ILS

Question 1

What is ILS used for

Answer 1

Precision approach landing system

Question 2

Why is ILS considered ‘precision’

Answer 2

As it provides course guidance (localiser) and vertical guidance (glideslope)

Question 3

What are the characteristics of a Cat 1 ILS

Answer 3

• has decision height (not lower than 200ft)
  And either:
• vis > 800m
• RVR > 550m

Question 4

What are the 3 main components of an ILS

Answer 4

1. VHF localiser
2. UHF glideslope
3. Marker beacons, DME, or low powered NDBs

Question 5

Where is an localiser antenna usuall located

Answer 5

Beyond the departure end of the runway, along centreline

Question 6

What are the characteristics of a localiser transmitter/ how does it work

Answer 6

• VHF frequencies from 108 to 112 MHz (equal signals)
• two overlapping signal lobes:
  
  • 90 Hz (right)
  • 150 Hz (left)

Question 7

Does the glideslope operate on the same principle of the localiser

Answer 7

Yes

Question 8

Which direction is the 90Hz transmitted to, up or down of the glideslope

Answer 8

Up

Question 9

Whats the most common glideslope angle

Answer 9

3°

Question 10

How is range information displayed for an ILS approach

Answer 10

• ILS paired DME
• DME
• marker beacon(s)
• compass locator

Question 11

What type of chart would you see Marker Beacons on

Answer 11

Instrument Approach Procedure chart

Question 12

What two types of marker beacon are generally used

Answer 12

Outer, middle

Question 13

What is a compass locator primarily used for

Answer 13

Navigating for a dist of approx 15miles to tower, usually at site of OM or MM

Question 14

What is the use of approach lights

Answer 14

Provide visual reference and cues to assist ILS approach

Question 15

What are the 2 types of precision approach lighting systems

Answer 15

1. Dist coded centreline

2. Barrette centreline

Question 16

Describe dist coded centreline lights

Answer 16

Lights spaced 150m apart, spaning out further away from the runway

Question 17

How many degrees does 1 dot on the lateral deviation scale equate to?

Answer 17

1.25

Question 18

And on the glideslope

Answer 18

0.35°

Question 19

What are the rated coverage parameters for a localiser signal

Answer 19

25nm, 2000ft agl and 10° either side of centreline

Question 20

What are other requirements of a localiser signal

Answer 20

That there are reliable indications 35° of centreline for 17NM

Question 21

What is the ICAO Annex 10 definition of what glideslope coverage requires

Answer 21

Signal be accurate over vertical angle between 45% and 175% of ideal approach angle out to 10NM within 8° of centreline of localiser

Question 22

At what range is a glideslope considered accurate/ reliable

Answer 22

10NM

Question 23

At what degree above horizontal would you generally see a false glideslope, and what are some symptoms

Answer 23

12.5°. Noticed by oscillating needle

Question 24

What is a way to double check if youre on an ISL

Answer 24

Verify altitude using TACAN

Question 25

An ILS is susceptible to interference from what 2 sources

Answer 25

1. Vehicles and aircraft near antennas

2. Buildings near antennas

Question 26

When would an “off flag” or ‘flag alarm’ been seen on an instrument

Answer 26

When a usabke signal isnt being recieved from ground equipment
Or
Either reciever is malfunctioning to such an extent that the output isnt sufficient to hold the flag alarm out of sight

Question 27

Are LOC and GS generally described as “fly to” indicators?

Answer 27

Yes