ILS Flashcards by Unknown Unknown

ILS provides what

Vertical guidance down glide path + Horizontal guidance along centreline (localiser)

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Localiser

Provides guidance left and right to runway
VHF transmitter with 40 dedicated frequencies between 108/111.95MHz

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Glide Path

Up and down guidance on approach
Transmits in the UHF/paired with VHF localiser frequency

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ILS Frequency Band

VHF - 108MHz to 112MHz
Odd numbers less than 112 in the VHF band

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Components of ILS

Localiser
Glide slope
DME range to indicate distance
Market beacons

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ILS is identified by

3 letter Morse code

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Principles of localiser

Difference of depth of modulation
Blue lobe - 150Hz
Yellow lobe - 90Hz

Modulation increases across lobe to max furthest from centreline
Ac receiver detects and measures depth of modulation in each lobe and calculates the difference.

More 90Hz than 150Hz = left of centreline
More 150Hz than 90Hz = right of the centreline

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Errors associated with false localiser beams

Reversed sense side lobes cause incorrect indication of the detected modulated frequency (fly right command when already right of centre line)

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Localiser coverage range

Protected ranges +- 10 degrees of runway centreline out to 25nm
+- 35 degrees out to 17nm

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Localiser back course

Non precision approach on the opposite side on runway - azimuth guidance

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Glide path - principles of operation

Vertical guidance by overlapping beams of UHF carrier waves

Lower (blue) - 150Hz
Upper (yellow) - 90Hz

More 150Hz signal than 90Hz = below the GP (fly up command)
More 90Hz signal than 150Hz = above the GP (flow down command)
Equal amount of each signal = DDM zero on glide path

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Glide path Coverage

+- 8 degrees either side of runway centreline - 10nm

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False glide path

Lower lobe is blocked by the ground/occurs above true glide path 2x
Standard 3 degree glide path = first false glide path occurs at 3 x 2 = 6 degrees

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Outer Marker

Indicated the final approach fix
4-7nm from runway threshold
Lowest frequency of the three (400hz)
Blue flashing lights

2 dashes per second - - - - - - - -

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Beam Bends

Slight curves which are caused by reflections of the radio wave due to obstructions. Can be followed by the navigation system of aircraft

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Middle Marker

1nm from threshold
Amber
Medium frequency (1300Hz)
Dots and dashes - 3 dashes per second - . - . - . - . - . -

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FM broadcast just below 108MHz can cause

Interference with localiser signal which may lead to deviation

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ILS beam bends are

Slight curves caused by reflection of radio waves due to permanent obstructions. Can be followed by nav systems.

Checked by flight tests

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ILS warning flag indicates one of the following

Absence of carrier frequency
Absence of modulation
% of modulation reduced to zero

Different type of precision approaches in ILS

CAT I - Not below 200ft (DH) - RVR 550m
CAT II - DH 100ft - RVR 300M
CAT IIIA - DH below 100ft - RVR 200m
CATIIIB - DH below 100ft or no DH - 75m
CATIIIC - No limits - guides along runway

Scalloping and ILS

Causes rapid indicator changes from side to side of the intended approach path which cannot be followed by the aircraft

To be fully established on the localiser before descending on the glide slop the ac must be within

1 dot half scale deflection on either side of the localiser centreline.

Paired VOR and ILS on approach with half scale deflection of VOR =

Full scale ILS (2.5 max deviation)

FM immunity filters

Used to protect against interference from VHF broadcast transmissions on the localiser and VORs

Not ILS glide slope as this is UHF

Warning flag on ILS will trigger when

No carrier frequency No modulation % modulation reduced to zero

Localiser coverage

25Nm within 10 degrees of approach bearing 17N, within 35 degrees of approach bearing

ILS back course on OBI and CDI

OBI will always display reverse sensing HSI can be turned to face the front course to reverse the indication to give correct sensing of localiser

Full scale deflection of a localiser is

2.5 degrees (Each dot is 0.5 degrees)

Identification of ILS is by

3 letter Morse code Transmitted every 10 seconds on audible channel of the ILS Via the audio control panel in NAV

ILS/DME - co located meaning

DME will read 0nm at the threshold Automatically tuned when localiser frequency is used

How does ILS produce guidance

A radiation pattern which is amplitude modulated by a 90Hz and 150Hz signal

Full deflection on a glide slope indicator indicates the aircraft is

0.7 degrees above or below the correct glide path

ILS lobes - frequencies

The same carrier frequency - VHF - 75MHz Both Amplitude modulated Different amplitude modulation

Outer Marker is modulated at

400hz - - - - - - - Rate of 2 per second 4-7nm for threshold

Middle Marker is modulated at

1300hz .-.-.-. 2 dashes and 6 dots per second 0.4nm

Inner Marker is modulated at

3000 hertz (highest frequency) 6 dots per second . . . . . . . .

Audio frequency of markers

Inner - 3000hz Middle - 1300hz Outer - 400hz

ILS facility performance categories (ILS equipment capability\0

Not the same as the normal operation figures. Lowest minimums capability of the facility. CAT I - 100ft or less CAT II - 50ft or less CAT III - Down to the runway

Glide path Coverage formula

(Glide slope in degrees) x 0.45 (lower) (Glide slope in degrees) x 1.75 (upper) 3 x 0.45 = 1.35 degrees above the horizontal 3 x 1.75 = 5.25 degrees above the horizontal

Tuned to a ILS - rotating the OBS will

Only rotate the compass card and not have any effect on the deviation display

Warning flag appears for ILS when

Absence of the modulation Percentage modulation signal reduced to 0 Absence of the carrier frequency

Working out height along glideslope

3 degree glide slope = 300ft per mile 4 degree glide slope = 400ft per mile +100ft per1 degree

ILS components - Distances of localiser/glide path/middle market/outer marker

Localiser - 300 meters behind end of runway Glide path - 300 meter behind threshold Middle marker - 1000 meter from threshold Outer marker - 4nm from threshold

Type A vs Type B

Type A - Above 250 DH Type B - Below 250 DH

What is the reversal procedure

Starts at fix Straight leg with track guidance/timed 80 degree turn 260 turn in opposite direction to intercept inbound track

Multi path Errors are to be expected in the

ILS coverage area Reflect the ILS signals