08 ILS

Question 1

The three main (ground) components of an ILS are:

Answer 1

Localiser (LOC). - Horizontal Azimuth
Glide path (GP). - Verticcal
Range information (markers or DME).

Question 2

ILS VHF LOC frequencies are assigned between

Answer 2

108.0 – 111.975 MHz, using an odd number after the decimal.

Question 3

LOC antenna

Answer 3

The LOC antenna is located on the runway centre-line extension, at the stop-end.

Question 4

GP and LOC frequencies?

Answer 4

ILS UHF GP frequencies are paired with the LOC frequencies.

GP Frequencies are UHF 329.3MHz - 335Mhz automatically selected.

Question 5

GP Antenna?

Answer 5

The GP antenna should be located beyond the runway threshold, laterally displaced to the side of the runway edge.

On aircraft it is in the nose.

Question 6

GP path lateral coverage?

Answer 6

Question 7

Glide path vertical coverage?

Answer 7

Always pick up GP from below.

Multiple each by the glide slope angle.

Question 8

How is the LOC centreline determined?

Answer 8

The LOC centreline is determined by two overlapping left and right beams (lobes), AM modulated at 90 Hz(Left Yellow) and 150 Hz (Right Blue) respectively.

Question 9

How is the GP centreline determined?

Answer 9

The GP is determined by two overlapping upper and lower beams (lobes), AM modulated at 90 Hz (Upper, Yellow) and 150 Hz(Lower, Blue) respectively.

Question 10

GP glide slope angle?

Answer 10

The recommended GP is 3° above the horizontal.

Question 11

How does the AC reciicver calculate the angular deviation?

Answer 11

The aircraft receiver calculates angular deviation from LOC centreline and GP by measuring the difference in depth of modulation of each lobe.

The depth of modulation is at a minimum in the centre.

Question 12

Side lobes?

Answer 12

Both LOC and GP transmit side lobes which can cause false LOC and GP indications.

Question 13

How is range provided?

Answer 13

Range may be provided by DME or by marker beacons

Question 14

Use of marker beacons?

Answer 14

Marker beacons produce vertical 75 MHz VHF radiation patterns to indicate predetermined distances from the runway threshold along the ILS GP.

Features 2 or 3 letter Morse code ident.

Question 15

Marker beacons are identified visually (cockpit lights) and audibly (Morse identification) as follows:

Answer 15

• Outer marker — Blue — two dashes per second at low frequency. This marker normally indicates the Final Approach Fix (FAF). It is located between 4 and 7 nm.
• Middle marker — Amber — continuous alternating dots and dashes at medium frequency. This marker normally indicates the CAT I Missed approach point and it is positioned between 0.5 and 0.8 nm from the runway threshold.
• Inner marker — White — six dots per second at high frequency.

Question 16

The final-approach area?

Answer 16

The final-approach area contains a fix or facility (usually the outer marker or DME) that permits verification of the ILS GP – altimeter relationship.

Question 17

LOC and GP monitoring?

Answer 17

LOC and GP have automatic monitoring system, which monitors any shift in the LOC and/or GP mean course line, or reduction in signal strength.

Question 18

LOC and GP warning flags appear if:

Answer 18

• Received signal strength below threshold value.
• Carrier wave stops transmitting.
• Modulating signal stops transmitting.
• Modulating signal percentage power reduces to 0.

Question 19

ILS readout?

Answer 19

0.5 - degrees per dot for LOC
0.15 - degrees per dot for GS

You need to remain within half full scale defelection.

Question 20

Cockpit indications for ILS?

Answer 20

Cockpit indications are read on CDI or HSI (or electronic equivalent). The runway direction is set as the selected course.

Question 21

Maximum (full-scale) deflection of the deviation bar, along respective scales are:

Answer 21

LOC — +/- 2.5°
GP — +/- 0.75°

Exceeding this means a missed approach is required.

Question 22

The back beam?

Answer 22

The back beam from the LOC antenna may be used as a published ‘non-precision approach’.

The LOC back beam can give reverse sensing indications on cockpit instruments.

Correct sensing can be obtained when flying a LOC back beam, by using an HSI with the front course set (ILS QDM), instead of the back course.

OBI’s cannot be corrected.

No GS - Non precicion approach.

Question 23

LOC plan coverage?

Answer 23

• 10° either side of centerline out to 25 NM.
• 35° either side of centerline out to 17 NM.

Question 24

ILS facility accuracy requirements increase with performance category, which are:

Answer 24

CAT I
CAT II
CAT IIIA
CAT IIIB
CAT IIIC

Question 25

The following apply to ILS approaches:

Answer 25

• An aircraft has to be established on the LOC before it can descend on the GP.
• An aircraft is established on the LOC if the CDI/HSI is within half-scale deflection.
• The aircraft must be within half-scale fly-up deflection of the GP to remain within protected airspace.

Question 26

ILS critical area

Answer 26

area around LOC and GP antennas where operations are prohibited during ILS operations.

Question 27

ILS sensitive area

Answer 27

area around LOC and GP antennas where operations are controlled during ILS operations.

Question 28

ILS beam bends

Answer 28

deviations from nominal LOC and GP centrelines, which can be assessed.

Question 29

Interference with LOC and signals

Answer 29

Objects reflecting LOC and GP signals cause multipath interference. Normally due to aircraft moving around near the ILS antennas.

Scolloping - continous bending to and from down the ILS.
Beam bending - constant bending of the beam.

FM interfenece just below 108Mhz - Affects Localiser only as VHF, not if the aircraft is fitted with an immunity filter.

Question 30

Type of Approachs according to ICAO?

Answer 30

ICAO Annex 6

Type A - Min DH at or above 250ft due to obstacle clearence.
Type B - Min DH below 250ft

Question 31

Glide path accuracy

Answer 31

• I can give accurate guidance down to a height of 100 ft or less
• category II down to 50 ft or less
• category III down to the runway (with the aid of ancillary equipment).

Question 32

Localiser DDM?

Answer 32

The Difference in Depth of Modulation (DDM) will vary proportionally and linearly with the angular displacement of the aircraft from the extended runway centerline.
DDM = AM (90 hz) - AM (150 hz) / 100

Question 33

Calcualtign heights and RoD

Answer 33

300ft per nm

or

1 in 60 rule

Question 34

Scalloping / beam bending?

Answer 34

Rapid changes either side of the approach path that cannot be followed by the aircraft.

Describe ILS beam bends as deviations from the nominal LOC and GP respectively which can be assessed by flight test.