ILS Flashcards
What is ILS used for
Precision approach landing system
Why is ILS considered ‘precision’
As it provides course guidance (localiser) and vertical guidance (glideslope)
What are the characteristics of a Cat 1 ILS
- has decision height (not lower than 200ft)
And either: - vis > 800m
- RVR > 550m
What are the 3 main components of an ILS
- VHF localiser
- UHF glideslope
- Marker beacons, DME, or low powered NDBs
Where is an localiser antenna usuall located
Beyond the departure end of the runway, along centreline
What are the characteristics of a localiser transmitter/ how does it work
- VHF frequencies from 108 to 112 MHz (equal signals)
- two overlapping signal lobes:
- 90 Hz (right)
- 150 Hz (left)
Does the glideslope operate on the same principle of the localiser
Yes
Which direction is the 90Hz transmitted to, up or down of the glideslope
Up
Whats the most common glideslope angle
3°
How is range information displayed for an ILS approach
- ILS paired DME
- DME
- marker beacon(s)
- compass locator
What type of chart would you see Marker Beacons on
Instrument Approach Procedure chart
What two types of marker beacon are generally used
Outer, middle
What is a compass locator primarily used for
Navigating for a dist of approx 15miles to tower, usually at site of OM or MM
What is the use of approach lights
Provide visual reference and cues to assist ILS approach
What are the 2 types of precision approach lighting systems
- Dist coded centreline
2. Barrette centreline
Describe dist coded centreline lights
Lights spaced 150m apart, spaning out further away from the runway
How many degrees does 1 dot on the lateral deviation scale equate to?
1.25
And on the glideslope
0.35°
What are the rated coverage parameters for a localiser signal
25nm, 2000ft agl and 10° either side of centreline
What are other requirements of a localiser signal
That there are reliable indications 35° of centreline for 17NM
What is the ICAO Annex 10 definition of what glideslope coverage requires
Signal be accurate over vertical angle between 45% and 175% of ideal approach angle out to 10NM within 8° of centreline of localiser
At what range is a glideslope considered accurate/ reliable
10NM
At what degree above horizontal would you generally see a false glideslope, and what are some symptoms
12.5°. Noticed by oscillating needle
What is a way to double check if youre on an ISL
Verify altitude using TACAN
An ILS is susceptible to interference from what 2 sources
- Vehicles and aircraft near antennas
2. Buildings near antennas
When would an “off flag” or ‘flag alarm’ been seen on an instrument
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
Are LOC and GS generally described as “fly to” indicators?
Yes
