AIRPORT AUTHORITY OF INDIA
TRAINING REPORT
ON
“AIR TRAFFIC SERVICES”
Submitted by:
TUSHAR BHASIN
Roll No.: 15413302809
Semester: 7th
CONTENTS
1.
2.
3.
4.
5.
6.
Introduction
Acknowledgement
Main Functions of AAI
Services Provided by AAI
Air traffic Services
CNS/ATM
a. Functions of CNS
b. Airport Control
c. En-route, Center, or Area Control
7. Automation Unit
a. Objectives of Automation System
b. Types of Equipment’s used in the Unit
c. ATC working positions
d. Automation System overview
e. Software Overview
f. Automation System Description
8. VHF Unit
a. Transmitter
b. Receiver
c. Antennas
d. VCCS
e. RCAG
9. Navigational Aids Unit
a. Non-Directional Beacon (NDB)
b. VHF Omni Range (VOR)
c. Distance Measuring Equipment (DME)
d. Instrument Landing System (ILS)
e. Satellite Navigation (GAGAN)
ACKNOWLEDGEMENT
We are extremely grateful to the AIRPORT AUTHORITY OF INDIA (AAI) for
providing us with such a lifetime experience. Being one of the best organizations
in India, AAI has a highly qualified and equipped staff and it was indeed a pleasure
to perform our training under them.
The training schedule was appropriately designed for us to experience the
importance and working of each department. We would take this opportunity to
thank our training in-charge and the associated staff for a flawless execution of
their plan.
In the end, we would like to convey our gratefulness and gratitude towards the
entire AAI family who were eager enough to share their knowledge and expertise.
They gave us unparalleled support throughout the training and were a big part in
making it successful.
INTRODUCTION
The AIRPORTS AUTHORITY OF INDIA (AAI) is an organization working
under the Ministry of Civil Aviation that manages all the airports in India.
AIRPORTS AUTHORITY OF INDIA (AAI) came to existence on 1st April
1995. It was formed under the parliament act - AIRPORTS AUTHORITY OF
INDIA ACT, 1994, by merging the INTERNATIONAL AIRPORTS
AUTHORITY OF INDIA and NATIONAL AIRPORTS AUTHORITY with a
view to accelerate the integrated development, expansion and modernization of the
air traffic services, passenger terminals, operational areas and cargo facilities at the
airports in the country.
The AAI manages and operates 115 airports including 11 international airports, 81
domestic airports and 23 civil enclaves. The corporate headquarters (CHQ) are at
Rajiv Gandhi Bhawan , Safdarjung Airport, New Delhi.
MAIN FUNCTIONS OF AAI
 Control and management of the Indian air space extending beyond the
territorial limits of the country.
 Provision of communication, navigation and surveillance aids.
 Expansion and strengthening of operational areas and movement control aids
for aircrafts and vehicular traffic in operational areas.
 Design, development, operation and maintenance of passenger terminals.
 Development and management of cargo terminals at international and
domestic airports.
 Provision of passenger facilities and information system in passenger
terminals.
 Manage airports, civil enclaves and aeronautical communication.
 Plan, develop, construct, maintain runways, taxiways, Apon, terminal and
ancillary buildings, air safety services and search and rescue.
 Arranging postal money exchange, insurance and telephone facilities.
 Establish and maintain hotels/restaurants and rest rooms.
 Security arrangements and protocol/coordination.
SERVICES PROVIDED BY AAI
Airports Authority of India provides air traffic services as per AAI Act 1995.
These services are - air traffic control service, flight information service, and
alerting service. In order to achieve the objectives of air traffic services there is a
need to specify procedures necessary for the safety of air navigation for uniform
application throughout India.
Maintaining the acceptable levels of safety calls for standardization and quality
assurance in every sub systems of Air Traffic System at one end and maintaining
harmony with the ICAO standards and recommended practices at the other. A
Manual of Air Traffic Services Part I has been developed by Airports Authority of
India as a part of comprehensive documentation to achieve this objective.
The purpose of this document is to establish procedures, provide information and
instructions which are essential for the provision of safe and efficient air traffic
services in the Indian airspace and at airports where air traffic services are
provided by Airports Authority of India.
AAI provides two main services:

Air traffic services

Construction and development of airports and air routes
AIR TRAFFIC SERVICES
In aviation, an air traffic service (ATS) is an extra-ventricular service which
regulates and assists aircraft in real-time to ensure their safe operations. In
particular, ATS is to prevent collisions between aircraft; provide advice of the safe
and efficient conduct of flights; conduct and maintain an orderly flow of air traffic;
and notify concerned organizations of and assist in search and rescue operations.
The ATS further provides four services:
 air traffic control services, which is to prevent collisions in controlled
airspace by instructing pilots where to fly
 air traffic advisory service, used in uncontrolled airspace to prevent
collisions by advising pilots of other aircraft or hazards;
 flight information service, which provides information useful for the safe
and efficient conduct of flights
 Alerting service, which provides services to all known aircraft.
An ATS route is a designated route for channeling the flow of traffic as necessary
for the provision of air traffic services. This includes jet routes, area navigation
routes, and arrival and departure route. Routes may be defined with a designator; a
path to and from significant points; distance between significant points; reporting
requirements; and the lowest safe altitude.
CNS/ATM
CNS/ATM stands for Communications, Navigation and Surveillance Systems for
Air Traffic Management. This uses various systems including satellite systems,
and varying levels of automation to achieve a seamless global Air Traffic
Management system.
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:
a)
Communication: Communication is the exchange of voice and data
information between the pilot and air traffic controllers or flight information
centre.
b)
Navigation: Navigation element of CNS/ATM systems is meant to provide
accurate, reliable and seamless position determination capability to aircrafts.
c)
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 system 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 system which 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.
CNS Departments in AAI are:



CNS-Operation and Maintenance (CNS- O&M).
CNS- Planning (CNS- P).
Flight Inspection Unit & Radio construction and Development Units (FIU &
RCDU).
FUNCTIONS OF CNS:

Commissioning of the CNS equipment

Periodic inspections and surveillance of the Aeronautical Telecommunication
stations to ensure that the performance and maintenance of the CNS
equipment is in accordance with the stipulated guidelines

Scrutiny and processing of Manuals of Aeronautical Telecommunication
Stations submitted by AAI for the purpose of approval and Safety
Management Manuals in respect of such stations

Provide assistance in the establishment of Directorate of Airspace and Air
Traffic Management in DGCA for certification and formulation of related
regulation and guidance material

Any other duty assigned by DGCA from time to time particularly
Surveillance/ oversight functions.

Air Traffic Services

Surface Movement and Control

Flight Information Control

Approach Control

Area Control

Aerodrome Control
AIRPORT CONTROL:
The primary method of controlling the immediate airport environment is visual
observation from the airport traffic control tower (ATCT). The ATCT is a tall,
windowed
structure
located
on
the
airport
grounds. Aerodrome or Tower controllers are responsible for the separation and
efficient movement of aircraft and vehicles operating on the taxiways and runways
of the airport itself, and aircraft in the air near the airport, generally 5 to 10 nautical
miles (9 to 18 km) depending on the airport procedures.
Radar displays are also available to controllers at some airports. Controllers may
use a radar system called Secondary Surveillance Radar for airborne traffic
approaching and departing. These displays include a map of the area, the position
of various aircraft, and data tags that include aircraft identification, speed, altitude,
and other information described in local procedures.
The areas of responsibility for ATCT controllers fall into three general operational
disciplines; Local Control or Air Control, Ground Control, and Flight
Data/Clearance Delivery—other categories, such as Apron Control or Ground
Movement Planner, may exist at extremely busy airports. While each ATCT may
have unique airport-specific procedures, such as multiple teams of controllers
('crews') at major or complex airports with multiple runways, the following
provides a general concept of the delegation of responsibilities within the ATCT
environment.
Remote and Virtual Tower (RVT) is a system based on Air Traffic Controllers
being located somewhere other than at the local airport tower and still able to
provide Air Traffic Control services. Displays for the Air Traffic Controllers may
be either optical live video and/or synthetic images based on surveillance sensor
data.
 Ground control:
Ground Control (sometimes known as Ground Movement Control abbreviated to
GMC or Surface Movement Control abbreviated to SMC) is responsible for the
airport "movement" areas, as well as areas not released to the airlines or other
users. This generally includes all taxiways, inactive runways, holding areas, and
some transitional aprons or intersections where aircraft arrive, having vacated the
runway or departure gate. Exact areas and control responsibilities are clearly
defined in local documents and agreements at each airport. Any aircraft, vehicle, or
person walking or working in these areas is required to have clearance from
Ground Control. This is normally done via VHF/UHF radio, but there may be
special cases where other processes are used. Most aircraft and airside vehicles
have radios. Aircraft or vehicles without radios must respond to ATC instructions
via aviation light signals or else be led by vehicles with radios. People working on
the airport surface normally have a communications link through which they can
communicate with Ground Control, commonly either by handheld radio or
even cell phone. Ground Control is vital to the smooth operation of the airport,
because this position impacts the sequencing of departure aircraft, affecting the
safety and efficiency of the airport's operation.
Some busier airports have Surface Movement Radar (SMR), such as, ASDE-3,
AMASS or ASDE-X, designed to display aircraft and vehicles on the ground.
These are used by Ground Control as an additional tool to control ground traffic,
particularly at night or in poor visibility. There are a wide range of capabilities on
these systems as they are being modernized. Older systems will display a map of
the airport and the target. Newer systems include the capability to display higher
quality mapping, radar target, data blocks, and safety alerts, and to interface with
other systems such as digital flight strips.
 Local control or air control:
Local Control (known to pilots as "Tower" or "Tower Control") is responsible for
the active runway surfaces. Local Control clears aircraft for takeoff or landing,
ensuring that prescribed runway separation will exist at all times. If Local Control
detects any unsafe condition, a landing aircraft may be told to "go-around" and be
re-sequenced into the landing pattern by the approach or terminal area controller.
Within the ATCT, a highly disciplined communications process between Local
Control and Ground Control is an absolute necessity. Ground Control must request
and gain approval from Local Control to cross any active runway with any aircraft
or vehicle. Likewise, Local Control must ensure that Ground Control is aware of
any operations that will impact the taxiways, and work with the approach radar
controllers to create "holes" or "gaps" in the arrival traffic to allow taxiing traffic to
cross runways and to allow departing aircraft to take off. Crew Resource
Management (CRM) procedures are often used to ensure this communication
process is efficient and clear, although this is not as prevalent as CRM for pilots.
 Flight data / clearance delivery:
Clearance Delivery is the position that issues route clearances to aircraft, typically
before they commence taxiing. These contain details of the route that the aircraft is
expected to fly after departure. Clearance Delivery or, at busy airports, the Traffic
Management Coordinator (TMC) will, if necessary, coordinate with the en route
center and national command center or flow control to obtain releases for aircraft.
Often, however, such releases are given automatically or are controlled by local
agreements allowing "free-flow" departures. When weather or extremely high
demand for a certain airport or airspace becomes a factor, there may be ground
"stops" (or "slot delays") or re-routes may be necessary to ensure the system does
not get overloaded. The primary responsibility of Clearance Delivery is to ensure
that the aircraft have the proper route and slot time. This information is also
coordinated with the en route center and Ground Control in order to ensure that the
aircraft reaches the runway in time to meet the slot time provided by the command
center. At some airports, Clearance Delivery also plans aircraft push backs and
engine starts, in which case it is known as the Ground Movement Planner (GMP):
this position is particularly important at heavily congested airports to prevent
taxiway and apron gridlock.
Flight Data (which is routinely combined with Clearance Delivery) is the position
that is responsible for ensuring that both controllers and pilots have the most
current information: pertinent weather changes, outages, airport ground
delays/ground stops, runway closures, etc. Flight Data may inform the pilots using
a recorded continuous loop on a specific frequency known as the Automatic
Terminal Information Service (ATIS).
 Approach and terminal control:
Many airports have a radar control facility that is associated with the airport. In
most countries, this is referred to as Terminal Control; in the U.S., it is referred to
as a TRACON (Terminal Radar Approach Control.) While every airport varies,
terminal controllers usually handle traffic in a 30-to-50-nautical-mile (56 to 93 km)
radius from the airport. Where there are many busy airports close together, one
consolidated Terminal Control Center may service all the airports. The airspace
boundaries and altitudes assigned to a Terminal Control Center, which vary widely
from airport to airport, are based on factors such as traffic flows, neighboring
airports and terrain. A large and complex example is the London Terminal Control
Centre which controls traffic for five main London airports up to 20,000 feet
(6,100 m) and out to 100 nautical miles (190 km).
Terminal controllers are responsible for providing all ATC services within their
airspace. Traffic flow is broadly divided into departures, arrivals, and overflights.
As aircraft move in and out of the terminal airspace, they are handed off to the next
appropriate control facility (a control tower, an en-route control facility, or a
bordering terminal or approach control). Terminal control is responsible for
ensuring that aircraft are at an appropriate altitude when they are handed off, and
that aircraft arrive at a suitable rate for landing.
Not all airports have a radar approach or terminal control available. In this case,
the en-route center or a neighboring terminal or approach control may co-ordinate
directly with the tower on the airport and vector inbound aircraft to a position from
where they can land visually. At some of these airports, the tower may provide a
non-radar procedural approach service to arriving aircraft handed over from a radar
unit before they are visual to land. Some units also have a dedicated approach unit
which can provide the procedural approach service either all the time or for any
periods
of
radar
outage
for
any
reason.
EN-ROUTE, CENTER, OR AREA CONTROL:
ATC provides services to aircraft in flight between airports as well. Pilots fly under
one of two sets of rules for separation: Visual Flight Rules (VFR) or Instrument
Flight Rules (IFR). Air traffic controllers have different responsibilities to aircraft
operating under the different sets of rules. While IFR flights are under positive
control, in the US VFR pilots can request flight following, which provides traffic
advisory services on a time permitting basis and may also provide assistance in
avoiding areas of weather and flight restrictions. Across Europe, pilots may request
for a "Flight Information Service", which is similar to flight following. In the UK it
is known as a "Traffic Service".
En-route air traffic controllers issue clearances and instructions for airborne
aircraft, and pilots are required to comply with these instructions. En-route
controllers also provide air traffic control services to many smaller airports around
the country, including clearance off of the ground and clearance for approach to an
airport. Controllers adhere to a set of separation standards that define the minimum
distance allowed between aircraft. These distances vary depending on the
equipment and procedures used in providing ATC services.
General characteristics:
En-route air traffic controllers work in facilities called Area Control Centers, each
of which is commonly referred to as a "Center". The United States uses the
equivalent term Air Route Traffic Control Center (ARTCC). Each center is
responsible for many thousands of square miles of airspace (known as a Flight
Information Region) and for the airports within that airspace. Centers control IFR
aircraft from the time they depart from an airport or terminal area's airspace to the
time they arrive at another airport or terminal area's airspace. Centers may also
"pick up" VFR aircraft that are already airborne and integrate them into the IFR
system. These aircraft must, however, remain VFR until the Center provides a
clearance.
Center controllers are responsible for climbing the aircraft to their requested
altitude while, at the same time, ensuring that the aircraft is properly separated
from all other aircraft in the immediate area. Additionally, the aircraft must be
placed in a flow consistent with the aircraft's route of flight. This effort is
complicated by crossing traffic, severe weather, special missions that require large
airspace allocations, and traffic density. When the aircraft approaches its
destination, the center is responsible for meeting altitude restrictions by specific
points, as well as providing many destination airports with a traffic flow, which
prohibits all of the arrivals being "bunched together". These "flow restrictions"
often begin in the middle of the route, as controllers will position aircraft landing
in the same destination so that when the aircraft are close to their destination they
are sequenced.
As an aircraft reaches the boundary of a Center's control area it is "handed off" or
"handed over" to the next Area Control Center. In some cases this "hand-off"
process involves a transfer of identification and details between controllers so that
air traffic control services can be provided in a seamless manner; in other cases
local agreements may allow "silent handovers" such that the receiving center does
not require any co-ordination if traffic is presented in an agreed manner. After the
hand-off, the aircraft is given a frequency change and begins talking to the next
controller. This process continues until the aircraft is handed off to a terminal
controller ("approach").
Radar coverage:
Since centers control a large airspace area, they will typically use long range radar
that has the capability, at higher altitudes, to see aircraft within 200 nautical miles
(370 km) of the radar antenna. They may also use TRACON radar data to control
when it provides a better "picture" of the traffic or when it can fill in a portion of
the area not covered by the long range radar.
In the U.S. system, at higher altitudes, over 90% of the U.S. airspace is covered by
radar and often by multiple radar systems; however, coverage may be inconsistent
at lower altitudes used by unpressurized aircraft due to high terrain or distance
from radar facilities. A center may require numerous radar systems to cover the
airspace assigned to them, and may also rely on pilot position reports from aircraft
flying below the floor of radar coverage. This results in a large amount of data
being available to the controller. To address this, automation systems have been
designed that consolidate the radar data for the controller. This consolidation
includes eliminating duplicate radar returns, ensuring the best radar for each
geographical area is providing the data, and displaying the data in an effective
format.
Centers also exercise control over traffic travelling over the world's ocean areas.
These areas are also FIRs. Because there are no radar systems available for oceanic
control, oceanic controllers provide ATC services using procedural control. These
procedures use aircraft position reports, time, altitude, distance, and speed to
ensure separation. Controllers record information on flight progress strips and in
specially developed oceanic computer systems as aircraft report positions. This
process requires that aircraft be separated by greater distances, which reduces the
overall capacity for any given route. See for example the North Atlantic
Track system.
Some Air Navigation Service Providers (e.g. Air services Australia, The Federal
Aviation Administration, NAV CANADA, etc.) have implemented Automatic
Dependent Surveillance - Broadcast (ADS-B) as part of their surveillance
capability. This new technology reverses the radar concept. Instead of radar
"finding" a target by interrogating the transponder, the ADS-equipped aircraft
sends a position report as determined by the navigation equipment on board the
aircraft. Normally, ADS operates in the "contract" mode where the aircraft reports
a position, automatically or initiated by the pilot, based on a predetermined time
interval. It is also possible for controllers to request more frequent reports to more
quickly establish aircraft position for specific reasons. However, since the cost for
each report is charged by the ADS service providers to the company operating the
aircraft, more frequent reports are not commonly requested except in emergency
situations. ADS is significant because it can be used where it is not possible to
locate the infrastructure for a radar system (e.g. over water). Computerized radar
displays are now being designed to accept ADS inputs as part of the display. This
technology is currently used in portions of the North Atlantic and the Pacific by a
variety of states who share responsibility for the control of this airspace.
Precision approach radars are commonly used by military controllers of air forces
of several countries, to assist the Pilot in final phases of landing in places where
Instrument Landing System and other sophisticated air borne equipments are
unavailable to assist the pilots in marginal or near zero visibility conditions. This
procedure is also called Talk downs.
A Radar Archive System (RAS) keeps an electronic record of all radar
information, preserving it for a few weeks. This information can be useful for
search and rescue. When an aircraft has 'disappeared' from radar screens, a
controller can review the last radar returns from the aircraft to determine its likely
position. For example, see this crash report/ RAS is also useful to technicians who
are maintaining radar systems.
Flight traffic mapping:
The mapping of flights in real-time is based on the air traffic control system. In
1991, data on the location of aircraft was made available by the Federal Aviation
Administration to the airline industry. The National Business Aviation
Association (NBAA), the General Aviation Manufacturers Association, the
Aircraft Owners & Pilots Association, the Helicopter Association International,
and the National Air Transportation Association petitioned the FAA to
make ASDI information
available
on
a
"need-to-know"
basis.
Subsequently, NBAA advocated the broad-scale dissemination of air traffic data.
The Aircraft Situational Display to Industry (ASDI) system now conveys up-todate flight information to the airline industry and the public. Some companies that
distribute ASDI information are Flight Explorer, Flight View, and Flyte Comm.
Each company maintains a website that provides free updated information to the
public on flight status. Stand-alone programs are also available for displaying the
geographic location of airborne IFR (Instrument Flight Rules) air traffic anywhere
in the FAA air traffic system. Positions are reported for both commercial and
general aviation traffic. The programs can overlay air traffic with a wide selection
of maps such as, geo-political boundaries, air traffic control center boundaries,
high altitude jet routes, and satellite cloud and radar imagery.
AUTOMATION UNIT
Before the days of radar and computer based systems, Air Traffic Control was
dependent entirely on Procedures. The importance of calculations to determine
distance and time as well as techniques still communicated within pilots and ATC
today such as position and altitude reporting. Progress strips were passed one from
one controller to anther (a practice which can still be found today).
However the 1950’s saw early attempts with introducing automated systems into
air traffic control with the expansion of the air carrier system.
Automation system provides the air traffic controller with the information required
for the safe and efficient performance of their duties. It uses information and data
from various systems and equipments and organizes this information to best
accomplish this purpose.
The functioning of this system is known as a closed loop control theory. Where by
the system is self adjusting to the multitude of information that is it receiving, in
other words receiving feedback and adjusting its method as compared to an open
loop system where no feedback is given. Specifically for ATC, how the user wants
the system to be configured at future points depends on the objectives at the
planning stage. This can involve safety parameters that need to be input into the
system such as separation criteria. Any excursions or deviations from this set of
criteria are corrected by a controlling function through the feedback function. One
can see that communication with other system elements such as aircraft, other ATC
units and ground vehicles is key.
In addition to these variables, there are other factors that need to be considered, an
example being the external forces of weather variables and the unreliability of both
the human and non human components, which can be difficult to predict.
OBJECTIVES OF AUTOMATION SYSTEM

PRIMARY OBJECTIVES: The primary objectives of automation system is
as follows:
o
Efficiency enhancement of ATC officers: Automation system
enhances the efficiency of the air traffic controllers.
o
Accuracy of overall ATC: Automation system also takes care of the
accuracy of the air traffic controllers as well as that of the pilot.
o
Safety of passengers and aircraft: Efficiency and accuracy of air
traffic controllers directly/indirectly leads to safety of the passengers
as well as aircraft.
ALL THIS IS DONE THROUGH TIMELY ACQUISITION AND
PRESENTATION OF FLIGHT RELATED DATA FOR USE BY AIR
TRAFFIC CONTROLLERS AND SUPPORT STAFF.
TYPES OF EQUIPMENT’S IN THE UNIT
Main H/W
Configuration
Subsystem Type
Subsystem Description
RDPS
Radar data processing system
SUN FIRE-210
FDPS
Flight data processing system
SUN FIRE-210
DRF
Data recording facility
SUN FIRE-210
ATG
Air traffic generator
(ATC simulator system)
SUN FIRE-210
SDD
Situation display workstation
SUN BLADE-2500
FDD
Flight data display workstation
SUN BLADE-1500
CMD
Control and Monitoring display
workstation
SUN BLADE-1500
AIS
Aeronautical information system
SUN BLADE-1500
DRA
Direct radar access
SUN FIRE-210
DMS
Database Management system
SUN BLADE-1500
Connecting all the subsystems
CAT-5 e
Dual LAN
Network
ATC WORKING POSITIONS
The ATC working positions are the operational areas from which all air
traffic is controlled and coordinated. The ATC working positions are divided
into sectors with each sector being assigned an area of ATC responsibility
(controlling inbound traffic, outbound traffic, etc.). Each sector consists of
one or more operational working positions. The primary objective of the
working position is to provide the man-machine interface between the ATC
operational system and the user (air traffic controller) for the purpose of
controlling aircraft. Each working position is comprised of a combination of
the following display types and I/O devices, depending upon the assigned
function: situation data display (SDD), flight data display (FDD), optical
mouse, various keyboards, flight strip printer, and hard copy printer.
AUTOMATION SYSTEM OVERVIEW
The Automation System is comprised of the following functional subsystems:

Radar Data Processing System (RDPS): Receives and processes radar data
information from various radar sites.

Flight Data Processing System (FDPS): Processes information associated
with flight plan data based on information received from internal or external
sources and makes it accessible by the various Air Traffic Control (ATC)
working positions including the Flight Data Display (FDD).

Communications Gateway Processor / Aeronautical Information System
(CGP/AIS) : Subsystem which provides the interface to the Controller, Pilot
Data Link Communications as well as AFTN.

Data Recording Facility (DRF): Provides capability to record and replay
ATC data from all subsystems on the local area network (LAN) including
operator actions at each controller working position.

Data Management System (DMS): provides capability to perform adaptation
changes and downloads of new software releases.

Supervisor Working Position: Consists of a Situation Data Display (SDD)
and Control and Monitoring Display / Flight Data Display / Aeronautical
Information Display (CMD/FDD/AID). It provides a centralized point of
control for all the system management related actions and maintenance
operations. SDD displays track and flight data received from Radar Data
Processing System (RDPS). CMD provides an integrated capability for
control and monitoring of the automation components and radar interfaces.

Controller Working Position: Consists of an SDD and either an FDD/AID
or an FDD/AID/DLD and an FDD/DLD. Together these positions are used to
control aircraft that enter its assigned area of jurisdiction and monitors aircraft
flight plan progress.

Voice Processing Facility (VPF): The VPF digitizes analog audio from the
Voice Communication Control System (VCCS). This audio is typically ATC
radio or telephone communications sent through a main distribution frame
(MDF) to the VPF and then recorded by the DRF.

LAN: Critical subsystem components such as RDPS, FDPS, and DRF, are
redundant to ensure continuous operation in the event of a component failure
or maintenance action through LAN Switches. All the subsystems are
interconnected via dual 1GB Ethernet LAN except tower positions which
operate on 100MBPS. A third LAN provides Direct Radar Access (DRA).
SYSTEM OVERVIEW:
The Air traffic Control (ATC) Automation System (ATCAS) is comprised of
numerous computers linked by a dual LAN, that together accomplish the tasks of
accepting and processing radar and flight plan data and displaying meaningful
ATC-related information and operational display for use by ATCAS personnel.
The number of operational workstations in the ATCAS depends on customer
requirements. While typically there are multiple FDDs, CMDs and SDDs in the
ATCAS, only one DMS is needed to maintain the system’s adaption data.
The interrelationship of these computers, LANS, flight plan data, and radar data is
illustrated in the ATCAS block diagram. Operational workstations are connected
by dual-redundant LANs to dual-redundant FDPS, DRF, and RDPS subsystems. In
addition, a single DRA subsystem, which is a radar processor similar to the RDPS,
provides an independent mechanism and signal path to the SDDs. The DRA
channel can be used as a back-up in the event that both RDPSs (or the dual LANs)
fail.
The DMS runs on a SUN computer and has the primary function of managing
adaption data required by the ATCAS.
SOFTWARE OVERVIEW
Functions are controlled and executed by computer software application programs
that reside in the Automation System computers. The Sun Solaris Operating
System (OS) runs the application programs and acts as an interface between the
controller and application. The OS manages computer resources in a noninterfering manner, executing stored applications and controlling information
transfers between processors and external devices and interfaces via the LAN. The
application software is organized by function into Computer Software
Configuration Items (CSCls).
The application software references site-specific adaptation data.
Commercial Off-the-Shelf (COTS) products are used in the Automation System.
The Automation System consists of COTS hardware and software components and
Raytheon's AutoTrac II Software, adapted specifically for use in the Automation
System.
AUTOMATION SYSTEM DESCRIPTION
Each section includes a block diagram of each subsystem's hardware, a brief
description of the hardware and associated interfaces, and an overview of the
executable software.
Critical processing systems such as RDPS, FDPS, and DRF have redundant
processors to eliminate the chance of a single point of failure disrupting critical Air
Traffic Control (ATC) functions.
All processing systems are interconnected via a dual 100BaseT/1000BaseT
Ethernet LAN. An optional third LAN is available to provide Direct Radar Access.
The Automation System comprises of the following functional subsystems:

Local Area Network (LAN): The LAN connects all of the servers and
workstations so that information can be shared by all. In the event that a LAN
should fail, a second LAN is provided and becomes operational in the event
the primary LAN becomes inoperative. These LANs are designated LAN A
and LAN B. LAN A and LAN B connect to all servers and workstations.
Additionally, the option for a third LAN, LAN C, exists. This LAN connects
only to the Direct Radar Access (DRA) subsystem and all Situation Data
Displays (SDD). In the event that both LAN A and LAN B fail this LAN C
provides the minimum necessary information to continue operations until
either of LAN A or LAN B become available again.
o Local Area Network Hardware and Interface Description: The LAN
consists of 3 Ethernet switches. The number of ports on these switches
is dependent on the number of nodes in the system. Additional
switches may be necessary based on the number of nodes in the
system or specific design specifications. Each Sun workstation/server
has a built-in 10/100/1000 Ethernet port for LAN A and either a builtin 10/100/1000 Ethernet port or a 10/100/1000 Ethernet PCI adapter
for LAN B. If it is an adapter, it is mounted within the SUN processor
in a Peripheral Component Interconnection (PCI) slot. Each LAN
o
connection is connected via a Category 5e cable with a RJ-45
connector.
Local Area Network Software Description: The operation of all LANrelated communication is controlled by the Network Operating
System (NOS) software. NOS software, which executes in every
subsystem except the DMS subsystem, is a layer on top of the UNIX
multi-tasking operating system. NOS provides a function layer for
other application software to gain access to the operating system
services in a controlled manner. NOS also provides applications with
a consistent interface for local and remote network communications.

Time Reference System (TRS): The operation of all LAN-related
communication is controlled by the Network Operating System (NOS)
software. NOS software, which executes in every subsystem except the DMS
subsystem, is a layer on top of the UNIX multi-tasking operating system. NOS
provides a function layer for other application software to gain access to the
operating system services in a controlled manner. NOS also provides
applications with a consistent interface for local and remote network
communications.

Radar Data Processing System (RDPS): The main purpose of the RDPS is
to process radar data. This includes returns consisting of both Primary
Surveillance Radar (PSR) and Secondary Surveillance Radar (SSR) track
data from detected aircraft. The Radar Data Processor (RDP) filters this data
and provides it to the tracking function, which uses the radar data to update
the track data maintained on each aircraft. The principal outputs of the RDPS
are target track and flight plan data, which the RDPS supplies to the Situation
Data Displays (SDDs) via the LAN. The RDPS also generates status
information and reports for display at the Control and Monitoring Display
(CMD) and makes data available for recording at the Data Recording Facility
(DRF). The RDPS provides redundancy with an active and standby Radar
Data Processor (RDP); each equipped with its own set of radar interfaces. In
the event of failure of the active RDP, the standby RDP will automatically
assume the active functions. The System Monitoring and Control (SMC)
software monitors the health of the RDPS and upon detection of a failure of
the active subsystem, causes a switchover to occur.
o RDPS Hardware and Interface Description: Each RDPS consists of a
SUN workstation/server and each RDPS also contains a Time and
Frequency Processor card that accepts an IRIG-B signal supplied by
the Time Reference System (TRS). This permits each RDPS to be
synchronized to Global Positioning System (GPS) or Universal Time
Coordinated (UTC) time.
o RDPS Software Description: The RDPS executes the RDP software.
Some functions of the RDP software also run in the Situation Data
Display (SDD) and Flight Data Display (FDD) processors in order to
support maintenance of the flight plan data within these subsystems.

Flight data Processing System (FDPS): The main purpose of the FDPS is to
create and update flight plans based on information received from external
sources/ these external sources of data include inputs from Flight Data
Display (FDD) positions and Air Traffic Services (ATS) messages received
via the Aeronautical Fixed Telecommunications Network (AFTN)
interface.
In addition, the FDPS is capable of analyzing flight plan routes, performing
flight plan conversion, calculating flight trajectory and estimated times,
determining flight plan status, validating flight plans, displaying and/or
printing flight plan data, providing automatic and manual Secondary
Surveillance Radar (SSR) code allocation, processing Meteorological
(MET) data, and automatically updating flight plans based on Estimated
Time Over (ETO) provided from the Radar Data Processor (RDP).
The FDPS provides redundancy with an active and standby Flight Data
Processor (FDP). In normal operation, one FDP is active and the other is in
standby. In the event of failure of the active FDP, the standby FDP will
automatically assume the active functions. The System Monitoring and
Control (SMC) software monitors the health of the FDPS and upon detection
of a failure of the active subsystem, causes a switchover to occur.
o
o
FDPS Hardware and Interface Description: Each FDP processor
consists of a SUN workstation/server.
FDPS Software Description: Each FDPS executes FDP software,
which performs the processing required to establish and maintain the
flight plan database. The four major functions of FDP software are
Flight Plan Data Management, Supplemental Information
Management, Flow Control Management, and FDPS Control.

Data Recording Facility (DRF): The DRF records and allows the replay of
Air Traffic Control (ATC) data. Data is recorded from all subsystems onto
Digital Audio Tape (DAT) and hard disk. Two types of playback supported
by the DRF can be selected at the Control and Monitoring Display (CMD),
either a playback of previously recorded data targeted for a particular
playback Situation Data Display (SDD), or a printed log of operator inputs,
system messages, and certain list updates as they occurred at the CMD or
Flight Data Display (FDD) workstation positions. SDD playback provides a
visual replay of events recorded as they occurred at the selected SDD. The
SDD operator can control the presentation of the playback data via freeze and
unfreeze requests to the DRF.
For redundancy, there are an active and a standby DRF. In the event of failure
of the active DRF, the standby DRF will automatically assume the active
functions.

Operational Controller Position: The primary function of the Operational
Controller Position is to control aircraft that enters its assigned area of
jurisdiction and to monitor aircraft flight plan progress. The position
integrates radar and non-radar ATC functions and communications facilities
into a single console.

Tower Position: The primary function of the Tower Position is to monitor air
traffic in the immediate area.

Control and Monitoring Display (CMD): The CMD console provides an
integrated capability for control and monitoring of the automation components
and radar. It provides an interface to the operator so that the operator may
monitor, make changes, or control the system configuration. The operations
that may be performed at a CMD workstation depend on the log in status and
the authorization assigned to the operator at the workstation. The
authorizations that may be assigned are technical supervisor or operational
supervisor.

Supervisor Position:
Supervisor Position Hardware and Interface Description: The supervisor
console typically consists of SDD, and CMD/FDD/AID. Each component
consists of a Sun workstation/server as well as a keyboard and a mouse. On
the SDD, there is a Graphics Card that drives a Display.
On the CMD/FDD/AID a display is connected to the built-in video on the
system board. A printer is connected to the serial port via a custom RS-232
Null Modem cable. CMD/FDD/AID is described in a previous section.

Data Management System (DMS): The DMS serves as an off-line
workstation (not necessary for ATC operation) for generating and preparing
site adaption parameters that tailor systems operations to a segment. The
graphical user interface permits the creation and modification of geographical
data, input and updating of database records, and inputting archived data files
from the DRF. Output to a printer is also supported.
Data includes airspace files (airport and airways), equipment files (radar and
altimeters), sectorization files, systems files (display configurations), and
secondary Surveillance Radar (SSR) codes. Presentation and editing of
graphical data includes maps, filters, sectors, and radar mosaic tiles. Graphical
data is edited using a mouse and keyboard, accessing data in latitude and
longitude coordinated.
VHF UNIT
The allocated frequency range for VHF communication is 108-156 MHz. Of this,
AAI operates in the range of 117.975-136 MHz. Each airport operational under
AAI has been designated a frequency range. This division is termed as horizontal
division. The Safdarjung Airport communicates at 122.3 MHz.
The administration of the Indian Air Space is divided into Flight Information
Regions (FIRs). There are four major FIRs – New Delhi, Kolkata, Chennai and
Mumbai. Each of the FIRs extends till about 200 nautical miles.
Administration within these 200 nautical miles is also subdivided into Area,
Approach and Tower Control. Maximum catering of Air Traffic is in Approach
Region.
Tower (upto 6NMs)
Area (upto 200NMs)
Approach (upto 25NMs)
Each subdivision sends signals at a particular frequency to avoid any kind of
interference. In the Approach subdivision, the aircraft is placed in different Air
Flight levels to avoid any clash. Hence, approach needs more frequencies. In order
to have an uninterrupted communication, each level is allocated multiple
frequencies, to be used as standby.
Two basic equipments required for VHF communication:
a) Transmitter
b) Receiver
The transmitter and receiver consist of two tuned circuits each, all four tuned to the
same frequency.

Transmitter:
The transmitter is an electronic device, which usually with the aid of the antenna
propagates an electromagnetic signal. A normal radio frequency transmitter uses a
balanced modulator.
In a balanced modulator, a signal is modulated using two carriers that are 180
degrees out of phase. The resulting signals are then combined in such a way that
the carrier components cancel, leaving a DSB-SC (double sideband, suppressed
carrier) signal.
A balanced modulator is a device that modifies a signal; usually in the form of
amplitude modulated (AM) radio signal. It takes the original signal that has both
sidebands and a carrier signal, and then modulates it so that only the sideband
signals come through the output of the balanced modulator. This creates a balanced
signal, as there is less noise because the carrier signal has been removed.
Amplitude modulation is a way for a signal to be transmitted over distances. It is
the most commonly modified signal for use with a balanced modulator.
Understanding how it works will demonstrate how a balanced modulator works.
The AM signal is originally sent with a carrier signal in the form of a wave. The
wave is then modulated, or changed, by an audio signal that is also in the form of a
wave. This produces a signal that has the original carrier signal plus two bands,
one on top of the original signal and one on the bottom. These are referred to as
sidebands and are exact copies of each other. A signal like this is called a doublesideband amplitude modulated (DSB-AM) signal.
The sidebands, because they were modified by the originating audio waveform, are
the signals responsible for carrying the information that is being transmitted. Once
modulated, the carrier signal doesn’t serve a real practical purpose anymore, and it
only shows that a signal is being sent. It does, however, take up a larger chunk of
power than the two sideband signals, and also creates a less-clear signal.
To remedy, or modulate, this situation, a balanced modulator would be used. The
balanced modulator removes or suppresses the carrier signal, so that only the two
sideband signals remain. The signal that remains now has several times more
power because the carrier signal is not there to drain it away. This type of signal is
referred to as double-sideband suppressed-carrier (DSBSC). In addition to being
more powerful, the signal is also “cleaner” as it has less signal noise, which the
carrier signal can often create.
At some point, a DSBSC signal needs to have its carrier signal regenerated. This
will allow for the signal to be put back into its original form for reception. In the
case of an AM signal, it allows the signal to be received on the proper frequency
and be heard. This can be taken care of by a device such as a beat frequency
oscillator.

Receiver:
The receiver units used for the radio communication purposes of AAI typically use
a Superheterodyne Receiver.
In electronics, a *superheterodyne receiver*(sometimes shortened to *superhet*)
uses frequency mixing or heterodyning to convert a received signal to a fixed
intermediate frequency , which can be more conveniently processed than the
original radio carrier frequency. Virtually all modern radio and television receivers
use the superheterodyne principle.
The principle of operation of the superheterodyne receiver depends on the use of
heterodyning or frequency mixing . The signal from the antenna is filtered
sufficiently at least to reject the "image frequency” and possibly amplified. A local
oscillator in the receiver produces a sine wave which mixes with that signal,
shifting it to a specific intermediate frequency (IF), usually a lower frequency. The
If signal is itself filtered and amplified and possibly processed in additional ways.
The demodulator uses the IF signals rather than the original radio frequency to
recreate a copy of the original modulation (such as audio).
The following essential elements are common to all superhet circuits: a receiving
antenna , a tuned stage which may optionally contain amplification (RF amplifier),
a variable frequency local oscillator , a frequency mixer , a band pass filter and
intermediate frequency (IF) amplifier, and a demodulator plus additional circuitry
to amplify or process the original audio signal (or other transmitted information).
To receive a radio signal, a suitable antenna is required. This is often built into a
receiver; especially in the case of AM broadcast band radios. The output of the
antenna may be very small, often only a few micro volts. The signal from the
antenna is tuned and may be amplified in a so-called radio frequency (RF)
amplifier, although this stage is often omitted. One or more tuned circuits at this
stage block frequencies which are far removed from the intended reception
frequency. In order to tune the receiver to a particular station, the frequency of the
local oscillator is controlled by the tuning knob. Tuning of the local oscillator and
the RF stage may use a variable capacitor, or varicap diode. The tuning of one (or
more) tuned circuits in the RF stage must track the tuning of the local oscillator.
The signal is then fed into a circuit where it is mixed with a sine wave from a
variable frequency oscillator known as the local oscillator (LO). The mixer uses a
non-linear component to produce both sum and difference beat frequencies signals,
each one containing the modulation contained in the desired signal. The output of
the mixer may include the original RF signal at fd, the local oscillator signal at fLO,
and the two new frequencies fd+fLO and fd-fLO. The mixer may inadvertently
produce additional frequencies such as 3rd- and higher-order inter-modulation
products. The undesired signals are removed by the IF band pass filter , leaving
only the desired offset IF signal at fIF which contains the original modulation
(transmitted information) as the received radio signal had at fd.
The stages of an intermediate frequency amplifier are tuned to a particular
frequency not dependent on the receiving frequency; it greatly simplifies
optimization of the circuit. The IF amplifier (or IF strip) can be made highly
selective around its center frequency fIF, whereas achieving such a selectivity at a
much higher RF frequency would be much more difficult. By tuning the frequency
of the local oscillator fLO, the resulting difference frequency fLO - fd (or fd-fLO when
using low-side injection) will be matched to the IF amplifier's frequency fIF for the
desired reception frequency fd. One section of the tuning capacitor will thus adjust
the local oscillator's frequency fLO to (fd + fIF) while the RF stage is tuned to fd.
Engineering the multi-section tuning capacitor (or varactors ) and coils to fulfill
this condition across the tuning range is known as Tracking.
Other signals produced by the mixer (such as due to stations at nearby frequencies)
can be very well filtered out in the IF stage, giving the superheterodyne receiver its
superior performance. However, if fLO is set to fd + fIF, then an incoming radio
signal at fLO + fIF will also produce a heterodyne at fIF; this is called the image
frequency and must be rejected by the tuned circuits in the RF stage. The image
frequency is 2fIF higher (or lower) than fd, so employing a higher IF frequency fIF
increases the receiver's image rejection without requiring additional selectivity in
the RF stage.
Usually the intermediate frequency is lower than the reception frequency fd, but in
some modern receivers it is more convenient to first convert an entire band to a
much higher intermediate frequency; this eliminates the problem of image
rejection. Then a tunable local oscillator and mixer convert that signal to a second
much lower intermediate frequency where the selectivity of the receiver is
accomplished. In order to avoid interference to receivers, licensing authorities will
avoid assigning common IF frequencies to transmitting stations. Standard
intermediate frequencies used are 455 kHz for medium-wave AM radio, 10.7 MHz
for broadcast FM receivers, 38.9 MHz (Europe) or 45 MHz (US) for television,
and 70 MHz for satellite and terrestrial microwave equipment.
In early superhets, the IF stage was often a regenerative stage providing the
sensitivity and selectivity with fewer components. Such superhets were called
super-gainers or regenerodynes.
The IF stage includes a filter and/or multiple tuned circuits in order to achieve the
desired selectivity . This filtering must therefore have a band pass equal to or less
than the frequency spacing between adjacent broadcast channels. Ideally a filter
would have a high attenuation to adjacent channels, but maintain a flat response
across the desired signal spectrum in order to retain the quality of the received
signal. This may be obtained using one or more dual tuned IF transformers, or a
multipole ceramic crystal filter.
The received signal is now processed by the demodulator stage where the audio
signal (or other baseband signal) is recovered and then further amplified. AM
demodulation requires the simple rectification of the RF signal (so-called envelope
detection), and a simple RC low pass filter to remove remnants of the intermediate
frequency. FM signals may be detected using a discriminator, ratio detector , or
phase-locked loop . Continuous wave (Morse code) and single sideband signals
require a product detector using a so-called beat frequency oscillator , and there
are other techniques used for different types of modulation . The resulting audio
signal (for instance) is then amplified and drives a loudspeaker.
When high-side injection has been used, where the local oscillator is at a higher
frequency than the received signal (as is common), then the frequency spectrum of
the original signal will be reversed. This must be taken into account by the
demodulator (and in the IF filtering) in the case of certain types of modulation such
as single sideband.
Generally, instead of using a separate transmitter and receiver and a constricted
version called a Transceiver is used on either sides. This can be used to both
transmit and receive the amplitude modulated signal.
Antennas:
Two types of antennas are used:
1. Omni directional Antenna
2. Directive Antenna
In order to avoid a ‘black zone’ and simultaneous loss of communication, each
operational frequency has a Directive and an Omni - directional antenna.
Directive Antenna
Omni-directional Antenna
VCCS:
The VHF unit also contains Voice Communication Control and Switching
equipment (VCCS). The Voice Communications and Control System (VCCS) is a
solid state, modular, and flexible system which has provided reliable ATC
communications for over twenty years. The basic premise of the design is to
provide the Air Traffic Controller with a functional system tailored to his needs.
The system provides the controller with single button selection of radio channels
for transmit and receive. It also provides 'monitor only' as well as headset and/or
microphone loudspeaker functions. Use of intercoms, hot line, and airport
telephone access are also part of the system. Channel selected and channel in use
are readily visible day and night. Interposition lockout is available to prevent two
operators inadvertently using the same radio channel at the same time. Incoming
RF signals are visually and audibly apparent with the frequency displayed. The
following is a list of the VCCS sub-systems:








Radio Channel Control
Intercommunications
Telephone
Crash Alarm & Control
Clock
Test Unit
Power Supply
Meteorological
RCAG:
While VHF communication due to being line-of-sight is restricted only till the 200
nautical miles region, sometimes even less, the intermediate communication
between the aircraft and ground stations takes place using Extended VHF, also
called ‘Radio Communication Air to Ground’ (RCAG).
In this case, the original frequency and message transmitted from the base station
is also transmitted from an intermediate station and is fed to the intermediate
stations via trunk lines. Hence, the intermediate station also requires a local
transmitter. The trunk line used is an optical fiber cable which provides a
negligible delay of 20ms.
The other specifications kept in mind while transmitting AM signals are that there
Voltage Standing Wave Ratio (VSWR) must remain in between 1 and 2, generally,
1.3. Also, according to the ICAO specifications, the modulation percentage is no
more than 30%.
The Safdarjung Airport incorporates low level modulation and uses an OTE
receiver. The advantage of an OTE transmitter over others is that it can transmit
both voice (audio) as well as data signals.
All such communication between the pilot and the controller is duly recorded for
future references. Two companies provide equipments for these services –
Marathon and Ricochet. Marathon can only record the audio communication while
Ricochet is capable of recording both audio as well as the visual data. One more
important feature at the Safdarjung Airport is that it uses Vertical Polarization.
NAVIGATIONAL AIDS UNIT
Navigation plays one of the most important roles during the flight of an aircraft.
The basic principles of air navigation are identical to general navigation, which
includes the process of planning, recording, and controlling the movement of a
craft from one place to another.
Successful air navigation involves piloting an aircraft from place to place without
getting lost, breaking the laws applying to aircraft, or endangering the safety of
those on board or on the ground. Air navigation differs from the navigation of
surface craft in several ways: Aircraft travel at relatively high speeds, leaving less
time to calculate their position en route. Aircraft normally cannot stop in mid-air to
ascertain their position at leisure. Aircraft are safety-limited by the amount of fuel
they can carry; a surface vehicle can usually get lost, run out of fuel, then simply
await rescue. There is no in-flight rescue for most aircraft. And collisions with
obstructions are usually fatal. Therefore, constant awareness of position is critical
for aircraft pilots.
The techniques used for navigation in the air will depend on whether the aircraft is
flying under the visual flight rules (VFR) or the instrument flight rules (IFR). In
the latter case, the pilot will navigate exclusively using instruments and radio
navigation aids such as beacons, or as directed under radar control by air traffic
control. In the VFR case, a pilot will largely navigate using dead reckoning
combined with visual observations with reference to appropriate maps. This may
be supplemented using radio navigation aids. Interestingly, the Safdarjung Airport,
handling the VVIP flights makes use of only VFR, whereas the Indira Gandhi
International Airport involves extensive usage of both VFR and IFR.
The generally employed navigational aids are:
1.
2.
3.
4.
Non Directional Beacons (NDB)
VHF Omni Range (VOR)
Distance Measuring Equipment (DME)
Instrument Landing System (ILS)
5. Satellite Navigation
NON DIRECTIONAL BEACON (NDB)
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).
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 which specifies that NDBs be
operated on a frequency between 190 kHz and 1750 kHz. Each NDB is identified
by a one, two, or three-letter Morse code call-sign. An aircraft has a direction
finder in the cockpit for the reception of the NDB signal. Hence, it only has to head
towards the NDB.
NDB
VHF OMNI RANGE (VOR)
VOR, short for VHF omni-directional radio range, is a type of short-range
radio navigation system for aircrafts, 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 VOR 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.
VOR stations broadcast a VHF radio composite signal including the station's
identifier, voice (if equipped), and navigation signal. The identifier is typically
a two- or three-letter string in Morse code. The voice signal, if used, is usually
the station name, in-flight recorded advisories, or live flight service
broadcasts. The navigation signal allows the airborne receiving equipment to
determine a magnetic bearing from the station to the aircraft (direction from
the VOR station in relation to the Earth's magnetic North at the time of
installation). VOR stations in areas of magnetic compass unreliability are
oriented with respect to True North.
The CDI equipment used in the cockpit of aircrafts is in accordance to the
VOR. The needle in the CDI has to be followed by the aircraft. The left or
right direction is given by the OBS (Omni Bearing Status).
VHF Omni Range (VOR)
DISTANCE MEASURING EQUIPMENT (DME)
Distance measuring equipment (DME) is a transponder-based radio navigation
technology that measures slant range distance by timing the propagation delay
of VHF radio signals. DME is similar to secondary radar, except in reverse.
Aircraft use DME to determine their distance from a land-based transponder
by sending and receiving pulse pairs - two pulses of fixed duration and
separation. The ground stations are typically co-located with VORs. A typical
DME ground transponder system for en-route or terminal navigation will have
a 1 kW peak pulse output on the assigned VHF channel.
A low-power DME can also be co-located with an ILS glide slope antenna
installation where it provides an accurate distance to touchdown function,
similar to that otherwise provided by ILS Marker Beacons. a DME, in short,
enables an aircraft to establish its range from ground stations.
INSTRUMENT LANDING SYSTEMS (ILS)
An instrument 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 nav- aids and 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
Instrument landing system (ILS) facilities are a highly accurate and dependable
means of navigating to the runway in IFR conditions. When using the ILS, the
pilot determines aircraft position primarily by reference to instruments. The
ILS consists of:
a.
b.
c.
d.
the localizer transmitter;
the glide path transmitter;
the outer marker (can be replaced by an NDB or other fix);
the approach lighting system.
ILS is the primary international precision approach system approved by ICAO and
protected until 2010. ILS provides an aircraft with precision horizontal and vertical
guidance to the runway.
Localizer:
The primary component of the ILS is the localizer, which provides lateral
guidance. The localizer is a VHF radio transmitter and antenna system using the
same general range as VOR transmitters (between 108.10 MHz and 111.95 MHz).
Localizer frequencies, however, are only on odd-tenths, with 50 kHz spacing
between each frequency. The transmitter and antenna are on the centerline at the
opposite end of the runway from the approach threshold.
The localizer back course is used on some, but not all ILS systems. Where the back
course is approved for landing purposes, it is generally provided with a 75 MHz
back marker facility or NDB located 3 to 5 NM from touchdown. The course is
checked periodically to ensure that it is positioned within specified tolerances.
The signal transmitted by the localizer consists of two vertical fan-shaped patterns
that overlap, at the center. They are aligned with the extended centerline of the
runway. The right side of this pattern, as seen by an approaching aircraft, is
modulated at 150 Hz and is called the "blue" area. The left side of the pattern is
modulated at 90 Hz and is called the "yellow" area. The overlap between the two
areas provides the on-track signal.
The width of the navigational beam may be varied from approximately 3º to 6º,
with 5º being normal. It is adjusted to provide a track signal approximately 700 ft
wide at the runway threshold. The width of the beam increases so that at 10 NM
from the transmitter, the beam is approximately one mile wide.
Glide Path:
The glide slope provides vertical guidance to the pilot during the approach. The
ILS glide slope is produced by a ground-based UHF radio transmitter and antenna
system, operating at a range of 329.30 MHz to 335.00 MHz, with a 50 kHz spacing
between each channel. The transmitter is located 750 to 1,250 feet (ft) down the
runway from the threshold, offset 400 to 600 ft from the runway centerline.
Monitored to a tolerance of ± 1/2 degree, the UHF glide path is "paired" with (and
usually automatically tuned by selecting) a corresponding VHF localizer
frequency.
Like the localizer, the glide slope signal consists of two overlapping beams
modulated at 90 Hz and 150 Hz. Unlike the localizer, however, these signals are
aligned above each other and are radiated primarily along the approach track. The
thickness of the overlap area is 1.4º or .7º above and .7º below the optimum glide
slope.
This glide slope signal may be adjusted between 2º and 4.5º above a horizontal
plane. A typical adjustment is 2.5º to 3º, depending upon such factors as
obstructions along the approach path and the runway slope.
ILS Beacon Markers:
Instrument landing system marker beacons provide information on distance from
the runway by identifying predetermined points along the approach track. These
beacons are low-power transmitters; that operate at a frequency of 75 MHz with 3
W or less rated power output. They radiate an elliptical beam upward from the
ground. At an altitude of 1,000 ft, the beam dimensions are 2,400 ft long and 4,200
ft wide. At higher altitudes, the dimensions increase significantly.

Outer Marker: The outer marker is normally located 7.2 kilometres (3.9 nmi;
4.5 mi) from the threshold except that, where this distance is not practical, the
outer marker may be located between 6.5 to 11.1 kilometres (3.5 to 6.0 nmi;
4.0 to 6.9 mi) from the threshold. The modulation is repeated Morse-style
dashes of a 400 Hz tone. The cockpit indicator is a blue lamp that flashes in
unison with the received audio code. The purpose of this beacon is to provide
height, distance and equipment functioning checks to aircraft on intermediate
and final approach.

Middle Marker: The middle marker should be located so as to indicate, in low
visibility conditions, the missed approach point, and the point that visual
contact with the runway is imminent, ideally at a distance of approximately
3,500 ft (1,100 m) from the threshold. It is modulated with a 1.3 kHz tone as
alternating Morse-style dots and dashes at the rate of two per second. The
cockpit indicator is an amber lamp that flashes in unison with the received
audio code.

Inner Marker: The inner marker, when installed, shall be located so as to
indicate in low visibility conditions the imminence of arrival at the runway
threshold. This is typically the position of an aircraft on the ILS as it reaches
Category II minima. Ideally at a distance of approximately 1,000 ft (300 m)
from the threshold. The modulation is Morse-style dots at 3 kHz. The cockpit
indicator is a white lamp that flashes in unison with the received audio code.
The Lighting System:
Various runway environment lighting systems serve as integral parts of the ILS
system to aid the pilot in landing. Any or all of the following lighting systems may
be provided at a given facility:

approach lights

runway threshold lights

touchdown zone lights

centerline lights

runway edge lights

runway end lights

all stop bars and lead-on lights

essential taxiway lights
Principle of Operation
An ILS consists of two independent sub-systems, one providing lateral guidance
(localizer), the other vertical guidance (glide slope or glide path) to aircraft
approaching a runway. Aircraft guidance is provided by the ILS receivers in the
aircraft by performing a modulation depth comparison.
The emission patterns of the localizer and glide slope signals. Note that the glide
slope beams are partly formed by the reflection of the glide slope aerial in the
ground plane.
A localizer (LOC, or LLZ until ICAO designated LOC as the official acronym)
antenna array is normally located beyond the departure end of the runway and
generally consists of several pairs of directional antennas. Two signals are
transmitted on one out of 40 ILS channels in the carrier frequency range between
108.10 MHz and 111.95 MHz (with the 100 kHz first decimal digit always odd, so
108.10, 108.15, 108.30, and so on are LOC frequencies but 108.20, 108.25,
108.40, and so on are not). One is modulated at 90 Hz, the other at 150 Hz and
these are transmitted from separate but co-located antennas. Each antenna
transmits a narrow beam, one slightly to the left of the runway centerline, the other
to the right.
The localizer receiver on the aircraft measures the difference in the depth of
modulation (DDM) of the 90 Hz and 150 Hz signals. For the localizer, the depth of
modulation for each of the modulating frequencies is 20 percent. The difference
between the two signals varies depending on the position of the approaching
aircraft from the centerline.
If there is a predominance of either 90 Hz or 150 Hz modulation, the aircraft is off
the centerline. In the cockpit, the needle on the horizontal situation indicator (HSI,
the instrument part of the ILS), or course deviation indicator (CDI), will show that
the aircraft needs to fly left or right to correct the error to fly down the center of the
runway. If the DDM is zero, the aircraft is on the centerline of the localizer
coinciding with the physical runway centerline.
A glide slope (GS) or glide path (GP) antenna array is sited to one side of the
runway touchdown zone. The GP signal is transmitted on a carrier frequency
between 328.6 and 335.4 MHz using a technique similar to that of the localizer.
The centerline of the glide slope signal is arranged to define a glide slope of
approximately 3° above horizontal (ground level). The beam is 1.4° deep; 0.7°
below the glide slope centerline and 0.7° above the glide slope centerline.
These signals are displayed on an indicator in the instrument panel. This
instrument is generally called the omni-bearing indicator or nav indicator. The
pilot controls the aircraft so that the indications on the instrument (i.e., the course
deviation indicator) remain centered on the display. This ensures the aircraft is
following the ILS centre line (i.e., it provides lateral guidance). Vertical guidance,
shown on the instrument by the glide slope indicator, aids the pilot in reaching the
runway at the proper touchdown point. Many aircraft possess the ability to route
signals into the autopilot, allowing the approach to be flown automatically by
the autopilot.
Instrument Landing System (ILS) at IGI Airport

Airports authority of India has installed 6 ILS systems for serving both the
ends of all the three Runways at IGI Airport, Delhi.

The Runways 09, 10 and 27 are equipped with CAT I ILS and Runways 29,
28 and 11 are equipped with CAT III ILS enabling low visibility (up to 50
meters) aircraft operations during adverse weather.

During routine air calibration of CAT-III ILS for Runway 28 in July 2011, a
minor deflection in the ILS signal has been observed in the final landing phase
before the touchdown point on Runway, which does not support the CAT-III
landing requirements.

However, the ILS system as a whole and the signal in totality meets the CAT
III specifications.

The probable cause of the deflection is primarily due to buildings or structures
that have recently come up or under construction in the close proximity of
runway.

The technical experts on the subject also opine the same and have suggested
some modification in the existing buildings/structures. DIAL Authorities are
required to implement the modifications as recommended by the experts, in
the next three to four days.

On implementation of the modification by DIAL, flight calibration would be
carried out to ascertain the signal specifications and on elimination of the said
deflection, the ILS system would be restored for CAT III operations for
Runway 28.

However, ILS for Runway 29 and 11 continue to support CAT III operations
at IGI Airport, Delhi.
SATELLITE NAVIGATION
A satellite navigation or SAT NAV system is a system of satellites that provide
autonomous geo-spatial positioning with global coverage. It allows small
electronic receivers to determine their location (longitude, latitude, and altitude) to
within a few metres using time signals transmitted along a line-of-sight by radio
from satellites. Receivers calculate the precise time as well as position, which can
be used as a reference for scientific experiments. A satellite navigation system with
global coverage may be termed a global navigation satellite system or GNSS.
The GPS aided geo augmented navigation or GPS and geo-augmented
navigation system (GAGAN) is a planned implementation of a regional satellitebased augmentation system (SBAS) by the Indian government. It is a system to
improve the accuracy of a GNSS receiver by providing reference signals.
The AAI’s efforts towards implementation of operational SBAS can be viewed as
the first step towards introduction of modern communication, navigation,
surveillance/Air Traffic Management system over Indian airspace.
Technology Demonstration:
A national plan for satellite navigation including implementation of Technology
Demonstration System (TDS) over the Indian air space as a proof of concept had
been prepared jointly by Airports Authority of India (AAI) and ISRO. TDS was
successfully completed during 2007 by installing eight Indian Reference Stations
(INRESs) at eight Indian airports and linked to the Master Control Center (MCC)
located near Bangalore. Preliminary System Acceptance Testing has been
successfully completed in December 2010. The ground segment for GAGAN,
which has been put up by the Raytheon, has 15 reference stations scattered across
the country. Two mission control centres, along with associated uplink stations,
have been set up at Kundalahalli in Bangalore. One more control centre and uplink
station are to come up at Delhi. As a part of the programme, a network of 18 total
electron content (TEC) monitoring stations were installed at various locations in
India to study and analyse the behaviour of the ionosphere over the Indian region.
GAGAN's TDS signal in space provides a three-metre accuracy as against the
requirement of 7.6 metres. Flight inspection of GAGAN signal is being carried out
at Kozhikode, Hyderabad, Nagpur and Bangalore airports and the results have been
satisfactory so far.
Study of Ionosphere:
One essential component of the GAGAN project is the study of the ionospheric
behavior over the Indian region. This has been specially taken up in view of the
rather uncertain nature of the behavior of the ionosphere in the region. The study
will lead to the optimization of the algorithms for the ionospheric corrections in the
region.
To study the ionospheric behavior more effectively over entire Indian airspace,
Indian universities and R&D labs, which are involved in the development of
regional based ionotropic model for GAGAN, have suggested nine more TEC
stations.
Technology Integration:
GAGAN after its final operational phase completion will be compatible with other
SBAS systems such as the Wide Area Augmentation System (WAAS),
the European Geostationary Navigation Overlay Service (EGNOS) and the Multifunctional Satellite Augmentation System (MSAS) and will provide seamless air
navigation service across regional boundaries. While the ground segment consists
of eight reference stations and a master control centre, which will have sub systems
such as data communication network, SBAS correction and verification system,
operations and maintenance system, performance monitoring display and payload
simulator, Indian land uplinking stations will have dish antenna assembly. The
space segment will consist of one geo-navigation transponder.
Effective Flight Management System:
A flight-management system based on GAGAN will then be poised to save
operators time and money by managing climb, descent and engine performance
profiles. The FMS will improve the efficiency and flexibility by increasing the use
of operator-preferred trajectories. It will improve airport and airspace access in all
weather conditions, and the ability to meet the environmental and obstacle
clearance constraints. It will also enhance reliability and reduce delays by defining
more precise terminal area procedures that feature parallel routes and
environmentally optimised airspace corridors.


GAGAN will increase safety by using a three-dimensional approach
operation with course guidance to the runway, which will reduce the risk of
controlled flight into terrain i.e., an accident whereby an airworthy aircraft,
under pilot control, inadvertently flies into terrain, an obstacle, or water.
GAGAN will also offer high position accuracies over a wide geographical
area like the Indian airspace. These positions accuracies will be simultaneously
available to 80 civilian and more than 200 non-civilian airports and airfields
and will facilitate an increase in the number of airports to 500 as planned.
These position accuracies can be further enhanced with ground based
augmentation system.
REFERENCES

http://en.wikipedia.org/wiki/

http://aviationknowledge.wikidot.com/aviation:automation-in-atc

http://www.aai.aero/

http://www.allstar.fiu.edu/aero/ils.htm

http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ve
d=0CFEQFjAA&url=http%3A%2F%2Fselair.selkirk.bc.ca%2Ftraining%2Fsy
stems%2Fpowerpoint%2FAVIA%2520261%2F09INSTRUMENT%2520LANDING%2520S
YSTEM.ppt&ei=_YPrT_SLLsXPrQfP-TPBQ&usg=AFQjCNEvBXn8pGF0RKW8xaUyQJmFiYgkQQ

http://www.aai.aero/public_notices/aaisite_test/faq_cns.jsp