Microwave Landing System

-Curved approaches are possible

-Less interference and more

accurate than traditional ILS

Transponder Landing System

-Easy to deploy in remote areas

-No additional equipment needed

on A/C

Localizer limitations Localizer Enhancement


3/29/2020 LECTURES 16

5-Glideslope

Operates at a range of 329.3-335 MHz, with a 50 KHz spacing between each channel

Provides vertical guidance (guides the pilot’s rate of

descent) of the A/C during the ILS approach

The signals are arranged unlike the localizer, on top of each

other such that the upper signal has a 90 Hz modulation and

the bottom signal has a 150 Hz modulation

A system of vertical guidance to touchdown zone in elevation

plane is provided by two overlapping lobes producing on inclined

plane of equal signal


3/29/2020 LECTURES 17

Composed of a ground based UHF radio transmitter and antenna system,

UHF receiver in A/C receives the glide slope signal

Glide Slope (GS) or Glide Path (GP) antenna array is

located at one side of the runway touchdown zone

Is located 225–380 meters from the approach end and 120–210

meters to the side of the runway centerline


3/29/2020 LECTURES 18

The glide path angle is normally adjusted to

3 degrees above horizontal

The thickness of the overlap area is 1.4º or 0.7º above and

0.7º below the optimum glide slope


3/29/2020 LECTURES 19

Glide path angle is the angle between the glide path & the horizontal plane

(θo =3 degrees)


3/29/2020 LECTURES 20

• The pilot controls the A/C so that the glide slope CDI needle remains centered on the

display to ensure the A/C is following the glide path to remain above obstructions and

reach the runway at the proper touchdown point

• Localizer (LOC) and glide slope (G/S) carrier frequencies are paired so that the

navigation radio automatically tunes the GS frequency which corresponds to the

selected LOC frequency

• The LOC signal is in the 110 MHz range (VHF) while the G/S signal is in the

330 MHz (UHF) range

• The correct frequency of the glide slope beacon is tuned automatically at the instant

when the localizer’s frequency is selected


3/29/2020 LECTURES 21

It informs the pilot how much above or below the path, the A/C is

The pilot’s objective is to fly the A/C so that the CDI needle is

always centered

The transmitted signal contains 90 Hz & 150 Hz sidebands that are amplitude

modulated and broadcast with the RF carrier

ttmtmEtE cCSBCSB sin]sinsin1[)( 1501509090

The glide slope receiver detects the modulations

Measures the signal strength of the tones (90,150)

Compares them against the strength of the carrier

These two quantities are the Difference in Depth of Modulation (DDM)

The DDM is then displayed for the pilot on Course Deviation Indicator (CDI)

90150 mmDDM

Operation


3/29/2020 LECTURES 22

Indicates 150 Hz dominance ( fly UP)

Indicates 90 Hz dominance ( fly DOWN)

+ve DDM

-ve DDM

DDM=0 A/C is on the correct glide path

Indicates that 90 Hz is dominant

(fly down)

Indicates that 150 Hz is dominant

(fly up)


3/29/2020 LECTURES 23

2600 ft

4-7 miles

Runway

3500 ft

200 ft

O M M M

-Modulated audio signal at

400 Hz on a 75MHz carrier

frequency

-Blue light flashes

-Modulated audio

signal at 1300 Hz

on a 75MHz carrier

frequency

-Yellowlight flashes

I MPlaced 1000 ft before the runway

Modulated audio signal at 3000 Hz.

A White light flashes

A/C is less than 200 ft above ground

6-Maker beacons

Provide information on distance from

runway

instrument landing system (ils) · instrument landing system (ils) once established on an approach,...

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