1. AIRPORTS AUTHORITY OF INDIA
REGIONAL TRAINING CENTER (CNS),ER
A Project Report On winter Vocational Training in-
Communication, Navigation and Surveillance (CNS)
Electronics & Communication Engineering - B.Tech – 3rd
HERITAGE INSTITUTE OF TECHNOLOGY
This is to certify that Akash Chowdhury, a student of 3rd year in Electronics
and Communication Engineering (BTECH) from Heritage Institute of
Technology, has completed his Winter Vocational Training on Communication
Navigation and Surveillance (CNS) at Airports Authority of India, Regional
Training Centre (CNS), Eastern Region, Netaji Subhash Chandra Bose
International Airport, Kolkata from 4th
January, 2016 to 15th
Signature of Training Coordinator
(Shri. Samir Kumar Mukhopadhyay)
Assistant General Manager (CNS)
3. STUDENT'S DECLARATION
I hereby declare that I, Shri. Akash Chowdhury has completed my winter
vocational training on COMMUNICATION, NAVIGATION AND SURVEILLANCE
(CNS) and submitted my project report to Regional Training Centre (CNS),
Eastern Region, Airports Authority of India, NSCBI Airport, Kolkata on the
completion of the same from 4th
January to 15th
To the best of my knowledge, this project report has not been submitted for
any other examination and does not form a part of any other course
undergone by the candidate.
Signature of Student
Name of Student: AKASH CHOWDHURY
5. WEB BASED CONTROL............................................................... 48
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I take this opportunity to express my profound gratitudeand deep regards to my guide
Shri. S. Ghosh, General Manager (CNS) for their exemplary guidance, monitoring and
constantencouragement throughoutthis training. Sitting at the office of the airport and
listening to the lectures of the aircraft communication made us think that it was an easy
task to fly into the vastexpanse on COMMUNICATIONNAVIGATION &SURVEILLANCE
but it was only when we gathered knowledge about this topic, we realized how much
helpful were somepeople to us. Without them this exploration could never havebeen
I am obliged to the staff members at AAI of NSCBI airport, for the valuable information
provided by them in their respectivefields. I am grateful for their cooperation during the
period of my assignment.
RTC (CNS) ER
MR.Samir Kumar Mukhopadhyay, ASM(CNS)-RTC
MR.SantoshKumar Sinha (CNS)-RTC
MR.Samit Kr. Das,AGM(CNS)-HF TRANSMITTER
MR.S.K. Lahiri ,AGM(CNS)-CMU
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MR.Tapas Banerjee,AGM(CNS)-HF RECEIVER
MR.Gouri Shankar Ghosh,AGM(CNS)-COM BRIEFING
I take this opportunity to express my sinceregratitude to Prof. Dr.P.Banerjee, head of
the Electronics andCommunicationEngineering Department, Heritage Institute of
Technology, Kolkata, who gave the permission to be associated with one of the best
organisation, Airports Authority of India, NSCBI Airport, Kolkata.
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Airports Authority of India (AAI) was constituted by an Act of Parliament and
came into being on 1st April 1995 by merging erstwhile National Airports
Authority and International Airports Authority of India. The merger brought
into existence a single Organization entrusted with the responsibility of
creating, upgrading, maintaining and managing civil aviation infrastructure
both on the ground and air space in the country. It manages 133 airports and
covers 2.8 million square nautical miles area which includes oceanic area of
1.7 million square nautical miles.
During the year 2008-09, AAI handled aircraft movement of 1306532 nos.
[International 270345 & domestic 33785990] and the cargo handled 499418
tones [international 318242 & domestic 181176]. AAI provides CNS/ATM
services at all the civil airports in the country.The 133 airports managed by
AAI includes 16 international,8 custom,24 civil enclaves and 80 domestic
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FUNCTIONS OF AAI
The functions of AAI are as follows:
Design, Development, Operation and Maintenance of international and domestic airports and
Control and Management of the Indian airspace extending beyond the territorial limits of the
country, as accepted by ICAO.
Construction, Modification and Management of passenger terminals.
Development and Management of cargo terminals at international and domestic airports.
Provision of passenger facilities and information systemat the passenger terminals at airports.
Expansion and strengthening of operation area, viz. Runways, Aprons, Taxiway etc.
Provision of visual aids.
Provision of Communication and Navigation aids, viz. ILS, DVOR, DME, Radar etc.
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Communication, Navigation and Surveillance are three main functions (domains) which constitute the
foundation of Air Traffic Management (ATM) infrastructure. The following provide further details about
relevant domains of CNS:
Communication is the process of sending, processing & receiving of information by electrical means. In
Radio communication, for the transmission information are first converted into electrical signals then
modulated with a carrier signal of high frequency, amplified up to a required level, converted into
electromagnetic waves & radiated in the space, with the help of antenna. For reception these
electromagnetic waves are converted to electrical signals, amplified, detected & reproduced in the
original form of information with the help of speaker. Communication is the exchange of voice and data
information between the pilot and air traffic controllers or flight information centres.
Fig: Block diagram representing transmitter & receiver
Frequencies band uses in Communication:
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NAME OF THE
FREQUENCY BEND USES
NDB 200-450 KHz Locator, Homing & En-
HF 3-30 MHz Ground to Ground/Air
Localizer 108-112 MHz Instrument Landing
VOR 108-117.975 MHz Terminal, Homing & En-
VHF 117.975-137 MHz Ground to Air
Glide Path 328-336 MHz Instrument Landing
DME 960-1215 MHz Measurement of Distance
UHF LINK 0.3-2.7 GHz Remote control,
RADAR 0.3-12 GHz Surveillance
Navigation Element of CNS/ATM Systems Is meant to provide Accurate, Reliable and Seamless Position
Determination Capability to aircrafts.
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The surveillance systems can be divided into two main types: - Dependent surveillance and Independent
surveillance. In dependent surveillance systems, aircraft position is determined on board and then
transmitted to ATC. The current voice position reporting is a dependent surveillance systems in which
the position of the aircraft is determined from on-board navigation equipment and then conveyed by
the pilot to ATC. Independent surveillance is a systemwhich measures aircraft position from the ground.
Current surveillance is either based on voice position reporting or based on radar (primary surveillance
radar (PSR) or secondary surveillance radar (SSR)) which measures range and azimuth of aircraft from
the ground station.
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Communication is the specialized field concerned with the use of electronic devices and systems
for the acquisition or acceptance, processing, storage, display, analysis, protection, disposition,
and transfer of information. A constant exchange of information is necessary between the aircraft
and the base or Air Traffic Control centre. Communication systems consist of a number of
components that facilitate processing of the information, its transmission and corresponding
reception at the destination, and finally retrieval of the required message. With regards to the CNS
system, communication can be classified as:
Voice communication – it involves sending audio messages
Data communication – it involves sending messages in the form of texts
Voice communication is a direct form of communication and is hence a faster process than
data communication which involves processing time (leading to time delay).
There are two allotted band of frequencies which are used in communication for aviation
purpose. They are the High frequency (HF) band and the Very high frequency (VHF) band. The HF
band ranges from 3-30 MHz while VHF band ranges from 30-300 MHzFor aviation purposes the
preferred HF range is 3-12 MHz and for VHF the range between 118-136 MHz is preferred.
Transmission of information over free space takes place in the form of electromagnetic
radiation or light (in case of optic fibres).
High frequency (HF) radio provides aircraft with an effective means of communication overlong
distance oceanic and trans-polar routes. In addition, global data communication has recently been
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made possible using strategically located HF data link (HFDL) ground stations. HF communication is
preferred in cases where VHF communication is not possible.
Characteristics of HF Communication:
HF follows Sky-wave propagation (involves total internal reflection of the HF signal in the
It is used mainly for long distance propagation beyond 200 nautical miles.
Bandwidth of HF Communication is in between 3MHz to 30 MHz, due to reflection from the
ionised layers in the upper atmosphere. Due to variations in height and intensities of the ionised
regions, different frequencies are used at different times of day and night and for different
Polarisation is horizontal.
It has a wider range and is not affected by obstruction.
Between the transmitter and the receiver there is a considerable region of blind range, where no
signal is available. This distance is known as skip distance (Disadvantages of Sky Wave
HF communication does not have high noise immunity due to ionospheric interference.
HFRT is also used for ground to ground communication, although it being fast replaced by
satellite communication. ICAO provides specified group of frequencies between fixed stations of
the HF network.
Due to its wider coverage area, as we know, there are three types of Controls in aviation that
uses VHF. Beyond the Area Control the use of VHF is not possible. Hence for coverage of area
greater than 250NM from the ATC, HF communication is used. This is more prevalent in place
where the aircraft is passing over sea area and communication between ATC and aircraft has to
In HFRT communication, HF controller controls the aircraft as well as communicates with the
Area/Flight Information Centre, to provide aircraft position and flight levels.
Also, HFRT is used for control of VVIP flights from departure airport to destination airport.
In flight control each significant position is given a five alphabet name. Example- MABUL, RINDA,
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This stands for Major World Air Route Area. It is exclusively used for providing International flights to
provide information such as position reports, met reports, flight level clearance, etc. The available
frequencies for MAWARA at Netaji Subhash Chandra Bose International Airport at Kolkata are:-
c. 3491 KHz
Among these, the 1st two are used during the day (1 is main, 1 is standby), and the other two at night.
This stands for Regional Domestic Air Route Area. These are a set of designated frequencies for HF
communication that are used to communicate with aircrafts to inform them about position, weather
conditions etc. The frequencies for RDARA at AAI Kolkata Airport are:-
Is an electronic device which, with the aid of an antenna, produces radio waves? The transmitter itself
generates a radio frequency alternating current, which is applied to the antenna. When excited by this
alternating current, the antenna radiates radio waves. In addition to their use in broadcasting,
transmitters are necessary component parts of many electronic devices that communicate by radio,
such as cell phones,
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Wireless computer networks, two way radios in Aircraft, ship, spacecrafts, radar sets, navigational
In AAI Kolkata:-
Zenitel hf transmitters Model No.CST2002A having power output of 2.5KW are used for HFRT
The said Transmitters are highly modular & used in fully remote controlled. The equipment covers a
frequency range of 1.6MHz to 30MHz and offers simples, duplex and semi duplex radio operation.
All the transmitters are used as individual Server. From Radio operating position, remotely any one
transmitter can be selected for operation through UHF Link.
The transmitter contain four main blocks:-
i) The transmitter Control System (TCS )
ii) The digital frequency synthesizer (DFS )
iii) The high power Amplifier ( HPA )
iv) The power supplies
The TCS is based around two microcontroller modules i.e. the WEBLINK and the ADAM-5511. The ADAM
5511 controls the harmonic filter and the antenna matching unit and monitors the reflectometer
outputs, enables the HF power output.
The WEBLINK controls power on/off, of Fans, the DFS and the HPA parts, control and monitors
the ADAM-5511, the state of all HPA parts, DFS. It offers the human Machine Interface (HMI) to both the
Local user (via local monitor and keyboard) and the Remote User(s) via an Ethernet connection.
Generates a modulated low power hf signal according to the selection of the user (carrier frequency), LF
audio input, class of operation, power output level. The HF signal generation is fully digitized by the use
of DDS (Direct Digital Synthesis) technique.
a) Driver 1:- Supply voltage 24Vdc, Gain ±26db, Class A amplifier.
b) Driver 2:- Supply voltage 48Vdc, Gain ±17db, Class A amplifier.
c) Power amplifier: - Supply
voltage 48Vdc, Gain
±13.5db, Class AB
d) Reflectometers: -
Measures both Forward
and Reflected power
used for antenna
matching unit and
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e) Filters: - To eliminate the harmonics in the power output.
f) Matching unit: - Impedance matching for maximum RF power transfer and reduces the
transmitter load to a VSWR of maximum 1.5.
Fig: PA Unit
Conversion from balanced to unbalanced line, used before antenna.
Open ended broadband dipoles are used.
Fig: Block Diagram of HF Transmitter
Here, the transmitter uses a Digital Frequency Synthesizer (DFS) to generate the carrier frequency.
This DFS uses DDS technology. Direct Digital Synthesizer (DDS) is a type of frequency synthesizer used
for creating arbitrary waveforms from a single, fixed-frequency reference clock. Applications of DDS
include: signal generation, local oscillators in communication systems, function generators, mixers,
modulators, sound synthesizers and as part of a digital phase-locked loop.
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Fig: Direct Digital Synthesizer block diagram
A basic Direct Digital Synthesizer consists of a frequency reference (often a crystal or SAW oscillator), a
numerically controlled oscillator (NCO) and a digital-to-analog converter (DAC) as shown in Figure 1.
The reference provides a stable time base for the system and determines the frequency accuracy of
the DDS. It provides the clock to the NCO which produces at its output a discrete-time, quantized
version of the desired output waveform (often a sinusoid) whose period is controlled by the digital
word contained in the Frequency Control Register. The sampled, digital waveform is converted to an
analog waveform by the DAC. The output reconstruction filter rejects the spectral replicas produced
by the zero-order hold inherent in the analog conversion process.
A DDS has many advantages over its analog counterpart, the phase-locked loop (PLL), including much
better frequency agility, improved phase noise, and precise control of the output phase across
frequency switching transitions.
Yagi-Uda antenna is used to transmit from transmitter station to ATC at airport using UHF Link for line of
Fig: Block Diagram of Ethernet Protocol Operation
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HF stands for High Frequency. It operates on a range of 3 - 30 MHz HF operates at a range greater than
200NM. The wavelength of HF lies between a ranges of 100 - 10 meters.
Main parameters of any receiver:
It is the ability of any receiver to respond to a weak signal voltage and develop a standard output signal
from that low voltage. Higher the sensitivity of the receiver, greater amount of weak signals will be
picked up by the receiver.
It is the ability of any receiver to select a particular frequency or a band of frequencies while rejecting
the undesired ones. Selectivity increases with the no. of tuned circuits used.
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Here n indicates the no. of tuned circuits, the selectivity curve becomes narrower with increase in no. of
The tuned circuits used consist of two elements: inductor and capacitor.
It is a measure of the receiver's ability to reproduce the intelligence of a signal (it must reproduce as
faithful as the signal that is received).
The receiver used for HF communication is AM super heterodyne receiver.
• ICOM Receiver (made in Japan) is used in AAI, Kolkata. It is a wideband receiver. Its features are
• Frequency coverage is: 100 KHz to 1 GHz.
• It is a multipurpose receiver with different modes :
• Upper Side Band.
• Lower Side Band.
• Continuous Wave.
• Frequency Shift Keying.
• Amplitude Modulation.
• Narrow Band Frequency Modulation.
• Wide Band Frequency Modulation.
• Receiver type: Super heterodyne system.
• Sensitivity: 2µV. This is the minimum voltage that can be detected by the receiver.
• Audio Output Impedance: 4 to 16 ohms.
Some frequencies of HF communication for Calcutta airport are 3491 KHz, 5471 KHz, 6556 KHz and
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VHF stands for Very High Frequency Communication. It is the most common means of airborne
communication. VHF Communication System consists of VHF transmitter, receiver, Transceiver
handset, control head, antenna and an interface to the aircraft audio system for access to the
microphone or cockpit speaker.
Characteristics of VHF Communication:
VHF follows Line of Sight Communication or Point to Point Communication. Since the
transmission is line of sight, the range depends on altitude of the aircraft and ground station.
VHF communication is used for short distance communication.
Frequency range of VHF Communication is in between 30 MHz and 300 MHz
VHF Communication is a Noise free communication.
As per ICAO, frequency range for AMS (Aeronautical Mobile Service) allotted 118 MHz to
136.975 MHz (for aviation purpose).
Range of VHF is 200 nautical miles.
In light aircraft, transceiver is mounted in the instrument panel and contains all the necessary
controls and displays.
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In larger aircraft the control head which is used for selecting the receiver and transmitter
frequencies is usually located in the centre console between the pilot and co-pilot, transceiver is
remotely located in the radio rack.
VSWR (Voltage Standing Wave Ratio) for VHF is 1.05.
PARK AIR T6T 50 WATT VHF (IP Base) Transmitter is intended for use in fixed ground environments
such as airports and en-route centres.
Transmitters are used for Voice Communication between Air traffic controller and pilot of aircraft
and vice versa.
Power Output of VHF Transmitter: 50 Watt.
Modulation Technique used for VHF transmitter is AM (Amplitude Modulation).
Polarisation: Vertical Polarisation.
Propagation: Line of Sight
Type of antenna used : Folded Dipole
Cable used for connecting transmitter with antenna: Co- axial RF cable (impedance 50 ohm).
Power Supply: 230 volt AC or 24 volt DC normally
Transmitter can store frequency in its channel memory, Frequency accuracy better than 1PPM.
Environmental: Temperature range -20 degree to +55 degree.
Duty cycle 100% continuous operation.
Channel Spacing: 25 KHz/ 8.33 KHz.
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Transmitting 500 VA 12 Amp
Ideal Mode 6 VA 1 Amp
Transmitter is tuned at the same time and at the same frequency as the receiver.
Offset Carrier System: It is a systemwhich helps to connect the transmitter of another station when
the signal strength is poor in the base station.
Accessories: VEP maintenance application and a VoIP configurator application is supplied.
Connecting to Control equipment: 4 wire audio and PTT using analogue lines, E1 Link, Ethernet links.
In Airports Authority of India presently Kolkata Airport using IP based Voice Communication System
and here IP based TX/Rx are used and it is the first time in India as well as in Asia.
Fig: Block Diagram of VHF Transmitter
A.A.I operates in 118MHz to 136.975MHz.It is a type of Line of Sight Communication.3 basic
components required for VHF communication are transmitter, receiver and antenna.
VHF transmitter have two transmitters in a single equipment. One transmitter is on air while other is on
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VHF receiver have two receivers in a single equipment. One receiver is on air while other is on Standby.
The antennas used for transmission are Directive antenna and Omni directional antenna.
VHF Receiver has the function of selecting the desired signal at VHF frequencies from all the other
unwanted signal amplifying and demodulating it, and reproducing it in the actual shape or desired
manner. It helps to receive the signals transmitted from another transmitter.
Fig: Block Diagram of VHF Transmitter
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SWITCHING SYSTEM (AMSS)
AMSS is a computer based system, centred on the Aeronautical Fixed Telecommunication Network
(AFTN) for exchange of Aeronautical messages by means of auto-switching for distribution of messages
to its destination(s). This system works on store and forward principle.
AMSS is an acronym for Automatic Message Switching System. It has four major areas:
AMSS is a dual architecture computer based system which consists of few servers and workstations
which are linked to each other over a local area network as well as other equipment/devices for data
AMSS is mainly for exchange of AFTN messages, but at the same time AMSS can handle some non-
AFTN messages like AMS messages (formally known as HFRT/Radio messages).
AMSS receives the messages from the terminals connected via other switches, and after analysing,
stores the messages as well as automatically retransmits the messages to their destination. During the
above process it uses switching system, which allows on demand basis the connection of any
combination of source and sink stations. AFTN switching system can be classified into three major
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So far as automation is considered for any system, it could be achieved by means of mechanical
devices like relay etc. and/or application software design as per requirement. In Electronics
Corporation of India Limited (ECIL) AMSS, maximum features of automation like message switching,
analysing, storing, periodical statistics etc. are taken care of by AMSS software and few means of
AMSS consists of three major components:
It incorporates communication adapters, protocols/suites, routing and gateway facilities. The core
system is composed of two identical computer machines (known as AMSS main servers) which run in an
operational/hot standby combination. Both units supervise each other‘s software and hardware
It has two identical mass data storage devices for storing of all incoming and outgoing AFTN messages. It
also has two identical mirrored Database servers which are operated in parallel. The mirroring between
the two database servers is performed in the background to store specified type messages like NOTAM,
MET, ATC, HFRT, with no effect on the regular operation.
It is the interface between user and the system with capability for uniform administration and
monitoring facilities for all system components, networks and data as well as exchange of data as per
requirement of users vide different type application software. Any number of user terminals (maximum
60) can be installed and used simultaneously.
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AFTN (AERONAUTICAL FIXED
The Aeronautical Fixed Telecommunication Network (AFTN) is a worldwide system of aeronautical
fixed circuits provided, as part of the Aeronautical Fixed Service, for the exchange of various
Aeronautical Messages and/or digital data between aeronautical fixed stations having the same or
compatible communications characteristics which is necessary for ensuring safety of air navigation
and the regularity of air traffic between aeronautical fixed stations of different states and between
Type of Messages.
DISTRESS MESSAGES ( priority indicator SS ).
URGENCY MESSAGES ( priority indicator DD ).
FLIGHT SAFETY MESSAGES: ( priority indicator FF ) [FPL-Flight Plan, DEP-Departure, ARR-
METEOROLOGICAL MESSAGES : ( priority indicator GG ) [1. Messages concerning forecast e.g.
terminal aerodrome forecasts (TAFs), area and route forecasts. 2. Messages concerning Weather
observations and reports of Aerodrome e.g. METAR, SPECI.]
FLIGHT REGULARITY MESSAGES.
AERONAUTICAL ADMINISTRATIVE MESSAGES.
NOTAM MESSAGES (Priority indicator GG).
The message format of AFTN messages is defined in ICAO Annex 10 Aeronautical
Telecommunications Volume II.
Example of AFTN message format ( FPL-Flight Plan) message:
ZCZC AEA0129 050358
FF VECFZQZX VIDFZQZX VILKZTZX
-N0514F320 L507 CEA R460 TEPAL R460 LLK R460W
-VIDP 0330 VILK
-EET/VYYF0025 VECF0122 VGFR0134 VECF0146 VIDF0130 REG/VTEFG SEL/DHGR
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DAT/SV RMK/TCAS EQUIPPED NAV/JRNAV DOF/160105)
First Line represent the Heading of the message in which ZCZC is the Start-of-Message Signal,
AEA0129 refers to the Transmission Identification and 050358 is an Additional Service Indication
indicate Date and time of Transmission of the message.
Second Line represent Address consists of Two letter Priority Indicator (here it is FF), eight-letter group
Addressee Indicators (here it is Delhi ATC, Lucknow ATC and Kolkata ATC). (Maximum 21 Addressee
Indicators in 3 Address Line can be used for single message).
Third Line represent the Origin of the message consists of message Filing Time (six-digit date-time-
group), the Originator Indicator (eight-letter group-Location Indicator & Unit, here it is Bangkok ATC
Next part (Here Fourth to Tenth Lines) represent the Message Text. Here it is a Text of FPL
message. (When a text is exceeding 1800 characters, the message is divided into two or more
Last Line/Last part is the Ending of the message is indicated by NNNN which is the End-of-Message
(Text of the Message will contain ZCZC or NNNN).
DECODE of above FPL message:
FPL- Message Type, AIC67-Aircarft Identification AIRINDIA67 , IS – Flight Rules(IFR) & Flight
B744/H-Aircraft Type (Boeing 744), H- Wake Turbulence(Heavy), SHIJDRYWZG/S-Equipment
VTBD1900-Departure Aerodrome Location Indicator (Bangkok) & Time (EOBT-Estimated Off
N0514- Cruising Speed, F320-Flight level , L507 CEA R460 TEPAL R460 LLK R460W-ATS Route.
VIDP0330- Destination Aerodrome(Delhi) & EET(Total Estimate Elapsed Time), VILK- Alternate
EET/VYYF0025 VECF0122 VGFR0134 VECF0146 VIDF0130 REG/VTEFG SEL/DHGR DAT/SV
RMK/TCAS EQUIPPED NAV/JRNAV DOF/160105-Other Information consist of EET of each FIRs,
Aircraft Registration(VTEFG),SELCAL CODE(DHGR), DOF(Date of Flight) etc.
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VOLMET (French origin VOL (flight) and METEO (weather)), or meteorological information for aircraft in
flight, is a worldwide network of radio stations that broadcast TAF, SIGMET and METAR reports
on shortwave frequencies, and in some countries on VHF too. Reports are sent in upper sideband mode,
using automated voice transmissions. Pilots on international routes use these transmissions to avoid
storms and turbulence, and to determine which procedures to use for descent, approach, and landing.
The VOLMET network divides the world into specific regions, and individual VOLMET stations in each
region broadcast weather reports for specific groups of air terminals in their region at specific times,
coordinating their transmission schedules so as not to interfere with one another. Schedules are
determined in intervals of five minutes, with one VOLMET station in each region broadcasting reports
for a fixed list of cities in each interval. These schedules repeat every half an hour.
The ranges used are:-
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The system operation is automatic, with no direct action by the pilot
The system’s accuracy is dependent on on-board navigation and other data sources (e.g. FMS) to provide
the data to be broadcast
The data is used for air and ground surveillance
Forms of ADS:-
ADS Contract (ADS-C)
The aircraft provides the information to the ground systemin four ways:
ADS Broadcast (ADS-B)
The data is broadcast. The originating aircraft has no knowledge of who receives and uses the data and
there is no 2-way ‘contract’ or interrogation
ADS-B is a surveillance application that involves a broadcast of position to multiple aircrafts or multiple
Each ADS-B equipped aircraft or ground vehicle periodically broad casts its position and other relevant
information derived from on board equipment.
ADS-B is currently defined for LOS operations (over VDL or Mode-S)
It can be used as alternative to ASDE
It has the potential to complement SSR.
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ADS B – Automatic Dependent Surveillance - Broadcast
Position Reports Position Reports
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CONTROLLER PILOT DATA LINK
A means of digital communication between controller and pilot, using data link instead of voice.
• Initial application for en-route operations in areas where the use of voice communication is
considered not efficient.
• CPDLC message have a standard formats, using familiar ICAO phrases.
• Before sending a CPDLC message, it can be viewed on the computer display unit and modified, if
Advantages of CPDLC over Voice Communications
• Significant reduction of workload for Pilot and Controller
• Alleviate voice channel congestion problems
• Allow ATC to handle more traffic
• Eliminate misunderstanding of poor voice quality
• Eliminate misinterpretation and corruption due simultaneous voice transmission
• Significant reduction of response time
• Automatic down linking a report such as way point crossing
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HFRT(HIGH FREQUENCY RADIO
High Frequency Radio Telephony ( voice communication) is a part of Aeronautical Mobile Service
reserved for air-ground communications between Pilots and Ground Controllers, related with the safety
and regularity of flights, flying primarily along national or international civil air routes. As VHF
coverage is insufficient due to range limitation to cover all portions of the routes flown, the use of HF
frequencies are necessary because they provide long range communications coverage over Thousand
In HFRT Network there are number of Aeronautical Stations to assist each other in order to provide the
air-ground communication service required of the network by aircraft flying on the air routes for which
the network is responsible.
In HFRT communication 2 frequencies are assigned to Aircrafts , one Higher frequency as
Primary and one Lower frequency as Secondary.
HFRT communication reception affected by Atmospheric noise because Transmission is through sky
On HFRT following categories of Aeronautical Messages are handled:
Distress, Urgency, Flight safety, Meteorological, Flight regularity.
Example of Aircraft Position Report Message:
AIC175 VABB-VECC POSITION NIPAD1105 FL350 EST KINKI1135 JJS NEXT SELCAL CODE
ATS Routes having number of reporting points which are many VOR codes like NNP. JJS etc and
number imaginary 5 letter name like NIPAD,KINKI, MABUR,URKOK etc (which are having fixed
HFRT STATION at NSCBI AIRPORT KOLKATA
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Equipment: HF Transmitter ( ZENETAL) with SELCAL Facility & Remote Radio Receiver (ICOM) &
ECIL AMSS workstation with ATC.
Language used: English
Hours of Operation: H24
Timings: In UTC
Call Sign: KOLKATA RADIO
HFRT NETWORK at Kolkata:
1. RDARA (Regional Domestic Air Route Area) for communication by Domestic Flights. Ground
stations are Kolkata, Chennai, Portblair, Delhi & Mumbai. Frequencies used are
2. MWARA (Major World Air Route Area) for communication by International Flights. Ground stations
are Kolkata, Dacca & Yangoon. Frequencies used are 10066,10051,6556,3491,2947KHz
In each Network one Frequency is maintained as Primary frequency and another frequency as Secondary
Higher frequencies are used during Day time and Lower frequencies are used during Night time.
VOLMET: ( Meteorological information for aircraft in flight ). Kolkata Radio broadcast VOLMET
Frequencies are 2965,6676,11387KHz. Broadcast time 5 minutes twice in every hour at interval of 30
minutes.(HR+05 to HR+10 , HR+35 to HR+40). Latest MET REPORT of KOLKATA, DACCA,
KATMANDU & YANGON are broadcasted.
VOLMET Stations in India are at MUMBAI(VABB) & KOLKATA(VECC)
Communication Procedure: As per ICAO ANNEX10 VOL II & other various Documents.
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International aviation, SELCAL is a selective-calling radio systemthat can alert an aircraft's
crew that a ground radio station wishes to communicate with the aircraft.
SELCAL uses a ground-based encoder and radio transmitter to broadcast an audio signal that
is picked up by a decoder and radio receiver on an aircraft.
The use of SELCAL allows an aircraft crew to be notified of incoming communications even
when the aircraft's radio has been muted. Thus, crewmembers need not devote their
attention to continuous radio listening.
When a SELCAL decoder on an aircraft receives a signal containing its own assigned SELCAL
code, it alerts the aircraft's crew by sounding a chime, activating a light, or both.
This uses DSB modulation technique.
ADVANCED SURFACE MOVEMENT
GUIDANCE AND CONTROL SYSTEM
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A-SMGCS (Advanced Surface Movement Guidance & Control System) is a system providing routing,
guidance and surveillance for the control of aircraft and vehicles in the runway or ground in order to
maintain the declared surface movement rate under all weather conditions within the aerodrome
visibility operational level while maintaining the required level of safety.
A-SMGCS is a modular system consisting of different functionalities to support the safe, orderly and
expeditious movement of aircraft and vehicles on aerodromes under all circumstances with respect to
traffic density and complexity of aerodrome layout, taking into account the demanded capacity under
various visibility conditions.
A-SMGCS consists of four basic functions:
Implementation of A-SMGCS defines 4 levels:
A-SMGCS Level 1
Improved Surveillance makes use of improved surveillance and procedures, covering the
manoeuvring area for ground vehicles and the movement area for aircraft. The procedures
concern identification and the issuance of ATC instructions and clearances. The controllers are
37. Page | 32
given traffic position and identity information which is an important step forward from the
traditional Surface Movement Radar (SMR) image.
A-SMGCS Level 2
Surveillance + Safety Nets adds safety nets which protect runways and designated areas and the
associated procedures. Appropriate alerts are generated for the controllers in case of conflicts
between all vehicles on runways and the incursionofaircraft onto designated restricted areas.
A-SMGCS Level 3
Conflict Detection involves the detection of all conflicts on the movement area as well as
improved guidance and planning for use by controllers.
A-SMGCS Level 4
Conflict Resolution, Automatic Planning & Guidance provides resolutions for all conflicts and
automatic planning and automatic guidance for the pilots as well as the controllers.
Fig: ASMGCS Layout of Runway
RADAR is an acronymcoined by the US Navy from the words Radio Detection and
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Radar is basically a means for gathering information about distant objects called “targets”
by sending electromagnetic waves at them and analysing the returns called the “echoes”.
Types of Radar:-
Primary Radar-Here the active cooperation of the target is required.
Secondary Radar-Hereactive cooperation of the target is not required. The transponder
plays an important role here.
Applications of radar:-
Itcan be used for air traffic control, aircraftnavigation, maritime navigation,
meteorological applications, spaceapplications, military applications and law
39. Page | 34
Radars usedin CNS:-
Range of radar depends on:-
Antenna gain, peak transmission power, atmospheric attenuation etc.
MAXIMUM RANGEOF A RADAR depends on:
• Peak transmission power (4th
• Minimum detectable signal(MDS)
• Antenna Gain
• Radar cross section of the target
• Atmospheric attenuation
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Monopulse Secondary Surveillance Radar (MSSR) is a radar systemthat can detect and measure the
position of aircraft i.e. distance and angle and requests for additional information from the aircraft itself
such as its identity and altitude.
MSSR technology is dependent upon the transponder. The radar sends an interrogating pulse and the
aircraft replies to each query by transmitting a response containing encoded data bits. Since the aircraft
sends a singlereplypulse, the technique is termed as Monopulse SSR technique. The Monopulse
technique makes the communication process
easier as it increases the azimuth accuracy. It
helps in calculating the azimuth angle of the
target w.r.t magnetic north.
The diagram shows a conventional main or "sum"
beam of an MSSR antenna to which a "difference"
beam has been added. The feed systemis divided
into two equal halves, the signal is distributed
horizontally across the antenna aperture and the
two parts are summed again to produce the
original sum beam. However the two halves are
also subtracted to produce a difference output. A signal arriving exactly normal, or at boresight, to the
antenna will produce a maximum output in the sum beam but a zero signal in the difference beam.
Away from boresight the signal in the sum beam will be less but there will be a non-zero signal in the
The angle of arrival of the signal can be determined by measuring the ratio of the signals between the
sum and difference beams.
There is one ENCODER present in the radar equipment box. It generates 16384 pulses in a 360ᴼ termed
as Azimuth Count Pulse (ACP). By counting the no. of pulses we can calculate the value of azimuthal
angle that the aircraft subtends with the magnetic North.
The formula can be given by Azimuthal Angle =
x (no.of ACPs at that point of time)
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The interrogator transmits a pair of pulses at 1030 MHz.
Each pulse has the same duration, shape and amplitude.
Their spacing distinguishes various modes of interrogation
P2 pulse use is for control
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SURFACE MOVEMENT RADAR
Used to detect aircraft and vehicles on the surface of an
Used by A Controllers to supplement visual observations.
Also used at night time and during low visibility to monitor the
movement of aircraft and vehicles
The Role of SMR
In the permanent absence of visual observation of all or part of the
manoeuvring area or to supplement (or in poor visibility, replace)
visual observation, SMR may be utilised to:
Monitor the movement of aircraft and vehicles on the
Provide routing information to pilots and vehicle drivers as necessary;
Provide advice and assistance for the safe and efficient movement of aircraft and vehicles on the
AIR TRAFFIC SERVICE (ATS)
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AUTOMATION SYSTEM – MISSION
To enhance the safety of the flights by providing the controllers with the information of air
– Surveillance Sensors such as Radars, ADS-B, Multilateration Systems and weather data
– Information such as Flight Plans, Route availability and Flow Management and communicate
control via Voice and Data Link.
The Kolkata ATM System is one of the most advanced safe and reliable ATM Data Processing and
Display systems available today. It boosts safety measures and efficiently manages the future air traffic
and reinforce Kolkata as an ATM reference for the whole Region.
MAIN CHARACTERISTICS OF AIRCON 2100
Open Architecture conforming to ISO/OSI.
Commercial Intel processors from HP for Servers and Workstations.
LINUX Red-Hat operating system.
High Resolution Displays:
• 2048x2048: SDD screen for Radar Controllers
• 1600x1280: FDD screen
• 1600x1280: SDD screens for Tower
Data Base for DBM: PostgreSQL
Use of high-level languages: ADA and C.
Use of standard graphics: X-Windows and Motif
The AirCon 2100 network is based in the Ethernet standards.
All servers and workstations have connection to the double Operational LAN
AIRCON ADVANCED FUNCTIONS
Multi-Sensor Surveillance Data Tracking and Fusion
Safety Nets (STCA, APW, MSAW)
4-D Trajectory Prediction
Medium Term Conflict Detection (MTCD)
System Availability & Recovery
Surveillance Bypass Facility
State-of-the-art ATM features incorporated in the system, those have already been implemented and
are in operational use, include but are not limited to:
– Advanced, user-friendly HMI specifically tailored for use by ACC/OCC, APP and TWR controllers,
and by Flight Data operators.
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– Enhanced multi-sensor surveillance tracking, including down-linked aircraft data, using Mode S
radars, ADS-B and Multilateration (MLAT/WAM) data, as well as primary and secondary radar
– Air-Ground Data Link applications (ADS-C, CPDLC, DCL) and services for aircraft-controller
– Advanced Flight Plan Processing and accurate 4-Dimensional Trajectory Calculation.
– Enhanced Safety Nets (STCA, MSAW, APW, APM, NTZ and others) and ATC Tools (Conformance
Monitoring and MTCD), including conflict prediction/detection alerts and warnings.
– Integrated Air Traffic Flow Control and Management (Flow prediction and Arrival Manager
Radar Data Compressor Unit – RDCU
Surveillance Data Processor – SDP
Flight Data Processor – FDP
Flight Data System – FDS
Data Link Server – DLS
Safety Nets (SFN)
Situation Data Display – SDD
Flight Data Display – FDD
System Monitoring and Control - SMC
Control and Monitoring Display – CMD
Data Analysis Tool – DAT
Arrival Manager – AMAN
Common Timing Facility – CTF
Data Recording Facilities – DRF
Data Base Manager – DBM
Graphic Tool Interface – GTI
Simulator System – SIM
Pilot Instructor Position – PILOT TSS
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Main System Components – Data Flow
Radar Data Compressor Unit
This processor centralizes the radar data reception from the radar. It can work in Main mode or
in Alternate mode (By-Pass) if other one fails. This component is designed in redundant configuration in
radar line reception, so as to easy to change the operative or reserve line manually or automatically.
Surveillance Data Processor -SDP
This component is in charge of handling of the primary, secondary and meteorological radar data
provided by the radars connected to the system. It processes the information and sends it to the SDDs
(Situation Data Displays) in order to show it on the controller screens. The SDP performs the following
1. Flight Plans and received radar information correlation.
2. Flight Plan Tracking
3. Flight Handover Management
4. Safety Alerts:
Minimum separation between aircrafts (Short Term Conflict Alert)
Minimum Safe Altitude warning.
Restricted Area warning
Clear Level Adherence Monitoring,
Route Adherence Monitoring.
5. ADS Tracking (if ADS is available)
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Kolkata ATM System Context
Flight Data Processor (FDP)
This component is in charge of Flights Plans management, generated or produced by external and
internal sources. The FDP performs the following tasks:
Repetitive Flight Plans (RPL) management.
Flight information inputs validation and check.
Coordination between adjacent control centres (AFTN, OLDI, and AIDC if applicable)
Reception and validation of the AFTN communications
Flight progression calculations.
Medium Term Conflict Detection (MTCD).
Flight plan information management and distribution.
Strip printing (if it is applicable for the system).
Restricted Areas Management.
Flight Data Service (FDS)
This function stores, collects and sends systemreal time data to external system(e.g. ASMGCS
and other ATC centres) and historic data to be used by internal data analysis tools (e.g. traffic statistics,
data test and verifying, events and log) and external tools (e.g. billing Airport FIDS).
Data Link Server (DLS)
The Air-Ground Data Link Processing (AGDLP) will be in charge of data link applications (ADS-C, CPDLC,
DCL) between aircraft and controllers and ensures the data communications with the air-ground
networks (ACARS) supplied by the service providers (e.g. SITA, ARINC).
The AGDLP is consists of following functions:
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o ATS Facilities Notification Manager: It allows addressing capability for data link applications
between aircraft and ground. The AFN application provides the capability to establish a logon
between ATS ground and aircraft systems and peer ATS ground systems. The status of aircraft
logged/de-logged is conveniently displayed to the controller.
o Automatic Dependent Surveillance – Contracts (ADS-C) Manager: It allows obtain positional and
other information from suitably equipped aircraft in a timely manner in accordance with the
established contracts between the Controller and the aircraft. The ADS-C Manager is responsible
to initiate, maintain, by events and cancel simultaneous contracts of type periodic, on demand,
by events or emergency. The periodical position report is used by the surveillance data
processing for the aircraft tracking in non-radar coverage areas.
o Controller Pilot Data Link Communication (CPDLC) Manager: It allows exchange data messages
between Controller and pilot. The CPDLC application provides the capability to established,
manage and terminate dialogues initiated by the pilot or by the Controller.
o Departure Clearance (DCL) Manager: It provides automated assistance for requesting and
delivering departure clearances through the data messages exchange between tower personnel
Safety Nets (SFN)
Safety nets alerts provided for:
o Short Term Conflict Alert (STCA) – detection and prediction of hazardous situations between
pair of tracks.
o Minimum Safe Altitude Warning – detection of track infringing, or predicted to infringe, terrain
or the minimum safe altitude above terrain defined for MSAW areas. It also detects track
predicted to deviate below the safe approach or departure path of defined aerodromes.
o Area Proximity Warning (APW) – detection of infringing tracks, or predicted to penetrate
restricted, prohibited or danger areas.
o Approaching Path Monitoring (APM) and Warning – monitoring and detection of track deviating
from the glide path and localizer at final approach.
o Distress, SPI and duplicated SSR Code Warning.
o RVSM alert.
o Specific ADS-C Alerts (RIE, NIC, ADS-C Emergency, FOM change).
o Mode-S alert.
Situation Data Display (SDD)
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It is based on powerful workstations where the data, radar data, and flight plans presentations
are carried out. These data are shown on the controller screens and it can show more information like
geographical maps, airways, meteorological data etc.
Flight Data Display (FDD)
This component present information about flight plans but it does not present any data about air
situations. It also allows the operators to manage the flight plans and other meaningful data like
activation of restricted areas, manage repetitive flight plans, AFTN correction messages, flow control,
Paged Information Pagination visualization, etc.
System, Monitoring and Control (SMC) / Control Monitoring Display (CMD)
It works as a component that supervises the whole system continuously and on real time. It also
allows the management of the components that fails or the ones that are not working correctly.
Data Analysis Tool (DAT)
This function encloses a set of functions for the analysis and study of the systemdata (e.g. traffic
statistics, data test and verifying, events and log) based on historic data provided by the Flight Data
Service (FDS) function.
It sequences the arrival flights for internal aerodromes, minimizing their arrival waiting times.
Common Timing Facility (CTF)
It manages the reception of the GPS time and delivers it via LAN to all the components and all the clocks
with NTP protocols.
Data Recording Facilities (DRF)
This component is based in the using of redundant RISC computers and records continuously all the data
related to the tracks data, flight plans data, and the controller actions to allow a playback reproduction
Data Base Manager (DBM)
It provides the systemwith the necessary data for the creation and modification of the database
adaptation data situating the systemin its geographical environment and upgrading the efficiency of the
MULTILATERATION SYSTEM (MLAT)
It is a navigation technique based on the measurement of the difference in distance to two stations at
known locations that broadcast signals at known times.
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Unlike measurements of absolute distance or angle, measuring the difference in distance between two
stations results in an infinite number of locations that satisfy the measurement. When these possible
locations are plotted, they form a hyperbolic curve. To locate the exact location along that curve,
multilateration relies on multiple measurements: a second measurement taken to a different pair of
stations will produce a second curve, which intersects with the first. When the two curves are
compared, a small number of possible locations are revealed, producing a "fix".
Multilateration is a common technique in radio navigation systems, where it is known as hyperbolic
navigation. These systems are relatively easy to construct as there is no need for a common clock, and
the difference in the signal timing can be measured visibly using an oscilloscope.
Multilateration should not be confused with trilateration, which uses distances or absolute
measurements of time-of-flight from three or more sites, or with triangulation, which uses the
measurement of absolute angles. Both of these systems are also commonly used with radio navigation
systems; trilateration is the basis of GPS.
CENTRALISED MAINTENANCE UNIT
CMU is a computerbasedsystemthatismeantfor communication(ground toground&ground to aircraft),
broadcastingmeteorological reportsandchecking the flight-planorroute of the aircraft inthe sky.
CMU meansCentralisedMaintenance Unit.Itconsistsof the followingparts:
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VHF RECEIVER TRANSMITTER SECTION:
VHF standsforVeryHighFrequencyradiorange.It isusedforground to aircraftcommunication.
For communicationpurpose the frequencyrange usedis 118 - 136.975 MHz
The channel separationused is25/ 8.33 KHz. Lesserthe channel separation;lesserwill be the
interference.The channel separationthusenhancesthe performance.
The VHF outputis maximum 50 Watts.
In Kolkata, there are 22 frequenciesinthe givenrange;outof which12 are used.
The emergencyfrequencyall overthe worldisprovidedas 121.5 MHz
VHF can covera range of 200 NM onlydue to earth curvature.Itis usedfor LOS.
In the CMU sectionthere isprovisionforusing24transmittersand48 receivers. The transmittersandreceivers
usedare all IPbased.Control personnelhaving the IPaddresscancontrol the aircraft fromanywhere of the
world.The receiversandtransmittersare connectedtoa24 port Ethernetswitch.
How the range of 200NM in VHFcommunicationcanbe increased?
In the earliersystem;supposeforaflightfromKolkatatoVaranasi;flight-plan;andall necessaryinformationwas
passedinthe following manner:VECC- VEGY; VEGY- VERP; VERP - VEPT;VEPT- VIBN. But nowadayswiththe
helpof MPLS (Multi-Protocol Label Switching) [provided byBSNLinKolkata] whichoperatesonTCPIPprotocol the
flight-plancanbe viewedfromanywhere.Thusthe disadvantage of VHF wasremoved.AlsobyusingRCAG
(Remote Control AirtoGround) we can achieve the desiredrange.
The MPLS line hasa B.W of 6 MBPS andthe E1 lines(there are 3 lines) have B.Wof 2 MBPS. The VHF transmitter
receiversystemoperatesondual LAN system.There isone mainsystemandthere isone standbysystemforback
up inemergencysituations.The transmittersare markedasT6T and receiversare markedasT6R. The 22
frequenciesare distributedamongdifferent sectionse.g.118.475 MHz is giventoTWR2; 119.3 MHz is givento
AppFNL. Greensymbol indicatesasecuredconnection;while redindicatesthatthe device hasnotbeeninstalled.
The emergencyfrequencyisgivento TX’s(TransmitterStandby).
The E1 linesare usedto connectthe followingairportswithKolkataairport - VOVZ(Vizag), VEBS(Bhubaneswar),
VARP(Raipur), VEJS(Jharsuguda), VEPT(Patna), VEBD(Bagdogra) andVEGT(Guwahati).
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DUAL LAN NETWORK
VCS WORKSTATIONS (TOUCH PANEL)
There isan analogand a digital recordertorecordall the voice communicationstakenplace.The analogtape
recorderconsistsof 128 channelswithone mainanda standbyunit.The digital recorderconsistsof 750 channels
dividedamongst3sets.The digital recorderisIPbasedand isconnectedviaRJ45 connector.
Recordedcontentsof analog recorder:
Statusof the siren(checkedat8:30 AM)
Recordedcontentsof digital recorder:
Statusof the siren(checkedat8:30 AM)
To keepweatherreports;there isone Digital AirportTerminal InformationSystem (DATIS).It operateson 126.4
MHz and usuallygivesthe meteorological reportsatan interval of 30 minutes.
Zenitel Transmitter employs web based control for operation. This handout is an introduction to web
In recent years, the Internet has proved a powerful tool for distributed collaborative work. The emerging
Internet technologies have the potential to apply the advantages of this way of working to the high-level
control of equipments. The advantages include:
52. Page | 47
Allowing remote monitoring and adjustment of equipments,
Allowing collaboration between skilled managers situated in geographically diverse locations
Allowing the business to relocate the physical location of equipment management staff easily in
response to business needs.
The design methodologies for the local computer-based control system are not appropriate for Internet-
based control system, as they do not consider the Internet environment issues such as Web-based
delay, Web-based safety, Web-based interface, and uncertain users.
A network is a system of hardware, software and transmission components that collectively allow two
application programs on two different stations connected to the network to communicate well. Figure 1
shows a typical Network
Fig: Typical Network
Networks are classified into several categories based on the application. Two important types of
Local Area Network
Wide Area Network
Local Area Networks (LAN)
LANs are limited to short geographical distances in the case of home, office, building, campus, industrial
park. Figure 2 shows a typical LAN
Fig: Typical Local Area Network
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Some features of LAN are:
Customer premises operation: User firm chooses technology, User firm needs to manage on
Low cost per bit transmitted: Companies can afford high speed, 100 Mbps to the desktop is
Wide Area Networks (WAN)
WANs are used to link sites at long distances. WAN requires the use of carriers to provide service. Figure
3 shows a typical WAN.
Fig: Typical Wide Area Network
WANs are normally interconnect several LANs. Some main features of WAN are:
Limited and complex choices.
High cost per bit transmitted.
Companies cannot afford high speeds. Usually low speed (56 kbps to a few megabits per
Network topology refers to the physical layout of the network. It refers to the physical location of the
computers and how the cables run between them. The four commonly used topologies are the Bus, the
Star, the Ring and the Mesh.
Network transmission media is the medium over which the information is exchanged between the
computers. Different mediums are used for this purpose namely Copper, Glass, Air, Radio etc. Each
media has certain characteristic features that make it suitable for particular networks. In Zenitel
network, Copper media in the form of Unshielded Twisted pair (UTP) cable is used for the LAN and Radio
in the form of UHF Link is used for the WAN.
Various special devices are used to interconnect components of a network. These devices are the Hub
(also called the Switch), the Router, the Bridge etc.
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The Switches allow simultaneous communication between two or more nodes, at a time. Switches are
used in single networks like LANs.
Multiple Networks are connected by Routers. An example of a Wide Area Network; the Internet is a
group of networks linked together with routers in a way that allows an application program on any
station on any network in the internet to be able to communicate with an application program on
another station on any other network.
Routers examine the network address field and determine the best route for a data packet. They have
the great advantage in that they normally support several different types of network layer protocols.
A protocol is a set of rules and formats that govern the communication between communicating devices
in a network. Protocols can be broadly divided into hardware and software categories.
Hardware protocols define the way the hardware device has to operate and work together. For example
10baseT Ethernet protocol is a hardware protocol specifying exactly the way the devices in a 10baseT
Ethernet network are physically connected, the voltage levels on the cables etc. There is no software
program involved, all is done with the hardware.
Programs in a network communicate with each other via software protocols. Network servers and
clients both have protocol packages that must be loaded to allow them to talk to each other.
Open System Interconnection (OSI) Model
The International Standard Organization (ISO) developed the OSI reference model 1n 1977. Since then
this has become the most widely accepted model for understanding network communication. The OSI
model is simply a conceptual framework made for better understanding of the complex interaction that
takes place among the various devices in the network. The OSI model consists of seven layers namely
Physical, Data Link, Network, Transport, Session, Presentation and Application layers as shown in fig.
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Each layer of OSI model has different protocols associated with it. When more than one protocol is
needed to complete a communication process, the protocols are grouped together in a stack. In fact
TCP/IP is a protocol stack.
The Physical layer is responsible for sending the bits from one machine to the other through the
transmission medium. Hubs, Repeaters, multiplexers etc. are all belong to physical layer in a network.
The main task of Data Link layer is to take the raw data and transform it into an organized data stream
that appears free of transmission errors to the network layer. In order to facilitate this the data link
layer adds control information to the data being sent. It also regulates the data flow rate.
The network layer is concerned with controlling the operation of the subnet. The data from the sender
may be required to travel through several links / subnets to reach the receiver. It is the task of the
network layer to make routing decisions and forward data packets. The Router is the network device
which operates in the network layer.
The basic function of the Transport layer is to accept data from session layer, split it up into smaller
units if needed and pass these to the network layer, and ensure that these pieces all arrive correctly at
the other end. The transport layer is a true end to end layer, from source to destination. In other words
a process on the sending machine carries on a direct conversation with the destination machine, using
the message headers and control information.
The Session layer allows applications on separate computers to share a connection called a Session. A
session allows ordinary data transport, as does the transport layer, but also provides enhanced services
useful in some applications. A session might be used to allow a user to log on to a remote timesharing
system or to transfer a file between two machines. Hence, one of the services of the Session layer is to
manage dialogue control
Presentation layer is concerned with the syntax and semantics of the information transmitted. This
layer translates data between the formats the network requires and the format the computer accepts.
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The major functions of this layer are protocol conversion, compression and encryption and
interpretation of graphic commands.
The Application layer is the topmost layer of the OSI model, and it provides services that directly
support user applications, such as database access, e-mail and file transfers. It also allows applications
to communicate with applications on other computers as though they were on the same computer.
The figure 5 explains communication process between two devices connected in an OSI model.
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TCP is a connection-oriented protocol that provides a virtual circuit between user application on sending
and receiving machines. TCP takes the data from the application layer protocols and breaks it into
segments and then makes sure that they reassembled at the receiving end.
IP takes the data from the host-to-host layer and fragments the information into packets. It labels each
packet of the sending device and the IP address of the receiving device. IP also reassembles packets on
the receiving machine into segments for upper layer protocols. IP is a connectionless protocol that has
no interest in the contents of the packets. It simply moves the packets to the destination.
The source and Destination machines in a TCP/IP environment are given a 32 bit address called the IP
Address. It consists of four 8 bit octets (each Octet is one byte). The IP address consists of network
identifier part and the host identifier. The address is coded to allow variable allocation of bits to specify
network and host. A typical IP address would be 184.108.40.206 (dotted decimal format). IP addresses
are hierarchical addresses in that they provide different levels of information. It can give the network
that the node resides on, the subnet it belongs to and the actual node address. This type of addressing
makes routing practical.
IP addresses have been broken down into three classes based on the size of network namely Class A,
Class B and Class C. Class A is used for very large networks and supplies over 16 million node addresses
for the network, Class B is used for networks containing a lot of nodes. Class C is used for small
58. Page | 53
NOTAM: Notice to Airmen originated by International NOTAM Offices (NOF) of each FIR to alert
aircraft pilots of potential hazards along a flight route or at a location that could affect the safety of the
A NOTAM shall be originated and issued promptly whenever the information to be distributed is of a
temporary nature and of short duration or when operationally significant permanent changes, or
temporary changes of long duration are made at short notice, except for extensive text and/or graphics.
NOTAMs are distributed by means of telecommunication (AFTN), that contain information concerning
the establishment, conditions or change in any aeronautical facility, service, procedure or hazard, the
timely knowledge of which is essential to personnel and systems concerned with flight operations.
The International NOTAM Office (NOF) Kolkata is responsible to process and originate NOTAMs of all
Airports & Airspace under Kolkata & Guwahati FIR and distribute all other NOFs and Airports through
AMSS/AFTN. Kolkata NOF also receives NOTAMs from other NOFs through AMSS/AFTN.
All these NOTAMs are stored in AMSS DATABASE Server for retrieval and generation of Preflight
Information Bulletin of NOTAMs for specific Aerodrome, FIR, Route for Pilots through ASBS
Terminals (Automatic Self Briefing System ) installed at Communication Briefing.
An example of NOTAM:
A) VECC B) 1601090905 C) 1601091500 EST
E) VHF 125.775MHZ VECC-VEBD SECTOR NOT AVBL)
Decoder of above NOTAM:
A0046/16 – Letter A indicate the Series, 0046/16 4-digit NOTAM number followed by a stroke and two
digits to indicate the year. [In India Series A for both International & National distribution, Series C for
National distribution and Series D for facilities of Defense Aerodrome with National distribution].
NOTAMN - Suffix N Indicates this is a new NOTAM. Other options are R for NOTAM replacing
another or C for one cancelling another.
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This is the "Q" or qualifier line, it always starts Q) and contains the following fields, each separated by a
FIR (here VECF , Kolkata FIR)
NOTAM Code, a 5 letter code starting with Q, defined in Annex 15. 2nd & 3rd letters CA indicates
Facility ,that it concerns about Air Ground facility. A full list of codes is included in ICAO document
8126 (Aeronautical Information Services Manual).
IV - Indicates that this is significant for IFR and VFR traffic
NBO - indicates for immediate attention of aircraft operators, for inclusion in PIB's and Operationally
significant for IFR flights
AE - Indicates scope, here A is Aerodrome, E is Enroute ( W for NAV warning)
000/999 - lower and upper limits expressed as a flight level. In this case it has been left as the default as it
is not applicable.
A) VECC - ICAO Location indicator of the Aerodrome where the facility is.
B) 1601050905 – Year 2016, Month 01 (January), Date 05, Time (HR&MIN) group (0905UTC) when
this NOTAM becomes effective.
C) 1601051500 EST - Date/time group (UTC) when the NOTAM ceases to be effective. Note "EST"
means "estimated". All NOTAM with EST remain in force until cancelled or replaced.
D) Time Schedule ( In this type NOTAM it is not required and not used)
E) VHF 125.775MHZ VECC-VEBD SECTOR NOT AVBL) - text of the NOTAM using ICAO
60. Page | 55
NAV-AIDS: Stands for navigationalaids. They are the tools which helps the aircraft in various
navigational functions such as aircraft take-off, landing and also helps it to maintain a correct bearing on
its route towards its destination.
NAV-AIDS are generally of four types:-
1) NDB (Non-directional beacon)
2) VOR (VHF Omni range)
3) DME (Distance measuring equipment)
4) ILS (Instrument landing system)
*NON-DIRECTIONAL BEACON (NDB): It helps the aircraft to determine its own position with respect to
the station/airport. It works on MF band. The range of frequencies allotted to it is 200 to 400 KHz. It
1) En-route aid
3) Position Fix
*VERY HIGH FREQUENCY OMNI RANGE (VOR): The main purpose of the VOR is to provide the
navigational signals for an aircraft receiver which will allow the pilot to determine the bearing of the
aircraft to a VOR facility. It also helps the aircraft in the scopes of the controller to be identified easily.
The VOR generally uses a frequency range between 108 to 118 MHz
The VOR’s are generally of two types:-
1) Terminal VOR-Not so commonly used
2) En-route VOR –This is the more frequently used and the maximum attainable frequency present in
this is 117.5 MHz
The models of VOR’s used in AAI are:-
1) Conventional VOR(CVOR)
2) Doppler VOR(DVOR)
Conventional VOR include the LORENZ, WILCOX models.
Doppler VOR’s include the models such as AWA,GCEL, and THALES-432 etc.
Nowadays THALES-432 is the most commonly used VOR.
Generally it has been found that the DVOR have better precision rates and are less error prone than the
CVOR’s. The DVOR uses the Doppler principle which states that an apparent frequency is generated
when there is relative movement between then source and the receiver.
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(Frequency range 190-535 KHz)
A non-directional (radio) beacon (NDB) is a radio transmitter at a known location, used as an aviation
or marine navigational aid. As the name implies, the signal transmitted does not include inherent
directional information, in contrast to other navigational aids such as low frequency radio range, VHF
omnidirectional range (VOR) and TACAN. NDB signals follow the curvature of the earth, so they can
be received at much greater distances at lower altitudes, a major advantage over VOR. However,
NDB signals are also affected more by atmospheric conditions, mountainous terrain, coastal
refraction and electrical storms, particularly at long range.
NDBs used for aviation are standardized by ICAO Annex 10 which specifies that NDBs be operated on
a frequency between 190 kHz and 1750 kHz, although normally all NDBs in North America operate
between 190 kHz and 535 kHz. Each NDB is identified by a one, two, or three-letter Morse code call
sign North American NDBs are categorized by power output, with low power rated at less than 50
watts, medium from 50 W to 2,000 W and high being over 2,000 W.
A bearing is a line passing through the station that points in a specific direction, such as 270 degrees
(due West). NDB bearings provide a charted, consistent method for defining paths aircraft can fly. In
this fashion, NDBs can, like VORs, define "airways" in the sky. Aircraft follow these pre-defined
routes to complete a flight plan. Airways are numbered and standardized on charts; coloured
airways are used for low to medium frequency stations like the NDB and are charted in brown on
sectional charts. Green and red airways are plotted east and west while amber and blue airways are
plotted north and south. While most airways in the United States are based on VORs, NDB airways
are common elsewhere, especially in the developing world like India and in lightly populated areas of
developed countries, like the Canadian Arctic, since they can have a long range and are much less
expensive to operate than VORs.
NDBs operate in Medium frequency range.
NDB provides magnetic bearing and DVOR provides relative bearing.
Bearing is always measured from Magnetic North.
True North is fixed and magnetic North varies, In India variation is about 2-6 degrees.
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(Frequency range 112-118 MHz)
VOR, short for VHF omnidirectional radio range, is a type of short-range radio navigation system for
aircraft,enablingaircrafttodetermine theirpositionandstayoncourse byreceivingradiosignalstransmitted
by a network of fixed ground radio beacons, with a receiver unit. It uses radio frequencies in the very high
frequency (VHF) band from 112 to 118 MHz
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DVOR or Doppler VOR is much more accurate than VOR as it reduces radial error to much more
extent. It works by radiating two low frequency signals:
Reference signal – maintains same phase throughout the azimuth- frequency fc
Variable signal – varies its phase according to the azimuth- frequency fc±9960
The phase angle comparison of both the reference and
variable signals gives the pilot the exact radial angle. North is
taken as reference, or it is assigned as 0°.
Fig: Showing central omnidirectional antenna and surrounding48 antennas.
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Purpose and use of ILS:
The Instrument Landing System (ILS) provides a means for safe landing of aircraft at airports under
conditions of low ceilings and limited visibility. The use of the system materially reduces interruptions of
service at airports resulting from bad weather by allowing operations to continue at lower weather
minimums. The ILS also increases the traffic handling capacity of the airport under all weather conditions.
The function of an ILS is to provide the PILOT or AUTOPILOT of a landing aircraft with the guidance to and along
the surface of the runway. This guidance must be of very high integrity to ensure that each landing has a very
high probability of success.
COMPONENTS OF ILS:
The basic philosophy of ILS is that ground installations, located in the vicinity of the runway, transmit
coded signals in such a manner that pilot is given information indicating position of the aircraft with
respect to correct approach path.
To provide correct approach path information to the pilot, three different signals are required to be
transmitted. The first signal gives the information to the pilot indicating the aircraft's position relative to
the center line of the runway. The second signal gives the information indicating the aircraft's position
relative to the required angle of descent, whereas the third signal provides distance information from
some specified point.
These three parameters which are essential for a safe landing are Azimuth Approach Guidance, Elevation
Approach Guidance and Range from the touch down point. These are provided to the pilot by the three
components of the ILS namely Localizer, Glide Path and Marker Beacons respectively. At some airports, the
Marker Beacons are replaced by a Distance Measuring Equipment (DME).
This information is summarized in the following table.
ILS Parameter ILS Component
a. Azimuth Approach Guidance Provided by Localizer
b. Elevation Approach Guidance Provided by Glide Path
c. Fixed Distances from Threshold Provided by Marker Beacons
d. Range from touch down point Provided by DME
Localizer unit: The localizer unit consists of an equipment building, the transmitter equipment, a
platform, the antennas, and field detectors. The antennas will be located about 1,000 feet from the
stop end of the runway and the building about 300 feet to the side. The detectors are mounted on
posts a short distance from the antennas.
Glide Path Unit:
The Glide Path unit is made up of a building, the transmitter equipment, the radiating a ntennas and
monitor antennas mounted on towers. The antennas and the building are located about 300 feet to
one side of the runway center line at a distance of approximately 1,000 feet from the approach end of
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Marker Units :
Three Marker Units are provided. Each marker unit consists of a building, transmitter and directional
antenna array. The system will be located near the runway centre line, extended. The transmitters are
75 MHz, low power units with keyed tone modulation. The units are controlled via lines from the
The outer marker
will be located
between 4 and 7
miles in front of the
approach end of the
runway, so the
pattern crosses the
glide angle at the
The modulation will
be 400 Hz keyed at 2
dashes per second.
The middle marker
will be located about
3500 feet from the
approach end of the
runway, so the
the glide angle at
200 feet. The
modulation will be a
1300 Hz tone keyed
by continuous dot,
Some ILS runways
have an inner
about 1.000 feet
from the approach
end of the runway,
so the pattern
intersects the glide
angle at 100 feet.
The transmitter is
modulated by a tone
of 3000 Hz keyed by
Distance Measuring Equipment (DME):
Where the provision of Marker Beacons is impracticable, a DME can be installed co-located with the Glide Path
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The ILS should be supplemented by sources of guidance information which will provide effective guidance to
the desired course. Locator Beacons, which are essentially low power NDBs, installed at Outer Marker and
Middle Marker locations will serve this purpose.
Aircraft ILS Component:
The Azimuth and Elevation guidance are provided by the Localizer and Glide Path respectively to the pilot
continuously by an on-board meter called the Cross Deviation Indicator (CDI).Range information is provided
continuouslyinthe form of digital readout if DME is used withILS. Howeverrange informationis not presented
continuously if Marker Beacons are used. In this condition aural and visual indications of specific distances
whenthe aircraft is overheadthe marker beaconsare providedby means of audio coded signals and lighting of
appropriate colored lamps in the cockpit.
FUNCTIONS OF ILS COMPONENTS:
A brief description of each of the ILS components is given in this section.
Function of Localizer unit :
The function of the Localizer unit is to provide, within its coverage limits, a vertical plane – o f c o u r s e
a l i g n e d with the extended center-line of the runway for azimuth guidance to landing aircraft. In addition,
it shall provide information to landing aircraft as to whether the aircraft is offset towards the left or right side
of this plane so as to enable the pilot to align with the course.
Function of Glide Path unit:
The function of the Glide Path unit is to provide, within its coverage limits, an inclined plane aligned with the
glide path of the runway for providing elevation guidance to landing aircraft. In addition, it shall provide
information to landing aircraft as to whether the aircraft is offset above or below this plane so as to enable the
pilot to align with the glide path.
Function of marker Beacon / DME:
The function of the marker beacons,/DME is to provide distance information from the touch down point to a
The marker beacons, installed at fixed distances from the runway threshold, provide specific distance
information whenever a landing aircraft is passing over any of these beacons so that the pilot can check his
altitude and correct it if necessary.
The DME, installedco-located with the Glide Path unit, will provide a continuous distance information from the
touch down point to landing aircraft.
Function of Locators:
The functionof locators,installed co-located with the marker beacons, is to guide aircraft coming for landing to
begin an ILS approach.
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CONTROL AND INDICATIONS IN AIRBORNE RECEIVER:
Block Diagram ILS Airborne Receiver
The salient features of the airborne display unit are as below:
a) There are two needles (vertical needle for localizer and the horizontal one for glide path).
b) There are twolines,vertical andhorizontal,crossingeachotheratthe centre of the meter and graduated
by a seriesof dots.There are four dotsabove andfour below the central dotonthe vertical line.Similarly
there are four dots left and four dots right of the central dot on the horizontal line.
c) The Localizer and Glide Path needles are driven by the DDMof respective radiation.
LOC GLIDE SLOPE INDICATOR AND RECEIVER
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I would like to say that this training program was an excellent opportunity for us to get to the ground
level and experience the things that we would have never gained through going straight into a job. I am
grateful to Airports Authority of India for giving us this wonderful opportunity.
The main objective of the industrial training is to provide an opportunity to undergraduates to identify,
observe and practice how engineering is applicable in the real industry. It is not only to get experience
on technical practices but also to observe live equipment and to interact with the staff of AAI. It is easy
to work with people, but not with sophisticated machines. The only chance that an undergraduate has
to have this experience is the industrial training period. I feel I got the maximum out of that experience.
Also I learnt the way of work in an organization, the importance of being punctual, the importance of
maximum commitment, and the importance of team spirit. The training included AMSS, VOLMET, ADS,
CPDLC, HFRECEIVER, ASMGCS, SMR, RADAR, DME and ILS. We learned not only through theory classes
but also through familiarisation of equipments.In my opinion, I have gained lot of knowledge and
experience needed to be successful in Aviation communication engineering.
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•Training material provided by the Airports Authority Of India