ILS+Localizer+-+Operation+and+Testing

= **__Warning__: This material is to be used for Training Reference only.****Always consult the Operations Maintenance Manual** = = = =**Instrument Landing System (ILS) - Localizer**=



Introduction:
The localizer is one the two main components of the instrument landing system (ILS), the other being the glideslope. The localizer system consists of 2 different modulated tones which are received and interpreted giving a reading on a VOR indicator which displays whether the course of the airplane needs to be corrected. When the bar is swung to the either side of the screen, it indicates that the plane must fly towards the indicated direction to align itself with its proper angle for the landing approach.

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Frequencies:
The localizer transmits in the VHF frequency range that is used by the VOR system (108-112 MHz.). The two systems are kept separate by the allocation of their relative frequencies within that spectrum.

Two modulated signals are transmitted on any one of the ILS channels. The first is modulated at 90 Hz, while the other is modulated at 150 Hz and these are transmitted from separate but co-located antennas. Each antenna transmits a narrow beam, one slightly to the left of the runway centerline, the other to the right. The localizer receiver on the aircraft measures the difference in the depth of modulation (DDM) of the 90 Hz and 150 Hz signals. For the localizer, the depth of modulation for each of the modulating frequencies is 20 percent. The difference between the two signals varies depending on the position of the approaching aircraft from the centerline.
 * ~ LOC ||~ VOR ||
 * =  ||= 108.000 MHz ||
 * = 108.100 MHz ||=  ||
 * = 108.150 MHz ||=  ||
 * =  ||= 108.200 MHz ||
 * = 108.300 MHz ||=  ||
 * = 108.350 MHz ||=  ||
 * =  ||= 108.400 MHz ||
 * = 108.500 MHz ||=  ||
 * = 108.550 MHz ||=  ||
 * =  ||= 108.600 MHz ||
 * = 108.700 MHz ||=  ||
 * = 108.750 MHz ||=  ||
 * ~ Example ||~ alignment ||

====**Air Equipment**: Antennas for the Localizer are typically paired with the VOR antennas and are of the Di-Pole variety. They need to installed as such that they remain horizontal ensuring proper alignment with the transmitted radio signals.====

[[image:http://www.transair.co.uk/products/images/large/commant_CI157P_antenna.jpg width="303" height="232"]]
====**Ground Equipment**: Antennas for the ILS Localizer system are located directly in line with the runway and usually a 1000 feet behind it. A signal is developed behind the ILS transmitter that is often of use. This is known as the back-course. It can be used for a localizer approach but the signal will be inverted. Some Nav systems installed on planes will convert the signal automatically while others will not.====



Procedures/Parameters: No Bench Procedures could be found online. Always consult the manual for the individual systems test procedures.

 * ~ Tone Difference Values ||~  ||~   ||~   ||~ Course Deviation Indicator ||
 * ~ 90 and 150 Hz % Mod. ||~ DDM ||~ Decibels ||~ Deflection ||~ Microamps ||
 * = 20.00, 20.00 ||= 0 ||= 0 ||= Centered ||= 0 ||
 * = 15.35, 24.65 ||= .093 ||= 4.114 ||= Standard ||= 90 ||
 * = 12.25, 27.75 ||= .155 ||= 7.102 ||= Full Scale ||= 150 ||
 * = 10.00, 30.00 ||= .200 ||= 9.542 ||= + Full Scale ||= 194 ||
 * = 0.00, 40.00 ||= .4 ||= Infinity ||= Full tone delete other ||= 387 ||

References:
1. http://en.wikipedia.org/wiki/Instrument_landing_system 2. http://www.navfltsm.addr.com/ils.htm 3. Assorted ILS handouts provided in-class by the Instructor. Christopher