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Aviation Sri Lanka 

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Communication

 
The VHF aeronautical communications band lies between 108.000 MHz and 136.975 MHz. (Recent expansion of the VHF aeronautical band has taken the upper limit from 135.975 to 136.975. At this time not all aircraft radios or consumer receivers are capable of tuning this expanded spectrum). This frequency spectrum can be divided into a lower and upper range. The lower range between 108.000 MHz and 118.000 MHz is primarily used for navigational aids such as the ILS - Instrument Landing Systems, DME - Distance Measuring Equipment, and VOR's - Very High Frequency Omni Range. The lower range offers very little in the way of voice communications, it does however provide someone with a working knowledge of Morse code the opportunity to identify various beacons. The upper range of the aeronautical band 118.000 MHz to 136.975 MHz is where the majority of voice communications can be monitored. Communications in the VHF band are transmitted in AM mode and most if not all compatible receivers automatically default to this mode. Frequencies within the aeronautical range are spaced in increments of 25 kHz, as such you will find transmissions at 118.000, 118.025, 118.050 MHz etc.

The UHF aeronautical band is located between 225.000 MHz and 400.000 MHz and is primarily used for military traffic. In the early years the Canadian military was responsible for patrolling the DEW (Distant Early Warning) Line for foreign invasions. As UHF was the only system in use at the time it has become the mainstay. Many commercially available receivers are not capable of tuning this frequency range and therefore this offers some form of security. Air traffic control facilities are equipped to transmit on both the VHF and UHF frequency simultaneously. This method of transmission allows a person whose receiver in unable to tune the UHF frequency the benefit of hearing at least one side of the conversation. The key is to monitor a parallel VHF frequency for the designated UHF frequency.

The frequency(s) you monitor will determine the nature of traffic you will hear. As previously mentioned, frequencies in the lower range of the aeronautical band are mostly occupied by navigational equipment and transmit non voice signals in Morse code. If you select a frequency in the upper range the air is suddenly filled with conversations between pilots and air traffic controllers, pilots and their company dispatchers, flight service stations, and ATIS broadcasts. Depending on your geographical location it is also possible to hear aircraft under the control of a facility in another Province, or for those living near the Canadian/USA border an American state. Frequencies within the aeronautical band are designated according to their usage. The following frequency allotment chart will give you an idea of where to locate the traffic that most interests you.

Frequency Range:

Communications Usage:

108.000 - 117.975 MHz

Navigational Aids

118.000 - 121.400 MHz

Control Towers

121.500 MHz

Int'l VHF Frequency

121.600 - 122.900 MHz

Ground & Apron Control

122.700 - 123.900 MHz

UNICOM Frequencies

123.450 MHz

Air to Air / Pilot chit chat

124.000 - 128.800 MHz

Arrivals & Departures

128.825 - 132.000 MHz

Company Operations

132.000 - 135.975 MHz

Area Control Centre (Enroute)

136.000 - 136.975 MHz

Shared ATC/Company Ops & DataLink

While efforts are made to maintain this arrangement, neighboring stations may interfere with one another and certain stations may be assigned a frequency outside of this designation.

There are no rules as to what time of the day is best, however each airport does have it's own peak periods. Based on traffic patterns at Pearson International Airport in Toronto, the busiest times occur between 7 and 9 AM, and 4 to 7 PM. The radio may seem very quiet during the overnight hours at your local airport this however does not necessarily mean there is nothing to hear. Monitoring the enroute (ACC) frequencies can often reward you with traffic from aircraft that have departed from a distant airport and that are overhead on their way to a city many miles away.

In order to monitor VHF & UHF aeronautical communications you must have a receiver, more commonly referred to as a scanner, that is capable of tuning between 108.000 to 136.975 MHz and 225.000 to 400.000 MHz respectively. As there are many models to choose from when selecting a receiver the best bet is to first choose one suitable to your budget. Once you are familiar with your new found hobby, purchasing an upgraded radio is an easy transition. Depending on the radio you have purchased the antenna type, if supplied, will vary considerably. This too can be upgraded by purchasing an antenna that performs better for the aeronautical bands. Generally if you live within 40 kilometers of an airport you should be able to hear ground communications, however geographic obstructions such as tall buildings or big hills can hamper your reception. Since VHF & UHF signals are received by line of sight, signals from airborne aircraft tend to be a lot clearer. A good philosophy for optimum antenna performance is "the higher the better". A couple of other useful resources to have while monitoring aeronautical communications would be aviation charts and a base map of your local airfield. With these aeronautical charts you will now be able to plot the course of the aircraft you are hearing. Similarly a base map of your local airfield will allow you to see and follow the route aircraft use between the runways and parking areas.

During radio transmissions letters and numbers can become difficult to understand and may be confused with one another. To avoid any confusion the Phonetic alphabet is use when pronouncing letters. Numbers too are pronounced slightly different thus eliminating any confusion.

A - Alpha

N - November

0 - Zero

B - Bravo

O - Oscar

1 - Wun

C - Charlie

P - Papa

2 - Too

D - Delta

Q - Quebec

3 - Tree

E - Echo

R - Romeo

4 - Fower

F - Foxtrot

S - Sierra

5 - Fife

G - Golf

T - Tango

6 - Six

H - Hotel

U - Uniform

7 - Seven

I - India

V - Victor

8 - Ait

J - Juliet

W - Whiskey

9 - Niner

K - Kilo

X - Xray

Decimal - DAY-SEE-MAL

L - Lima

Y - Yankee

Hundred - HUN-dred

M - Mike

Z - Zulu

Thousand - TOU SAND

UTC or Coordinated Universal Time is used in aeronautical communications to eliminate confusion between AM and PM. This can be critical especially to flights that cross many time zones. To calculate UTC, convert your local time to the 24 hour clock ex; 0100 = 1 AM, 0200 = 2 AM, 1200 = noon, 1300 = 1 PM, then add 4, 5, 6, or 7 hours for Eastern, Central, Mountain, or Pacific time respectively during daylight savings time. During standard time add 5, 6, 7, and 8 hours to your local 24 hour time.  

 

Altitudes are expressed in two different ways depending upon what altitude an aircraft is at. Altitudes at or below 18,000 feet are expressed in hundreds and thousands of feet, altitudes of 18,000 feet and above are referred to as flight levels. The following show how altitudes are expressed over the radio:

bullet8,000 feet = Eight Thousand
bullet10,000 feet = One Zero Thousand
bullet14,600 feet = One Four Thousand, Six Hundred
bullet20,000 feet = Flight level Two Zero Zero
bullet27,000 feet = Flight level Two Seven Zero
bullet30,600 feet = Flight level Three Zero decimal Six

RADIO COMMUNICATION AND NAVI ATION 

Type of Nav-Aid

ID

Frequency / Channel

DVOR DME

KAT

112.7 MHz

ILS/LLZ

IKA

110.3 MHz

RUNWAY 22

 

 

ILS /GP

 

335.0 MHz

RUNWAY 22

 

 

ILS /DME

IKA

40X

RUNWAY 22

 

 

ILS/LLZ

IKW

109.9 MHz

RUNWAY 04

 

 

ILS /GP

 

333.8 MHz

RUNWAY 04

 

 

ILS /DME

IKW

36X

RUNWAY 04

 

 

RADAR

CMB

1260.0 MHz

RADAR

 

13415.0 MHz

OM

 

75 MHz

RUNWAY 22

 

 

NE-LOCATOR

CNL

315 KHz

RUNWAY 22

 

 

MM

 

75 MHz

RUNWAY 22

 

 

SW-MARKER

 

75 MHz

RUNWAY 04

 

 

SW-LOCATOR

ASL

330 KHz

RUNWAY 04

 

 

Following maps depict the flight routs over the Sri Lanka Flight Information Region (FIR) where by clicking them you can have larger view of them.