What is the difference between precision approaches and non-precision approaches?
Precision - Azimuth and glideslope guidance
Non-precision - Azimuth only
What is the principle of ILS?
Lobe comparison
What signals are compared in the equipment to give an indication of deviation from a centre line in azimuth?
Difference in depth of modulation of a 150 Hz and a 90 Hz modulation
When on the approach, where should the 90 Hz signal be on ILS only?
On the left
When on the approach, what is the frequency of the lower lobe in G/S?
150 Hz
What are the range of spot frequencies of the localiser?
108.1 MHz to 111.95 MHz
Besides the 90 Hz and 150 Hz lobes, what else does the localiser radiate?
A Morse identifier of 2 or 3 letters, at 1020 Hz, transmitted 6 times a minute
What is an offset localiser?
Site constraints have prevented the localiser from being placed in the normal plane with the runway
The coverage pattern of the localiser is achieved by doing what?
Combining two separate radiation patterns
Describe the course radiation pattern?
Extends 10° either side of the centre line to a distance of 25 nm from the localiser
Describe the clearance pattern?
Extends coverage of the localiser to 35° to either side of the course line to a distance of 17 nm from the localiser
Describe the G/S pattern?
8° either side of the runway to a distance of 10 nm from the runway, angled at between 2° and 4°
What frequency do the marker beacons of the ILS facility operate on?
75 MHz
Describe the marker frequencies and lights?
Outer - 400 Hz, blue
Middle - 1300 Hz, amber
Inner - 3000 Hz, white
What is the frequency band of VOR?
108 MHz to 118 MHz
What is the great advantage of VOR over ADF?
It does not suffer from night effect
What type of modulation is utilised for the reference signal and the directional signals in VOR?
Reference - FM 30 Hz
Directional - AM 30 Hz
What does the TO/FROM circuit in the navigation unit do for VOR?
Senses the cosine output from the Omni-Bearing Selector and causes the appropriate flag to be displayed on the OBS
Describe a category A VOR?
- 112 MHz to 117.95 MHz
- Used for normal en route navigation
- 200 W output
- 200 nm
- 120 channels
Describe a category B VOR?
- 108 MHz to 111.95 MHz
- Used for approach and let down information
- 50 W
- 25 nm
- 40 channels
In VOR, why is FM and AM used with wide frequency separation between them?
Prevents cross modulation between the signals which would otherwise cause bearing errors in the system
What is the ‘cone of confusion’ of VOR?
At 40° elevation above a beacon, there is a coned area where the indications are characterised by violent fluctuations
What is the polarisation of a VOR signal?
Horizontal
Which signal in VOR is said to lag the other?
Variable signal (directional) is said to lag the reference phase (omni-directional)
