Report for Airports Authority of India for summer training program

1. ACKNOWLEDGEMENT
It was a great privilege for us to get our training at New ATS building, New Delhi under the
Airports Authority of India (AAI).
This report describes the training that we underwent, in the month of July 2013 under
Airport Authority of India (AAI). It was completed, keeping in mind the course curriculum as
per the university requirements.
We would like to express our sincere gratitude to all the people who have helped and
supported usthroughout. We are deeply indebted to Mr. RN GUPTA(Jt. Gen. Mgr.
(RTC)and Mr. S.K Tomar (Manager)and all other officials for organizing our training
programefficiently and providing us valuable resources and also for their cooperation and
willingness to share their expertise and knowledge and to devote their precious time to
discuss related topics. In the last but not the least our grateful appreciation is also extended
to our fellow batch mates for their support in developing this project.
The help and co-operation extended by the staff is fully acknowledged. We thoroughly
enjoyed our entire training program and would like to thank everyone at New ATS building,
IGI airport, New Delhi for their guidance and support.

2. 2
CONTENTS
TOPICS Page no.
Introduction to Airport Authority Of India 4
AIR TRAFFIC MANAGEMENT(ATM) 8
CNS
9
AIR TRAFFIC CONTROL (ATC)
>NAVIGATION
>SURVEILLANCE
>COMMUNICATION
11
12
13
14
ASMGCS UNIT
18
RADAR
30
TRANSMITTER
>HF TRANMITTER
>VHF TRANSMITTER
34
39
41
PROPAGATION
39
MODULATION
40
BIBLOGRAPHY
47

3. 3
Airport Authority of India
INTRODUCTION
Airport Authority of India (AAI) manages a total of 125 Airports, which include 11
International Airports, 08 Customs Airports, 81 Domestic Airports and 25 Civil Enclaves at
Defense Airfields. AAI also provides Air Traffic Management Services (ATMS) over entire
Indian Air Space and adjoining oceanic areas with ground installations at all Airports and 25
other locations to ensure safety of Aircraft operations. AAI provides air navigation services
over 2.8 million square nautical miles of air space.
The corporate headquarters (CHQ) are at Rajiv Gandhi Bhawan, Safdarjung Airport.
V.P Aggarwal is the current chairman of the AAI. Airports Authority of India has
responsibility of creating, upgrading, maintaining and managing civil aviation infrastructure
both on the ground and air space in the country.
All major air-routes over Indian landmass are Radar covered (29 Radar installations at 11
locations) along with VOR/DVOR coverage (89 installations) co-located with Distance
Measuring Equipment (90 installations). 52 runways are provided with ILS installations with
Night Landing Facilities at most of these Airports and Automatic Message Switching
System at 15 Airports.
AAI's successful implementation of Automatic Dependence Surveillance System (ADSS),
using indigenous technology, at Calcutta and Chennai Air Traffic Control Centers, gave
India the distinction of being the first country to use this advanced technology in the South
East Asian region thus enabling effective Air Traffic Control over oceanic areas using
satellite mode of communication. Use of remote controlled VHF coverage, along with
satellite communication links, has given added strength to our ATMS.

4. 4
AAI has also planned to provide Ground Based Augmentation System (GBAS) at Delhi and
Mumbai Airports. This GBAS equipment will be capable of providing Category-II (curved
approach) landing signals to the aircrafts thus replacing the existing instrument landing
system in the long run, which is required at each end of the runway.
The Advanced Surface Movement Guidance and Control System (ASMGCS), installed At
Delhi, have upgraded operation to runway 28 from CAT-IIIA level to CAT-IIIB level. CAT-
IIIA system permits landing of aircrafts up to visibility of 200mtrs. However, CAT-IIIB will
permit safe landing at the Airports at a visibility below 200mtrs but above 50mtrs.
AAI's Endeavour, in enhanced focus on 'customer's expectations', has evinced enthusiastic
response to independent agency, which has organized customer satisfaction surveys at 30
busy Airports. These surveys have enabled us to undertake improvements on aspects
recommended by the Airport users. The receptacles for our 'Business Reply Letters' at
Airports have gained popularity; these responses enable us to understand the changing
aspirations of Airport users. During the first year of the millennium, AAI endeavors to make
its operations more transparent and also make available the instantaneous information to
customers by deploying state-of-art Information Technology.
AAI has undertaken initiatives to upgrade training facilities at CATC Allahabad and
Hyderabad Airport. Aerodrome Visual Simulator (AVS) has been provided at CATC recently
and non-radar procedural ATC simulator equipment is being supplied to CATC Allahabad
and Hyderabad Airport.
HISTORY OF AAI
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.

5. 5
FUNCTIONS OF AAI
The functions of AAI are as follows:
1. Design, Development, Operation and Maintenance of international and domestic airports
and civil enclaves.
2. Control and Management of the Indian airspace extending beyond the territorial limits of
the country, as accepted by ICAO.
3. Construction, Modification and Management of passenger terminals.
4. Development and Management of cargo terminals at international and domestic airports.
5. Provision of passenger facilities and information system at the passenger terminals at
airports.
6. Expansion and strengthening of operation area, viz. Runways, Aprons, Taxiway etc.
7. Provision of visual aids.
Provision of Communication and Navigation aids, viz. ILS, DVOR, DME, Radar etc.
Security
The continuing security environment has brought into focus the need for strengthening security
of vital installations. There was thus an urgent need to revamp the security at airports not only
to thwart any misadventure but also to restore confidence of traveling public in the security of
air travel as a whole, which was shaken after 9/11 tragedy. With this in view, a number of steps
were taken including deployment of CISF for airport security, CCTV surveillance system at
sensitive airports, latest and state-of-the-art X-ray baggage inspection systems, premier
security & surveillance systems. Smart Cards for access control to vital installations at airports
are also being considered to supplement the efforts of security personnel at sensitive airports.

6. 6
AIRPORT CLASSIFICATION
Airports are presently classified in the following manner:
International Airports: - These are declared as international airports and are available for
scheduled international operations by Indian and foreign carriers. Presently, Mumbai, Delhi,
Chennai, Calcutta and Thiruvananthapuram are in this category.
Domestic Airports: - These are of two types: Custom & Model.
Custom Airports: -They are having limited international operations. These have customs
and immigration facilities for limited international operations by national carriers and for
foreign tourist and cargo charter flights. These include Bangalore (CE), Hyderabad,
Ahmadabad, Calicut, Goa (CE), Varanasi, Patna, Agra (CE), Jaipur, Amritsar, Tiruchirapally,
Coimbatore and Lucknow.(CE - Civil Enclave)
Model Airports: - These domestic airports have minimum runway length of 7500 feet and
adequate terminal capacity (400 passengers or more) to handle Airbus 320 type of aircraft.
These can cater to limited international traffic also, if required. These include Bhubaneswar,
Guwahati, Nagpur, Vadodara, Imphal and Indore. Rest 6 Nos. of airports, developed under
Model Airports concept has graduated to the classification of Customs Airports, given
above.
Other Domestic Airports: - All other 71 domestic airports are covered in this category.
Civil Enclaves in Defense Airport: - There are 28 civil enclaves in Defense airfields.
Twenty civil enclaves are in operation.

7. 7
AIR TRAFFIC MANAGEMENT (ATM)
An information service and alerting service are the basic levels of air traffic service, providing
information pertinent to the safe and efficient conduct of flights and alerting the relevant
authorities should an aircraft be in distress. These are available to all aircraft through an FIR.
FLIGHT INFORMATION REGION (FIR)
The airspace of the world has been divided into homogeneous regions called FIR’s. A Flight
Information Region (FIR) is an aviation term used to describe airspace with specific
dimensions, in which a Flight Information Service and an alerting service are provided. It is
the largest regular division of airspace in use in the world today.
Any portion of the atmosphere belongs to some specific FIR. Smaller countries' airspace is
encompassed by a single FIR, larger countries' airspace is subdivided into a number of
regional FIRs. Some FIRs may encompass the territorial airspace of several countries.
Oceanic airspace is divided into Oceanic Information Regions. The division among
authorities is done by international agreement through ICAO. There is no standard size for
FIRs.It is a matter for administrative convenience of the country concerned.
The FIR is responsible for providing air traffic services to all the flights that are: Entering
(overhead),Leaving (overhead), Taking off, And Landing.
In India,there are five such FIR’s namely:-Delhi, Mumbai, Chennai, Calcutta, &Guwahati.
The region of airspace over which an FIR is responsible for providing air traffic services is
broadly classified as Area, Approach, Tower
An FIR may include many airports within itself. For example the Delhi FIR includes Jaipur,
Varanasi, Nagpur, Amritsar airports etc. The Delhi airport is connected to all these stations
through various media links to enable the effective management of air traffic services in the
Delhi FIR

8. 8
CNS DEPARTMENT
Role of CNS department
To provide uninterrupted services of Communication, Navigation and Surveillance (CNS)
facilities for the smooth and safe movement of aircraft (over flying, departing & landing) in
accordance with ICAO standards and recommended practices.
 To maintain Security Equipment namely X-Ray Baggage systems (XBIS), Hand
Held Metal Detectors (HHMD) and Door Frame Metal Detectors (DFMD).
 To provide and maintain inter-unit communication facility i.e. Electronic Private
Automatic Exchange Board (EPABX)
 To maintain the Computer systems including peripherals like printers, UPS etc.
provided in various sections connected as standalone as well as on Local Area Network
(LAN).
 To maintain the passenger facilitation systems like Public Address (PA) system,
Car Hailing System and Flight Information Display System (FIDS).
 To maintain and operate Automatic Message Switching system (AMSS) used for
exchange of messages over Aeronautical Fixed Telecommunication Network (AFTN).
 To provide Communication Briefing to pilots by compiling NOTAM received from
other International NOF.
 To maintain and operate Fax machine.
 To co-ordinate with telephone service providers for provision and smooth
functioning of auto telephones/ hotlines/ data circuits.
COMMUNICATION SYSTEMS
Communication is the process of sending, receiving and processing of information by
electrical means. It started with wire telegraphy in 1840 followed by wire telephony and
subsequently by radio/wireless communication. The introduction of satellites and fiber
optics has made communication more widespread and effective with an increasing
emphasis on computer based digital data communication. In Radio communication, for

9. 9
transmission information/message 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 and radiated in the space, with the help of antenna. For reception
these electromagnetic waves received by the antenna, converted into electrical signals,
amplified, detected and reproduced in the original form of information/message with the
help of speaker.

10. 10
AIR TRAFFIC CONTROL (ATC)
Air traffic control (ATC) is a service provided by ground-based controllers who direct
aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to
separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to
provide information and other support for pilots when able.[1] In some countries, ATC may
also play a security or defense role (as in the United States), or be run entirely by the
military (as in Brazil).
Preventing collisions is referred to as separation, which is a term used to prevent aircraft
from coming too close to each other by use of lateral, vertical and longitudinal separation
minima; many aircraft now have collision avoidance systems installed to act as a backup to
ATC observation and instructions. In addition to its primary function, the ATC can provide
additional services such as providing information to pilots, weather and navigation
information and NOTAMs (NOtices To AirMen).
Figure: Voice Communication Control System
Depending on the type of flight and the class of airspace, ATC may issue instructions that
pilots are required to follow, or merely flight information to assist pilots operating in the

11. 11
airspace. In all cases, however, the pilot in command has final responsibility for the safety
of the flight, and may deviate from ATC instructions in an emergency.
NAVIGATIONAL AIDS
 NAVIGATION
Navigation is the process of reading, and controlling the movement of a craft or vehicle
from one place to another. It is also the term of art used for the specialized knowledge used
by navigators to perform navigation tasks. The word navigate is derived from the Latin
"navigate", which is the command "sail". Radio Navigation is based on the use of Radio
Transmitter, Radio Receiver and propagation of electromagnetic waves to find navigational
parameter such as direction, distance, position of the aircraft etc. According to service
range the radio navigational aids are broadly classified into three categories -
1. Long Range.
2. Medium Range.
3. Short range.
1. Long Range navigational aids
 Operate in very low frequency and low frequency, i.e. 10 KHz, 50-100 KHz and
100-200 KHz respectively.
 LORAN and OMEGA falls in this category.
2. Medium range navigational aids
 It operates in the LF or MF band of frequency.
 It gives the range of 150-250 nautical miles.
 NDB (Non Directional Beacons) falls in this category.
3. Short-range navigational aids

12. 12
 These aids operate in and above VHF bands.
 The coverage is dependent upon line of sight propagation.
 VHF, ILS, DME, VOR and RADAR are some widely used short-range aids
 Surveillance
While the evolving role of the Surveillance capability is less obvious than the PBN
‘revolution’ in Navigation and the system wide connectivity driving Communication
developments, Surveillance nevertheless continues to be an essential enabler to ATM
modernization.
Increasing traffic densities, pressures on the utilization of RF spectrum, new modes of
separation, including ASAS applications in the cockpit and improved safety nets are placing
greater demands on surveillance systems. These needs stimulate the use of new
surveillance techniques including ADS-B and Wide Area Multilateration which can deliver
improved performance in terms of accuracy, update rate, coverage and are also potentially
more efficient from an RF perspective than traditional SSR. Advanced multi-sensor
surveillance data fusion can also maximize the use of common airborne components,
depending on specific ground system requirements and the operational needs.
SESAR will develop an ADS-B ground-station to include the integration of WAM capability.
On the airborne side the ability of 1090MHz ADS-B to continue to work in the ever more
congested 1090MHz band is being investigated while the longer term view of a potential
new ADS-B system is also planned. Other options in the future could include satellite based
solutions and the evolution of the non-cooperative surveillance infrastructure.
The intelligent combination of these different surveillance techniques and the improved
sharing of surveillance data will allow a rationalization of the surveillance infrastructure
(especially in terms of multiple overlapping SSR as we have today) which should lower
costs and reduce the impact on the 1030/1090 spectrum extending its useful life as traffic
increases.ACAS evolution will also take account of new separation modes and the
coordination of airborne and ground-based safety nets also drives the development and
validation of the ground system capability to receive ACAS alerts to be made available to
the ground systems.

13. 13
INSTRUMENTATION LANDING SYSTEM (ILS)
An instrumentation landing system (ILS) is a ground-based instrument approach system
that provides precision guidance to an aircraft approaching and landing on a runway, using
a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a
safe landing during instrument meteorological conditions (IMC), such as low ceilings or
reduced visibility due to fog, rain, or blowing snow.
Instrument approach procedure charts (or approach plates) are published for each ILS
approach, providing pilots with the needed information to fly an ILS approach during
instrument flight rules (IFR) operations, including the radio frequencies used by the ILS
components or navaidsand the minimum visibility requirements prescribed for the specific
approach.
Radio-navigation aids must keep a certain degree of accuracy (set by international
standards of CAST/ICAO); to assure this is the case, flight inspection organizations
periodically check critical parameters with properly equipped aircraft to calibrate and certify
ILS precision.
TWO COMPONENTS OF ILS:
1. LOCALIZER
The localizer provides runway centerline guidance to aircraft. In some cases a localizer is
at an angle to the runway usually due to obstructions around the airport. It is then called a
Localizer Type Directional Aid. The Localizer is placed about 1,000 feet on the far end of
the approached runway. Its useful volume extends to 18 NM for the path up to 10 degrees
either side of the course. For an angle of 35 degrees either side of the course the useful
volume of the Localizer extends up to 10 NM. Localizer uses the frequency range 108-
112MHz. It’s frequency at Jaipur Airport is 109.9MHz.

14. 14
Figure: The Emission Patterns of the Localizer
2. GLIDE SLOPE
The function of the Glide Path(or glide slope) 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. The Glide Path gives the information indicating the aircraft’s position
relative to the required angle of descent. The MARRY antenna is used for it. Frequency
range for Glide path is 328-336MHz. It’s frequency at Jaipur Airport is 333.8MHz. Covering
range for Glide Path is 10NM. The Glide Path unit is made up of a building, the transmitter
equipment, the radiating antennas 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 about 1,000 feet from the approach end of the runway.
Figure: The Emission Patterns of theGlide Slope

15. 15
DME
Distance measuring equipment (DME) provides pilots with a slant range measurement of
distance to the runway in nautical miles. DMEs are augmenting or replacing markers in
many installations. The DME provides more accurate and continuous monitoring of correct
progress on the ILS glide slope to the pilot, and does not require an installation outside the
airport boundary.
Figure: DME435
When used in conjunction with an ILS, the DME is often sited midway between the
reciprocal runway thresholds with the internal delay modified so that one unit can provide
distance information to either runway threshold.

16. 16
Figure: Typical Locations of ILS Component

17. 17
ASMGCS
Introduction
The A-SMGCS system provides air traffic controllers with a complete picture of the airport
surface in all weather conditions. This improves the controller’s situational awareness
andincreases the level of safety at the airport.
A-SMGCS is used to:
– Reduce runway incursions
– Improve coordination between Air Traffic Control personnel
– Correlate flight plan information with aircraft position on control er displays
– Eliminate blind spots and coverage gaps
– Increase situational awareness in all weather conditions
– Support Airport Operations
• Snow removal coordination
• Departure and arrival queuing
• Taxi route monitoring
ASMGCS OVERVIEW
A-SMGCS combines multi-source surveillance data with target identification and Flight
Plan information into a “fused” system track. This system track is provided along with
safety logic alerts to improve the air traffic controller’s situation awareness

18. 18
A-SMGCS fuses five types of data; transponder multilateration (MLAT), surface
movementradar (SMR), Automatic Dependent Surveillance-Broadcast (ADS-B), Terminal
AirportRadar (TAR) and Flight Plan information.
The key sensors providing A-SMGCS target location data are the Radar Sensor and the
Multilateration Sensors
Figure: Showing the Position of Multilateration Sensor
Controller Display
The A-SMGCS Operational Display accurately presents a detailed picture of the Airport
Surface.
• Greater control of surface space in busy transportation centers.
• Controllers can accurately monitor aircraft movement in the approach and
departure corridors.
• Landing and taxing aircraft can be better controlled by maintaining safe distances
between all air traffic and service vehicles.
• Safety logic processing serves to provide controllers with visual and audible alerts
and warnings when safety conflicts occur.

19. 19
SystemCapabilities
A-SMGCS is designed to provide surveillance of the airport surface and approach
areas.
• In the movement area, the coverage is from the ground to a minimum of 300 feet
(91 m). The approach corridor is adaptable, but typically extends at least 5 nm
(nautical miles) beyond the runway threshold from the ground up to 5000 feet
(1524 m) or to match the glide slope. The approach corridors are covered in
configurable increments of 100 feet up to 5000 feet above ground level for every
one mile.
• Coverage is adaptable up to 50 nm range from the airport center and up to
100,000 feet (30,480 m) AMSL (above mean sea level).
• A-SMGCS provides accurate identification of al aircraft on the ground providing
the aircraft has an active transponder. The position and identification of each
tracked target (aircraft or vehicle) is updated once per second.
• A-SMGCS processes over 200 targets per second with a peak initiation rate of
20 new targets per second. The system tracks aircraft and vehicles entering the
coverage area within 5 seconds.
• A-SMGCS integrates Flight Plan information with position/identification
information. This combined system track is displayed on the controller display
within one second of an update.
• Less than one second processing delay
• ADS-B target reporting

20. 20
ASMGCS SYSTEM:
The A-SMGCS system is composed of many subsystems.
• The Surface Movement Radar (SMR) subsystem is a primary radar used
to detect surface targets, and report that information to other A-SMGCS
subsystems for processing. The SMR for your system is the Term
antenna and transceiver.
• The Multilateration subsystem (MLAT) is a secondary surveillance like
radar that provides position and identification of all transponder equipped
aircraft and vehicles.
• The Processor Subsystem combines (fuses) all sensor reports for a target,
determines target position, tracks the target, and provides safety logic
alerts.
• The Tower Display Subsystem provides the data and CWP displays for Air
Traffic Controller and Airway Facility Technician use.
• The Remote Monitoring System (RMS) provides the data and displays the
Airway Facility Technician uses to monitor, troubleshoot, and manage A-
SMGCS.
• The Communications subsystem provides data communications and
protocol conversion between various A-SMGCS subsystems and other
information sources such as ASR and Flight Plan systems.
Design Concept:
The A-SMGCS system was designed to be flexible and adaptable to meet the
coverage requirements unique to each airport.
• The A-SMGCS configuration allows different architectures to be deployed
without any special software. For example, remote units can be configured
from as few as 4 up to a maximum of 32.
• A LAN architecture connects the A-SMGCS subsystems. The use of a LAN
architecture allows A-SMGCS to interface with other Air Traffic systems
and supports multiple display processors, which in turn support, multiple
operator displays.

21. 21
• The CPU processor capability al ows for future growth for increased target
processing, to provide future safety logic enhancements, to support
multiple and/or remote SMR configurations.
• Modular construction supports primary and secondary equipment
redundancy for critical components, removal and replacement of Line
Replaceable Units (LRUs), and a low mean time to repair
PROCESSING OVERVIEW
The A-SMGCS system performs target detection and tracks targets of interest on the
airport surface and in the approach corridors. The system accomplishes this using
multiple sensors and a fusion processor.
The primary A-SMGCS sensors are the Multilateration (MLAT) and Surface Movement
Radar (SMR) subsystems. These sensors contain processors that perform target
detection and tracking.
 The Radar Data Processor (RDPi) performs target detection and tracking on raw
video received by the SMR transceiver. The RDP sends target and plot data to the
Single Sensor Data Processor (SSDP).
 The Target Processor (TP) performs target detection, identification, and tracking based on
ATCRBS, Mode S, and ADS-B replies received by the MLAT Remote Units(RUs).
 The RDPi and TP maintain their own local track databases, but they also share their
local track information with the A-SMGCS fusion processor. In an A-SMGCS system,
the fusion processor is the Multi-Sensor Data Processor (MSDP). The MSDP’s Multi-
Sensor Track Maintenance (MSTM) process handles fusion processing.
 The Terminal Airport Radar (TAR) input provides coverage off of the airport surface
(adaptable out to 250 nm). In addition, it provides a seamless transition for targets
transitioning between the airport surface and the approach corridors.
 External MLAT: For systems with an external MLAT tracker, the ASDP receives the
target tracks, performs association logic for existing tracks and sends track reports to
the MSTM.
 The Flight Plan interface (FLIP) allows the MSTM to include flight plan information for
any targets that have Mode 3/A identification (MLAT or TAR only).
 The MSTM process fuses all of these sensor inputs into a single system track output to

22. 22
the Display Processor (DP)
A-SMGCS SUBSYSTEM
The purpose and major components of each A-SMGCS subsystem:
 Multilateration Subsystem
 Surface Movement Radar (SMR) Subsystem
 Processing Subsystems (Processor, RMS, and Display)
 Communications Subsystem
 Subsystem Interrelationship

23. 23
1.Multilateration System
The Multilateration (MLAT) Subsystem is a secondary surveillance sensor that provides
accurate position and identification information on transponder equipped aircraft and
surface vehicles.
The multilateration subsystem contains the following major components
 Remote Units (RUs)
 Reference Transmitters (RefTrans)
 Target Processors (TPs)
i) Remote Unit (RU)
Remote units are the sensors used by A-SMGCS to detect transponder signals. These
signals (ATCRBS & MODE S)are time stamped and passed to the target processor for
multilateration.
There are two types of RUs:
 Receive Only (RO)
 Receive/Transmit (R/T).
The RO and R/T are based on a common architecture.The RU elements are
configurable by software and hardware to operate as eitheran RO unit or an R/T. To
operate as an R/T, the unit requires the addition of a transmitter module.
Figure: Remote Unit

24. 24
ii) Reference Transmitter (RefTrans):
 RefTrans are used to calibrate the target processor’s Time Difference of Arrival
Function (TDOA).
RefTrans perform this function by squitting Mode-S messages. These squitters are from a
known location and the multilated position provides calibration. The RUs detect the
RefTran squit as a Mode S message – it will be time stamped and provided to the TP.
The TP uses these squits for RU Time Correction
 Calibration is necessary for accurate multilateration.
– For redundancy, each RefTran has two transmitters.
 The number and placement of RUs and RefTrans is determined through site
surveys and mathematical modeling of the coverage area.
Figure:Reference Transmitter (Reftran)

25. 25
iii) Target Processor:
Target Processor is located in the Processor Cabinet; it is part of the multilateration
subsystem. The TP is the processor that performs Time Difference of Arrival
(TDOA) processing, better known as multilateration.
The TP will perform TDOA processing on signals received at the Remote Units. The
types of signals it will process include:
• ATCRBS replies
• Mode-S replies
• Mode-S squitters
• RefTran Mode-S squitters
The TP processes targets (received by the RUs) as track and identification data.
The track information will be passed to the MSDP for fusion processing.
There is one primary and one secondary TP. In the event the primary fails, there is
an automatic switchover to the secondary TP.
Target Position Estimator (TAPER):
TAPER receives target detections from RUCIS and performs RU clustering, time RUC
and performs RU clustering, time correction, and target position Positions are forwarded
to the ASTP. If the detection is a RefTran detection, a copy of the cluster is sent on to
REFSYNC. RU2RU3
RefTran Synchronization (REFSYNC): REFSYNC uses the precisely known positions of
the RU and RefTran antennas and the RU timestamps of RefTran detections to create a
table of offsets & drifts used to correlate the free-running RU clocks. REFSYNC provides
time tracking information that TAPER uses to correct the RU Timestamps
Airport Surveillance Track Processor (ASTP): ASTP provides target tracking for each
detected target. ASTP associates incoming targets, models the motion of each target,
predicts its next position, validates the positions provided by TAPER, and issues target
interrogation requests to RUCIS. Target positions in Sensis Generic Format (SGF) are
provided to the fusion processor.

26. 26
2.SMR SUBSYSTEM
Surface Movement Radar (SMR): The SMR is a primary radar. It provides target
detection and tracking for targets on the airport surface. The SMR is comprised of two
main subsystems:
Transceiver: the transceiver creates radio frequency (RF) pulses for transmission,
down-converts RF echoes to video, converts the video from analog to digital, and
performs 4-Pulse Non-Coherent Integration (NCI) processing on the video. Digital
targets are provided to the RDPi in a Batch PRI Range Cell (BPRC) format.
Radar Data Processor-Improved (RDPi): The Sensis RDPi receives digital video in
BPRC format from the transceiver. It performs target detection and target tracking with
Signal and Data Processor functions:
 The Signal Processor performs target detection. It receives the 8-bit video from the
transceiver, computes adaptive thresholds, performs threshold tests, and generates
radar plots for use by the data processor. It provides the data processor with two types
of plots:
– Target plots used for target detection and
– Static reflector plots used in multipath processing
 The Data Processor performs target tracking. It processes target plots (primitives) on
a scan by scan basis. Then, it either associates and updates established tracks or
initiates tracks. In addition, it compares static reflector plots and established tracks with
new tracks to determine if the new track is the result of multipath. The data processor
outputs track information in a Cat10 format to an SSDP in the MSDP
Terminal Radar Plots:
The Terminal Area Radar (TAR) is the long range (approach) sensor in an A-SMGCS
system used to monitor targets in the approach corridors. It is external to the A-SMGCS
system, with data typical y fed to the system through a serial link. The TAR may be a
primary surveillance radar (PSR) only or may include a secondary surveillance radar
(SSR). A-SMGCS expects to receive the following target information from the TAR
interface

27. 27
 PSR:
 Range
 Azimuth
 SSR:
 Mode A reply
 Mode C reply
Since the data for this sensor is provided by the customer, Terminal Radar data must be
aligned with MLAT data for proper coverage. This alignment is performed after MLAT
alignment is complete.
3.FUSION PROCESSOR (MSDP)
Multi Sensor Data Processor
The purpose of the Multi-Sensor Data Processor (MSDP) is to process all surveillance
and target information sources and provide an integrated (fused) output to the Display
subsystem. The MSDP is the heart of the A-SMGCS system.
Functions
It processes data from all connected subsystems:
 SMR plot and track data based on radar measured position.
 Multilateration plot and track data (including identification) based on multilaterated
position measurements from beacon-equipped targets.
 GPS-based position measurements from ADS-B equipped targets.
 Terminal radar plots.
 Flight Plan information.(Note: If both MSDPs are reset, it may take up to one hour before
information is available from FPDS for departing aircraft.)
 Subsystem Status messages from each connected subsystem.
 Safety Logic audible and visual alerts.
Display Subsystem
The Display Subsystem provides the interface used by operators to view and manage A-
SMGCS target and map information:
The Display Subsystem contains:
 Up to 15 KVM Extenders (Receiver/Transmitter pairs)

28. 28
 Up to 15 Display Processors (DPs)
 Display Processors #3 thru #17 are in the Display Processor Cabinet(s)
 One Tower Display (CWP) (with safety logic speaker) per DP
 Two Ethernet Switches per rack
The purpose of the display processor is to convert the MSDP map and target data into a
visual representation of the airport surface and targets in the coverage volume.
Functions
 The display processor receives map, track, data tags, and system status information
from the MSDP in the form of broadcast messages. It converts these messages into
video for display to the operators.
 It saves, updates, and recall user preferences to/from the MSDP and sends control
messages to the MSDP.
 It uses blocking read functions so that the Display Processor can update the display
viewed by an operator in response to an operator changing Map Range and read
MSDP messages simultaneously.
 It accepts operator input via the input devices and responds accordingly,
 Such as repositioning a map, creating and saving user preference sets, etc.
4.RMS Subsystem
Remote Monitoring Subsystem (RMS):
The RMS is to the primary subsystem used to monitor, troubleshoot and manage the A-
SMGCS system
The RMS Subsystem contains the following components:
1. Maintenance Display Terminal (MDT)
2. Data Recording Facility (DRF)
3. Two DPs
4. KVM Switch
5. One Display
6. Storage Server

29. 29
RADAR
(Frequency range: MSSR L band (1030 MHz and 1090 MHz) ASR S band (2.7- 2.9 MHz)
Radar is an object-detection system which uses radio waves to determine the range,
altitude, direction or speed of objects. Radar stands for RAdio Detection And Ranging.
It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles,
weather formations, and terrain. The radar dish or antenna transmits pulses of radio
waves or microwaves which bounce off any object in their path. The object returns a
tiny part of the wave's energy to a dish or antenna which is usually located at the same
site as the transmitter.
Classification:-
Based on operation:
Primary Radar Co-operation of targets is not required for detection. It works
on ―echo‖ technology.
Secondary Radar Active co-operation of targets is required for finding range and other
details of target.
Based on waveform:
CW Radar- can detect moving target and its velocity.
CWFM Radar – can detect range using fm signals.
Pulsed Radar -uses pulse modulated microwave signals for detecting range & velocity.

30. 30
Based on services:
Search Radar also known as surveillance radar. Uses continuously rotating antenna.
Covers large volume of space.
Tracking Radar gives accurate angular position, range and radial velocity of targets
with precision. If used for tracking it must first be co-located with search radar for
1st acquiring the target.
Applications
o Air Traffic Control
o Aircraft Navigation
o Maritime Navigation
o Meteorological Applications
o Space Applications
o Military Applications
o Law Enforcement Applications

31. 31
Radars used in ATC
 Airport Surveillance Radar (ASR)
 Air Route Surveillance Radar (SSR)
 Airport Surface Movement Detection Equipment (ASDE)
 Precision Approach Radar (PAR)
 Monopulse Secondary Surveillance Radar (MSSR)
 Maximum range of RADAR depends on:-
(1) Peak transmission power (4th root)
(2) Minimum detectable signal (MDS)
(3) Antenna Gain
(4) Radar Cross Section of the target
(5) Atmospheric Attenuation
Primary Radar
Primary Radar works on the principle of reflection or ―echo‖. Primary radar antennae
continuously send pulses in all possible directions. When these pulses hit some moving or
still objects, the pulse is reflected back to the antenna. Generally the radar transmitter and
receiver are located at the same located. The radar processes the information and
confirms the presence of an object. If the object is moving either closer or farther away,
there is a slight change in the frequency of the radio waves, caused by the Doppler effect.

32. 32
Secondary Radar
Secondary radar works target specific. An interrogation pulse is sent from the radar
transmitter. The target, on receiving the signal, replies back with another signal. The radar
then processes the distance covered by the signal and the time taken for the operation
and calculates the position of the target accordingly. One kind of secondary radar used by
ATC is MSSR or Monopulse Secondary Surveillance Radar.
MSSR Interrogation
 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 is used for control.
Transponder Reply
 F1 and F2 are always present (―framing pulses‖).
 The 12 binary data pulses in four groups of 3 bits: A,B,C,D.
 4096 possible ID codes (Mode 3/A reply).
 Special codes: 7500=Hijack, 7600=Comm Fail, 7700=Emergency.
 2048 permutations (D1 omitted) of altitude code (Mode C reply) indicating heights.
 SPI (Special Position Indicator) pulse is used upon request by ground control.

33. 33
TRANSMITTERS
AM Transmitters
Transmitters that transmit AM signals are known as AM transmitters. These transmitters
are used in medium wave (MW) and short wave (SW) frequency bands for AM broadcast.
The MW band has frequencies between 550 KHz and 1650 KHz, and the SW band has
frequencies ranging from 3 MHz to 30 MHz. The two types of AM transmitters that are
used based on their transmitting powers are:
 High Level
 Low Level
High level transmitters use high level modulation, and low level transmitters use low level
modulation. The choice between the two modulation schemes depends on the transmitting
power of the AM transmitter. In broadcast transmitters, where the transmitting power may
be of the order of kilowatts, high level modulation is employed. In low power transmitters,
where only a few watts of transmitting power are required , low level modulation is used.
High-Level and Low-Level Transmitters
Below figure shows the block diagram of high-level and low-level transmitters. The basic
difference between the two transmitters is the power amplification of the carrier and
modulating signals.
Figure (a) is drawn for audio transmission. In high-level transmission, the powers of the
carrier and modulating signals are amplified before applying them to the modulator stage,
as shown in figure (a). In low-level modulation, the powers of the two input signals of the
modulator stage are not amplified. The required transmitting power is obtained from the
last stage of the transmitter, the class C power amplifier.

34. 34
The various sections of the figure (a) are:
 Carrier oscillator
 Buffer amplifier
 Frequency multiplier
 Power amplifier
 Audio chain
 Modulated class C power amplifier
Carrier oscillator
The carrier oscillator generates the carrier signal, which lies in the RF range. The
frequency of the carrier is always very high. Because it is very difficult to generate high
frequencies with good frequency stability, the carrier oscillator generates a sub multiple
with the required carrier frequency. This sub multiple frequency is multiplied by the
frequency multiplier stage to get the required carrier frequency. Further, a crystal oscillator
can be used in this stage to generate a low frequency carrier with the best frequency
stability. The frequency multiplier stage then increases the frequency of the carrier to its
required value.

35. 35
Buffer Amplifier
The purpose of the buffer amplifier is two fold. It first matches the output impedance of the
carrier oscillator with the input impedance of the frequency multiplier, the next stage of the
carrier oscillator. It then isolates the carrier oscillator and frequency multiplier.
This is required so that the multiplier does not draw a large current from the carrier
oscillator. If this occurs, the frequency of the carrier oscillator will not remain stable.
Frequency Multiplier
The sub-multiple frequency of the carrier signal, generated by the carrier oscillator , is now
applied to the frequency multiplier through the buffer amplifier. This stage is also known as
harmonic generator. The frequency multiplier generates higher harmonics of carrier
oscillator frequency. The frequency multiplier is a tuned circuit that can be tuned to the
requisite carrier frequency that is to be transmitted.
Power Amplifier
The power of the carrier signal is then amplified in the power amplifier stage. This is the
basic requirement of a high-level transmitter. A class C power amplifier gives high power
current pulses of the carrier signal at its output.
Audio Chain
The audio signal to be transmitted is obtained from the microphone, as shown in figure
(a). The audio driver amplifier amplifies the voltage of this signal. This amplification is
necessary to drive the audio power amplifier. Next, a class A or a class B power amplifier
amplifies the power of the audio signal.
Modulated Class C Amplifier
This is the output stage of the transmitter. The modulating audio signal and the carrier
signal, after power amplification, are applied to this modulating stage. The modulation
takes place at this stage. The class C amplifier also amplifies the power of the AM signal
to the reacquired transmitting power. This signal is finally passed to the antenna., which
radiates the signal into space of transmission.

36. 36
.
The low-level AM transmitter shown in the figure (b) is similar to a high-level transmitter,
except that the powers of the carrier and audio signals are not amplified. These two
signals are directly applied to the modulated class C power amplifier.
Modulation takes place at the stage, and the power of the modulated signal is amplified to
the required transmitting power level. The transmitting antenna then transmits the signal.
Coupling of Output Stage and Antenna
The output stage of the modulated class C power amplifier feeds the signal to the
transmitting antenna. To transfer maximum power from the output stage to the antenna it
is necessary that the impedance of the two sections match. For this , a matching network
is required. The matching between the two should be perfect at all transmitting
frequencies. As the matching is required at different frequencies, inductors and capacitors
offering different impedance at different frequencies are used in the matching networks.
The matching network must be constructed using these passive components. This is
shown in Figure (c).

37. 37
The matching network used for coupling the output stage of the transmitter and the
antenna is called double π-network. This network is shown in figure (c). It consists of two
inductors , L1 and L2 and two capacitors, C1 and C2. The values of these components are
chosen such that the input impedance of the network between 1 and 1'. Shown in figure
(c) is matched with the output impedance of the output stage of the transmitter. Further,
the output impedance of the network is matched with the impedance of the antenna.
The double π matching network also filters unwanted frequency components appearing at
the output of the last stage of the transmitter. The output of the modulated class C power
amplifier may contain higher harmonics, such as second and third harmonics, that are
highly undesirable. The frequency response of the matching network is set such that these
unwanted higher harmonics are totally suppressed, and only the desired signal is coupled
to the antenna.
HF COMMUNICATION
HFs (2–30 MHz) offer long-range and even worldwide communication via the ionosphere.
Since HF systems require only modest transmitters and antennas, and do not require
external infrastructure, HF links can be easily established from remote locations, or
following a natural disaster. Terminals are often connected to the local PSTN or Internet to
allow remote access. HF is widely used for voice and data communication by military,
diplomatic, aeronautical, marine, and amateur-radio services. However, the variable and
dispersive nature of the ionosphere imposes some unique requirements on both hardware
and communication protocols.

38. 38
HF Communication Systems
The transmitting station consists of a transmitter, matching network, and antenna. The
receiving station includes an antenna, matching network or active preamplifier, and
receiver. Most HF equipment is operable over all or most of the 2–30-MHz range, and
each group of users is typically assigned a number of frequencies or bands. HF systems
employ a wide variety of transmitting antennas [1]. Low-angle radiation is needed for long-
range communication, while high-angle radiation is needed for shorter range “near-
vertical-incidence-skywave (NVIS) communication. It is not necessary to match the
polarizations of the transmitting and receiving antennas because the ionosphere generally
produces elliptical polarization.
Low-angle directional transmission is usually accomplished by a mechanically rotated
“beam” such as a Yagi (specific frequency) or log-periodic dipole array (band of
frequencies). The gains are typically in the range of 3–10 dB. Low-angle omnidirectional
transmissions typically use monopoles.
PROPAGATION

39. 39
The ionosphere is created by ionization of the upper atmosphere by ultraviolet and X-rays,
and is divided into , and layers. The layer extends from 150 to 650 km and is responsible
for most long-range HF propagation. Since theionization varies with altitude, signals are
not reflected, but refracted by the ionosphere. Signals of different frequencies are thus
returned to Earth at different distances (or not at all), . During the daytime, the “skip
distance” for a 7-MHz signal might be 300 km, while that of 21-MHz signal could be 3000
km.With the lower electron densities at night, the skip at 7 MHz might increase to 2000
km, while 21 MHz would not be returned at all. Long-range communication can also be
accomplished over multiple-hop paths that include a reflection from the earth or layer.
Conditions vary with the time of day, latitude, season, and solar conditions. Predictions
are made by a variety of programs including IONCAP, PROPMAN, and MINIMUF
MODULATION
Early HF communication used CW (Morse) and some full carrier AM signals. In the late
1950s, SSB became dominant for voice communication and FSK was used for radio
teletype. While SSB continues to be used, much of the traffic is no win the form of digital
voice and packetized data. Modern digital techniques are based upon PSK and offer
data rates up to 14.4 kb/s Speech is encoded by the LPC-10 technique. LPC-10 is based
upon linear-predictive coding with ten poles (five resonances) Basically, in each 22.5-ms
time frame, the vocoder fits the five resonances to the speech waveform. The resonance
information requires a data rate of 1200–2400 b/s. The receiver synthesizes the speech
waveform from the resonance data

40. 40
TYPICAL EQUIPMENT
The AN/VRC-100 transceiver (Fig. 2) illustrates the state-of-the-art in ground/vehicular
HF-communications trans- receivers. It operates from 2 to 30 MHz, produces power
outputs to 175-W PEP, and supports a wide variety of modulationtypes including
USB/LSB, AME, CW, and various ECCM waveforms. The AN/VRC-100 provides ALE in
accordance with MIL-STD-188-141A, as well as the alternative quick call (AQC) ALE,
which has the potential to reduce the call time by as much as 50%. The system consists of
three line replaceable units (LRUs), i.e., receiver/transmitter, the power amplifier/coupler,
and the control/display unit. Tuning time into a new load is nominally 1 s, but is reduced to
35 ms for power tuned frequency
Vhf transmitter
Very high frequency (VHF) is the ITU-designated range [1] of radio
frequencyelectromagnetic waves from 30 MHz to 300 MHz. Frequencies immediately
below VHF are denoted high frequency (HF), and the next higher frequencies are known
as ultra high frequency (UHF).
These names referring to frequency usage originate from the early 20th century, when
regular radio service used the terms LF (low frequencies), MF (medium frequencies), and
HF (high frequencies). These names were standardized by the International
Telecommunications Union (ITU) and extended to higher frequency ranges.

41. 41
Common uses for VHF are FM radio broadcasting, television broadcasting, land mobile
stations (emergency, business, private use and military), long range data communication
up to several tens of kilometres with radio modems, amateur radio and marine
communications. Air traffic control communications and air navigation systems (e.g. VOR,
DME&ILS) work at distances of 100 kilometres or more to aircraft at cruising altitude
Line-of-sight calculation
For analog TV, VHF transmission range is a function of transmitter power, receiver
sensitivity, and distance to the horizon, since VHF signals propagate under normal
conditions as a near line-of-sight phenomenon. The distance to the radio horizon is slightly
extended over the geometric line of sight to the horizon, as radio waves are weakly bent
back toward the Earth by the atmosphere.
An approximation to calculate the line-of-sight horizon distance (on Earth) is:
 distance in nautical miles = where is the height of the antenna in
feet
 distance in kilometres = where is the height of the antenna
in metres.
These approximations are only valid for antennas at heights that are small compared to
the radius of the Earth. They may not necessarily be accurate in mountainous areas, since
the landscape may not be transparent enough for radio waves.
In engineered communications systems, more complex calculations are required to assess the
probable coverage area of a proposed transmitter station.
The accuracy of these calculations for digital TV signals is being debated

42. 42
VHF OMNI DIRECTIONAL RANGE
VHF omni directional radio range (VOR), is a type of short-range radio navigation
system for aircraft, enabling aircraft to determine their position and stay on course by
receiving radio signals transmitted by a network of fixed ground radio beacons, with a
receiver unit. It uses radio frequencies in the very high frequency (VHF) band from 108 to
117.95 MHz. Developed in the US beginning in 1937 and deployed by 1946, VOR is the
standard air navigational system in the world, used by both commercial and general
aviation. There are about 3000 VOR stations around the world.
A VORs ground station sends out a master signal, and a highly directional second signal
that varies in phase 30 times a second compared to the master. This signal is timed so
that the phase varies as the secondary antenna spins, such that when the antenna is 90
degrees from north, the signal is 90 degrees out of phase of the master. By comparing the
phase of the secondary signal to the master, the angle (bearing) to the station can be
determined. This bearing is then displayed in the cockpit of the aircraft, and can be used
to take a fix as in earlier radio direction finding (RDF) systems, although it is, in theory,
easier to use and more accurate. This line of position is called the "radial" from the VOR.
The intersection of two radials from different VOR stations on a chart provides the position
of the aircraft. VOR stations are fairly short range: the signals have a range of about 200
miles.

43. 43
Operation
VORs are assigned radio channels between 108.0 MHz and 117.95 MHz (with 50 kHz
spacing); this is in the Very High Frequency (VHF) range. The first 4 MHz is shared with
the Instrument landing system (ILS) band. To leave channels for ILS, in the range 108.0 to
111.95 MHz, the 100 kHz digit is always even, so 108.00, 108.05, 108.20, 108.25, and so
on are VOR frequencies but 108.10, 108.15, 108.30, 108.35 and so on, are reserved for
ILS
The VOR encodes azimuth (direction from the station) as the phase relationship of a
reference and a variable signal. The omni-directional signal contains a modulated
continuous wave (MCW) 7 wpm Morse code station identifier, and usually contains an
amplitude modulated (AM) voice channel. The conventional 30 Hz reference signal is on a
9960 Hz frequency modulated (FM) subcarrier. The variable amplitude modulated (AM)
signal is conventionally derived from the lighthouse-like rotation of a directional antenna
array 30 times per second. Although older antennas were mechanically rotated, current
installations scan electronically to achieve an equivalent result with no moving parts.
When the signal is received in the aircraft, the two 30 Hz signals are detected and then
compared to determine the phase angle between them. The phase angle by which the AM
signal lags the FM subcarrier signal is equal to the direction from the station to the aircraft,
in degrees from local magnetic north at the time of installation, and is called the radial.
The Magnetic Variation changes over time so the radial may be a few degrees off from the
present magnetic variation.

44. 44
Selecting a VHF Antenna
Mariner 4200 is a 3dB antenna for sailboat mastheads and small powerboats. Mariner
8900 is our very best 6dB fiberglass antenna, with silver-plated elements, gold-plated
connectors and heavy-duty construction. VHF antennas are a crucial part of your VHF
installation, and understanding how they work and how to select the correct antenna can
greatly improve your ability to communicate with other boaters and shore stations. The
main purpose of a VHF antenna is to provide a radiator for the power that the transmitter
in the radio produces, and to radiate this energy in the correct direction. Antennas also
have to be enclosed in a weather-protected enclosure (or be made of a corrosion resistant
metal and plastic) and must be able to withstand the substantial forces generated by a
boat pounding in heavy seas.
SELECTION CRITERIA
dB Rating
An antenna’s dB rating (or antenna gain) indicates the apparent increase in transmitting
power due to its ability to focus energy. Antennas with a high dB rating concentrate energy
perpendicular to the antenna shaft in a field that is shaped like a disk. This makes your
radio signal appear stronger to receiving stations around you. It also reduces the amount
of energy transmitted above or below the antenna, which can be a problem if your boat is
pitching or rolling in seas. A concentrated signal can actually fade in and fade out as the
boat rolls and pitches. As the dB rating of the antenna increases, so does the height of the
antenna, but the horizontal angle diminishes. The broad radiation pattern from a low dB
antenna allows a sailboat to heel over and still send signals toward the horizon. Sailboats
should use a 3dB antenna mounted at the top of the mast whenever possible.

45. 45
Gains and losses
Customers have asked us if it’s necessary to match the antenna gain in dB to the loss (in
dB) caused by the coaxial cable inside the antenna. While the concepts are related, you
can’t trade one for another. Here’s how we explain it: A gain increase of 3dB means a
doubling of signal strength: 6dB is a fourfold increase, and 9dB is an eightfold increase.
The actual watts transmitted doesn’t increase; it’s just that the power is concentrated,
much like a reflector on a flashlight, in a more concentrated beam. Therefore, a radio with
a 6dB antenna will sound like it has a larger transmitter than the same radio with a 3dB
antenna. Coaxial cable, while efficient, loses some energy with every foot. In the West
Advisor on Selecting Coaxial Cable we’ve noted that RG-58U coax (the small stuff) loses
3dB for every 49' of run. That’s roughly the same as saying that if you have a 49' run of
cable, your radio will sound like it’s transmitting with 12.5 watts instead of 25. If you run
the same cable 98', you’ll sound like you’ve got a six-watt radio. Note that by putting your
antenna at the top of an 80' mast, even using small coax, you’ll still get very good range,
but your coax will have reduced your effective power. Therefore, it is prudent to use the
largest coax you can, especially on long runs. The trade-off is more weight aloft, which
increases heel and diminishes sailing performance, so you will have to compromise.

46. 46
BIBLOGRAPHY:
 https://www.aiportsindia.org.in
 https://www.aai.aero.org
 https://en.wikipedia.org/wiki/AAI
 material from respective departments