08 ILS Flashcards
The three main (ground) components of an ILS are:
Localiser (LOC). - Horizontal Azimuth
Glide path (GP). - Verticcal
Range information (markers or DME).
ILS VHF LOC frequencies are assigned between
108.0 – 111.975 MHz, using an odd number after the decimal.
LOC antenna
The LOC antenna is located on the runway centre-line extension, at the stop-end.
GP and LOC frequencies?
ILS UHF GP frequencies are paired with the LOC frequencies.
GP Frequencies are UHF 329.3MHz - 335Mhz automatically selected.
GP Antenna?
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.
GP path lateral coverage?
Glide path vertical coverage?
Always pick up GP from below.
Multiple each by the glide slope angle.
How is the LOC centreline determined?
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.
How is the GP centreline determined?
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.
GP glide slope angle?
The recommended GP is 3° above the horizontal.
How does the AC reciicver calculate the angular deviation?
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.
Side lobes?
Both LOC and GP transmit side lobes which can cause false LOC and GP indications.
How is range provided?
Range may be provided by DME or by marker beacons
Use of marker beacons?
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.
Marker beacons are identified visually (cockpit lights) and audibly (Morse identification) as follows:
- 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.
The final-approach area?
The final-approach area contains a fix or facility (usually the outer marker or DME) that permits verification of the ILS GP – altimeter relationship.
LOC and GP monitoring?
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.
LOC and GP warning flags appear if:
- Received signal strength below threshold value.
- Carrier wave stops transmitting.
- Modulating signal stops transmitting.
- Modulating signal percentage power reduces to 0.
ILS readout?
0.5 - degrees per dot for LOC
0.15 - degrees per dot for GS
You need to remain within half full scale defelection.
Cockpit indications for ILS?
Cockpit indications are read on CDI or HSI (or electronic equivalent). The runway direction is set as the selected course.
Maximum (full-scale) deflection of the deviation bar, along respective scales are:
LOC — +/- 2.5°
GP — +/- 0.75°
Exceeding this means a missed approach is required.
The back beam?
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.
LOC plan coverage?
- 10° either side of centerline out to 25 NM.
- 35° either side of centerline out to 17 NM.
ILS facility accuracy requirements increase with performance category, which are:
CAT I
CAT II
CAT IIIA
CAT IIIB
CAT IIIC
The following apply to ILS approaches:
- 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.
ILS critical area
area around LOC and GP antennas where operations are prohibited during ILS operations.
ILS sensitive area
area around LOC and GP antennas where operations are controlled during ILS operations.
ILS beam bends
deviations from nominal LOC and GP centrelines, which can be assessed.
Interference with LOC and signals
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.
Type of Approachs according to ICAO?
ICAO Annex 6
Type A - Min DH at or above 250ft due to obstacle clearence.
Type B - Min DH below 250ft
Glide path accuracy
- 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).
Localiser DDM?
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
Calcualtign heights and RoD
300ft per nm
or
1 in 60 rule
Scalloping / beam bending?
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.
