The ILS (16-05-18)

Question 1

What is the emission class of the ILS?

Answer 1

A8W

Question 2

What is the frequency of the ILS localiser?

Answer 2

108.1 - 111.95MHz

Question 3

What frequency band does the ILS localiser operate on?

Answer 3

VHF

Question 4

What frequency band does the glide path of the ILS operate on?

Answer 4

UHF (approx 333MHz)

Question 5

What are the 4 main components of an ILS system?

Answer 5

LOC

Glidepath

Markers (older systems)

DME (newer systems)

Question 6

How do we tune in to the LOC and glidepath on an ILS?

Answer 6

We tune to the LOC and get the glideslope automatically

This reduces workload and errors

Question 7

What is a precision approach?

Answer 7

One where both azimuth and vertical position guidance is given

Question 8

What is a non precision approach?

Answer 8

One where azimuth guidance is given but not vertical position.

Instead a minimum descent height/altitude will be given

Question 9

How does a LOC work?

Answer 9

Generates 2 lobes at different AM:

Left lobe 90Hz AM

Right lobe 150Hz AM

The centerline is equisignal from both.

The principle of operation is Difference in Depth Modulation (DDM) or lobe comparison.

Question 10

How does a glideslope/path work?

Answer 10

2 lobes generated both AM.

Upper 90Hz AM

Lower 150Hz AM

Path where equisignal from both.

Principle of operation is DDM

Question 11

What is the coverage of a LOC?

Answer 11

35deg either side of centerline up to 17nm

10deg either side up to 25nm

up to 6250ft

Question 12

What is the coverage of a glidepath?

Answer 12

0.45 of glide angle to 1.75 of glide angle

Question 13

What frequency do ILS markers operate on?

Answer 13

75MHz

Question 14

What are the colours, pitch, ident and touchdown range for the different ILS markers?

Answer 14

Outer:

Blue; low; 2 dashes/s; 6.5 - 11.1km

Middle:

Amber; medium; alternate dashes and dots, 3/s; 1050m +/- 150m

Inner:

White; high; 6 dots/s; 75 - 450m

Question 15

What are the different ILS categories with ground installation and aircraft minima?

Answer 15

CAT 1 - ground installation = 60m above touchdown;

aircraft minima = 200ft on altimeter, RVR 550m.

CAT 2 = Ground installation = 15m above threshold;

aircraft minima = 100ft on radio altimeter, RVR 300m

CAT 3 = ground installation touchdown and beyond;

aircraft minima = 0ft on radio altimeter

A = RVR 200m

B = RVR 75m

C = RVR 0m

Question 16

What is the ILS critical area?

Answer 16

The area surrounding the glidepath antenna where movement of people and vehicles is forbidden.

Question 17

What is the ILS senstive area?

Answer 17

The area aroud the glidepath antenna where, during CAT 2 or 3 operations, movement of people and vehicles is restricted.

Question 18

What is the ILS back course?

Answer 18

Side lobes are created by the main antenna which cause a mirror image behind.

This mirror image causes reverse indication from behind.

Question 19

How can an ILS back course be flown?

Answer 19

Using HSI with reverse HDG in order to reverse the reversed information

Question 20

What are false glide slopes and how do we overcome them?

Answer 20

Glide slopes that are caused by the side lobes created by the main ILS system.

to overcome this we always intercept the correct glide slope from below

Question 21

What are the features of an ILS instrument display - OBI?

Answer 21

There are 2 break lines for horizontal (LOC) and vertical (glideslope)

the full scale LOC deviation is 2.5deg

the full scale glide slope deviation is 0.7deg

Failure flags flip when:

• there is significant distortion of radiation pattern
• the A/C flies out of the ILS service area
• Ground or airborn equipment fails or is turned off.

Question 22

What is the required accuracy that the pilot has to fly for an ILS approach?

Answer 22

within 1/2 scale deviation from desired track.

Question 23

Within what deviation from the LOC centerline does an A/C have to be before starting the descent onto the glide path?

Answer 23

1/2 full scale deviation.

Question 24

To remain within protected airspace what glidepath deviation must the pilot remain within?

Answer 24

1/2 full scale deviation.

Question 25

What happens to deviation sensitivity as you get closer to the LOC?

Answer 25

It gets more sensitive

Question 26

What errors are associated with ILS?

Answer 26

Beam bending from ground reflection

Scalloping reflection

Beam noise, distorting the beam

Commerical radios, FM interference

Siting error

Question 27

What are the disadvantages of ILS?

Answer 27

Only striaght approach

Only 1 glide path

Snow on aerial can affect the signal

Only 40 channels