AAI Report
AAI Report
AAI Report
Submitted by :
Abhiroop Dutta
B.Tech (ECE), 3rd year
Tezpur University, Assam
ACKNOWLEDGEMENT
The basic aim of this training was to let the students know not only the
different elements that are required by AAI in controlling the air traffic
but also to understand the environment of the organization, the
different functions of communication and navigation equipments.
First of all, I would like to express my gratitude to my course
coordinator Sh. Santosh Kr. Gupta, Mgr(CNS) and without his help, this
project would not have been possible.
I also thank Sh. Amit Kr. Chaurasia AGM(CNS), Sh. Swaraj Chatterjee
AGM(CNS), Sh. Abhishek Keshri SM(CNS), Sh. Abhishek Kumar SM(CNS),
Sh. Hasan Ashraf SM(CNS), Sh. Pravin Kr. Singh SM(CNS), Sh. Anand
Yadav SM(CNS), Sh. Dinesh Mishra SM(CNS), Sh. Imtiaz Ahmed
SM(CNS), Sh. Iqubal Khan Mgr(CNS), Sh. Mithun Biswas Mgr(CNS), D.K.
Tiwari Mgr(CNS), Praneet Agarwal Mgr(CNS), D.B. Singh Mgr(CNS) and
Brajesh Kumar Mgr(CNS) for their support.
A special thanks to Sh. Sisir Kumar De, GM(CNS), for arranging summer
training for us.
I extend my deep sense of gratitude to Mr. Suman Bhutani, CNS Course
Administrator of CATC, Bamrauli, Allahabad for his valuable
encouragement and guidance.
CONTENTS
1. Introduction – AAI and CATC
2. Communication
2.1 Networking Fundamentals
2.2 VHF, DVR, VCCS, DATIS
2.3 AFTN, AMSS
3. Navigation
3.1 NDB
3.2 DME
3.3 DVOR
3.4 ILS
4. Surveillance
4.1 RADAR, GAGAN
5. Airport Security – XBIS, DFMD, HHMD, ETD
6. Bibliography
1. Introduction – AAI and CATC
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.
AAI manages 125 airports, which include 18 International Airport, 07
Customs Airports, 78 Domestic Airports and 26 Civil Enclaves at
Defense airfields. AAI provides air navigation services over 2.8 million
square nautical miles of air space.
The functions of AAI are as follows:
Design, Development, Operation and Maintenance of
international and domestic airports and civil enclaves.
Provision of Communication and Navigation aids, viz. ILS, DVOR,
DME, Radar etc.
Control and Management of the Indian airspace extending
beyond the territorial limits of the country, as accepted by ICAO.
Construction, Modification and Management of passenger
terminals.
Development and Management of cargo terminals at
international and domestic airports.
Provision of passenger facilities and information system at the
passenger terminals at airports.
Expansion and strengthening of operation area, viz. Runways,
Aprons, Taxiway etc.
Provision of visual aids – runway lights
Civil Aviation Training College-Allahabad
The center was established by DGCA(Directorate General of Civil
Aviation) in 1948 and now it is a part of the Airports Authority of India.
It is the pioneer institute in India which has been imparting training in
various aviation fields. It's main training areas are concerned with CNS
technology and the Air Traffic Management. This center was renamed
as Civil Aviation Training College (CATC) and it has been a member of
the ICAO TRAINAIR program which guides the aviation training
throughout the world. Ever since it's establishment it had been the
main source of production of technical personnel in the CNS and ATM
fields.
The College has two main training departments and they are further
divided in training sections. The CNS department has the
Communication and the security systems section, the navigation aids
section, the surveillance aids section and the Automation section. The
ATM department is sub divided in Aerodrome Control section, the
Approach Control section, the Terminal Area control section, Special
courses section and the Civil Airport Terminal section. Every section has
its training curriculum and conducts the courses as needed for
operations of the airports and the air navigation services. There are
other supporting sections like Meteorological section, Human
Resources, Finance, civil and electrical, Hostel management, Course
Development unit, Hospital and transport section.
Organizational structure of AAI
2. Communication –
2.1 – Networking Fundamentals
Layer 7 - Application
To further our bean dip analogy, the Application Layer is the one at the
top - it’s what most users see. In the OSI model, this is the layer that is
the “closest to the end user”. Applications that work at Layer 7 are the
ones that users interact with directly. A web browser (Google Chrome,
Firefox, Safari, etc.) or other app - Skype, Outlook, Office - are examples
of Layer 7 applications.
Layer 6 - Presentation
The Presentation Layer represents the area that is independent of data
representation at the application layer - in general, it represents the
preparation or translation of application format to network format, or
from network formatting to application format. In other words, the
layer “presents” data for the application or the network. A good
example of this is encryption and decryption of data for secure
transmission - this happens at Layer 6.
Layer 5 - Session
When two devices, computers or servers need to “speak” with one
another, a session needs to be created, and this is done at the Session
Layer. Functions at this layer involve setup, coordination (how long
should a system wait for a response, for example) and termination
between the applications at each end of the session.
Layer 4 – Transport
The Transport Layer deals with the coordination of the data transfer
between end systems and hosts. How much data to send, at what rate,
where it goes, etc. The best known example of the Transport Layer is
the Transmission Control Protocol (TCP), which is built on top of the
Internet Protocol (IP), commonly known as TCP/IP. TCP and UDP port
numbers work at Layer 4, while IP addresses work at Layer 3, the
Network Layer.
Layer 3 - Network
Here at the Network Layer is where you’ll find most of the router
functionality that most networking professionals care about and love.
In its most basic sense, this layer is responsible for packet forwarding,
including routing through different routers. You might know that your
Boston computer wants to connect to a server in California, but there
are millions of different paths to take. Routers at this layer help do this
efficiently.
Layer 2 – Data Link
The Data Link Layer provides node-to-node data transfer (between two
directly connected nodes), and also handles error correction from the
physical layer. Two sub layers exist here as well - the Media Access
Control (MAC) layer and the Logical Link Control (LLC) layer. In the
networking world, most switches operate at Layer 2.
Layer 1 - Physical
At the bottom of our OSI bean dip we have the Physical Layer, which
represents the electrical and physical representation of the system. This
can include everything from the cable type, radio frequency link (as in
an 802.11 wireless systems), as well as the layout of pins, voltages and
other physical requirements. When a networking problem occurs, many
networking pros go right to the physical layer to check that all of the
cables are properly connected and that the power plug hasn’t been
pulled from the router, switch or computer, for example.
IP Addressing
Each device connected to the internet has a unique identifier. Most
networks today, including all computers on the internet, use the TCP/IP
as a standard to communicate on the network. In the TCP/IP protocol,
this unique identifier is the IP Address. The two kinds of IP Addresses
are IPv4 and IPv6.
IPv4 vs. IPv6
IPv4 uses 32 binary bits to create a single unique address on the
network. An IPv4 address is expressed by four numbers separated by
dots. Each number is the decimal (base-10) representation for an eight-
digit binary (base-2) number, also called an octet.
IPv6 uses 128 binary bits to create a single unique address on the
network. An IPv6 address is expressed by eight groups of hexadecimal
(base-16) numbers separated by colons. Groups of numbers that
contain all zeros are often omitted to save space, leaving a colon
separator to mark the gap .
IPv6 space is much larger than the IPv4 space due the use of
hexadecimals as well as having 8 groups. Most devices use IPv4.
Static vs. Dynamic
An IP address can be either dynamic or static.
Static address is one that you configure yourself by editing your
computer’s network settings. This type of address is rare, and it can
create network issues if you use it without a good understanding of
TCP/IP.
Dynamic addresses are the most common. They’re assigned by the
Dynamic Host Configuration Protocol (DHCP), a service running on the
network. DHCP typically runs on network hardware such as routers or
dedicated DHCP servers. Dynamic IP addresses are issued using a
leasing system, meaning that the IP address is only active for a limited
time. If the lease expires, the computer will automatically request a
new lease.
IP Classes
Typically, the IPv4 space allows us to have addresses between 0.0.0.0 to
255.255.255.255. However, some numbers in that range are reserved
for specific purposes on TCP/IP networks. These reservations are
recognized by the authority on TCP/IP addressing, the Internet Assigned
Numbers Authority (IANA). Four specific reservations include the
following:
0.0.0.0 — This represents the default network, which is the abstract
concept of just being connected to a TCP/IP network.
255.255.255.255 — This address is reserved for network broadcasts, or
messages that should go to all computers on the network.
127.0.0.1 — This is called the loopback address, meaning your
computer’s way of identifying itself, whether or not it has an assigned
IP address.
169.254.0.1 to 169.254.255.254 — This is the Automatic Private IP
Addressing (APIPA) range of addresses assigned automatically when a
computer’s unsuccessful getting an address from a DHCP server.
The other IP address reservations are for subnet classes. A subnet is a
smaller network of computers connected to a larger network through a
router. The subnet can have its own address system so computers on
the same subnet can communicate quickly without sending data across
the larger network. A router on a TCP/IP network, including the
Internet, is configured to recognize one or more subnets and route
network traffic appropriately. The following are the IP addresses
reserved for subnets:
10.0.0.0 to 10.255.255.255 — This falls within the Class A address
range of 1.0.0.0 to 127.0.0.0, in which the first bit is 0.
172.16.0.0 to 172.31.255.255 — This falls within the Class B address
range of 128.0.0.0 to 191.255.0.0, in which the first two bits are 10.
192.168.0.0 to 192.168.255.255 — This falls within the Class C range of
192.0.0.0 through 223.255.255.0, in which the first three bits are 110.
Multicast (formerly called Class D) — The first four bits in the address
are 1110, with addresses ranging from 224.0.0.0 to 239.255.255.255.
Reserved for future/experimental use (formerly called Class E) —
addresses 240.0.0.0 to 254.255.255.254.
Classless Addressing
To reduce the wastage of IP addresses in a block, we use sub-netting.
What we do is that we use host id bits as net id bits of a classful IP
address. We give the IP address and define the number of bits for mask
along with it (usually followed by a ‘/’ symbol), like, 192.168.1.1/28.
Here, subnet mask is found by putting the given number of bits out of
32 as 1, like, in the given address, we need to put 28 out of 32 bits as 1
and the rest as 0, and so, the subnet mask would be 255.255.255.240.
2.2 – VHF, DVR, VCCS, DATIS
Very high frequency (VHF) is the ITU designation for the range of radio
frequency electromagnetic waves (radio waves) from 30 MHz to 300
MHz, with corresponding wavelengths of ten to one meters. Common
uses for VHF are FM radio broadcasting, television broadcasting, two
way land mobile radio systems (emergency, business, private use and
military), long range data communication up to several tens of
kilometers 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 kilometers or
more to aircraft at cruising altitude.
The VHF Unit consists of 4 parts namely –
1) VHF Transmitter/Receiver;
2) Digital Voice Recorder (DVR);
3) Voice Communication Control System (VCCS);
4) Digital Airport Terminal Information System (DATIS).
MESSAGE TEXT
NNNN
Message Categories
Via the AFTN the following message categories are submitted:
distress messages;
urgency messages;
flight safety messages;
meteorological messages;
flight regularity messages;
aeronautical information services (AIS) messages;
aeronautical administrative messages;
service messages.
Priority Indicators
Priority Indicators consist of two letters SS, DD, FF, GG and KK. They are
assigned depending on the messages category as follows:
Priority Indicator SS for Distress Messages
Priority Indicator DD for Urgency Messages
Priority Indicator FF for Flight Safety Messages
Priority Indicator GG for Meteorological Messages, Flight Regularity
Messages and Aeronautical Information Services Messages
Priority Indicator KK for Aeronautical Administrative Messages
Priority Indicator used for Service Messages are assigned as
considered appropriate by the originator, but most likely KK is used
The Priority Indicator is used to transmit AFTN messages according to
their Order of Priority. So messages with Priority Indicator SS have the
highest transmission priority. Messages with Priority Indicator DD and
FF have the second highest transmission priority and the remaining
messages with Priority Indicator GG and KK the lowest.
AMSS
The AMSS(Automatic Message Switching System) is a computer based
system, centered on the Aeronautical Fixed Telecommunication
Network (AFTN) for exchange of Aeronautical messages by means of
auto-switching for distribution of messages to its destination(s). This
system works on store and forward principle.
AMSS has four major areas:
1. System: AMSS is a dual architecture computer based system which
consists of few servers and workstations which are linked to each other
over a local area network as well as other equipment/devices for data
communication.
2. Messages: AMSS is mainly for exchange of AFTN messages, but at the
same time AMSS can handle some non-AFTN messages like AMS
messages (formally known as HFRT/Radio messages).
3.Switching: AMSS receives the messages from the terminals connected
via other switches, and after analyzing, stores the messages as well as
automatically retransmits the messages to their destination. During the
above process it uses switching system, which allows on demand basis
the connection of any combination of source and sink stations. AFTN
switching system can be classified into three major categories:
a. Line Switching b. Message Switching c. Packet Switching
4. Automation: So far as automation is considered for any system, it
could be achieved by means of mechanical devices like relay etc. and/or
application software design as per requirement. In Electronics
Corporation of India Limited (ECIL) AMSS, maximum features of
automation like message switching, analyzing, storing, periodical
statistics etc. are taken care of by AMSS software and few means of
mechanical system.
Hardware Configuration
AMSS consists of three major components:
1. Core System: It incorporates communication adapters,
protocols/suites, routing and gateway facilities. The core system is
composed of two identical computer machines (known as AMSS main
servers) which run in an operational/hot standby combination. Both
units supervise each other‘s software and hardware. In case of
software/hardware failure of the operational unit, the hot standby unit
is activated automatically so that it can take over immediately without
loss of data. The core system also includes remote communication
adaptors, multiplexers and one/two computer(s), known as
communication servers, to avail the communication gateway facilities
(if any).
2. Recording System: It has two identical mass data storage devices for
storing of all incoming and outgoing AFTN messages. It also has two
identical mirrored Database servers which are operated in parallel. The
mirroring between the two database servers is performed in the
background to store specified type messages like NOTAM, MET, ATC,
HFRT, with no effect on the regular operation.
3.2 – DME
DME(Distance Measuring Equipment), gives the slant distance between
the station and the aircraft. DME consists of two parts – DME ground
station, DME
airborne
equipment. DME
is based on rho-
theta navigation
system where
rho, the slant
distance is provided by the DME and theta, the azimuth is provided by
DVOR, which gives us the position of the aircraft.
Types of DME –
1. HPDME – High power DME (1kW), range is 200 NM, co-located
with DVOR, used for homing and enroute.
2. LPDME – Low power DME(100 W), range is 25NM, collocated with
glide path in ILS, it provides the slant distance of the aero plane
from the touchdown point in the runway.
Freq range - DME operates in the 960-1215 MHz band (UHF), critically
used band is 962-1213 MHz, 2 MHz guard band. UHF is transmission is
done through space (LOS) propagation, but LOS is restricted by radio
horizon due to curvature of earth, to overcome this we need to
increase antenna height and power.
Working of DME – DME is based on the principle of secondary radar,
i.e. the target is cooperating(active). Here the interrogator is the
aircraft and the transponder is the DME station on ground. The
interrogator enquires about its distance from the station and expects a
reply from the transponder.
How does the DME station differentiate between noise and
interrogator signal ?
The interrogator signal has two
pulses exactly set apart
12us(XDME) or 36us(YDME), and
because probability of two noise
pulses set apart exactly 12/36us is
very low, the station can
differentiate between noise and
interrogator signal.
This validation, processing of
interrogator signal and
transmitting back the reply produces a delay (Pd). To calculate the
distance of the transponder, the aircraft has a timing circuit, which
calculates the time taken (T) to get back the reply from the
transponder. Now T will also include the processing delay (Pd) time
which must be subtracted from it to compute the distance, but Pd is a
variable quantity, and there’s no way for the timing circuit in the
aircraft to know Pd, thus a fixed delay (50us –XDME, 56us-YDME), is
agreed upon, and a monitoring circuit in the transponder unit
computes the variable Pd and accordingly adds intentional delay to
make the total delay 50us or 56us, so if the aircraft is operating in
XDME it will subtract 50us from the total time, no matter what Pd is.
Practically, the speed of EM waves is far greater than the speed of
aircraft, so the aircraft is assumed to be at rest in this process. The reply
signal also has two pulses set apart 12us for XDME and 30us for YDME.
Modes of operation:
1. Search mode – When the aircraft enters the range of DME, it
begins searching for the station, in this period, rate of
interrogation (Ir) is very high, around 150 ppps (pulse pairs per
second). The station also replies with the same rate.
2. Track Mode – If in search mode, 1000 pulse pairs are sent by the
interrogator and 650 or more replies are received, i.e., reply rate
is 65% or more, then mode is changed to track mode and Ir is
reduced to 30 ppps.
Why lower Ir?
Less burden on transmitter of interrogator.
The DME station has a maximum reply rate, i.e., if 10 aircrafts
interrogating at 150 ppps, then the DME station must have a
minimum reply rate of 1500 ppps.
Squiiter
The DME transponder must have a minimum reply rate of 700
ppps(specified by ICAO) as the interrogator has an AGS circuit in the
receiver which functions only if reply rate is 700 ppps or more. So the
transponder is generating 700 ppps irrespective of whether aircrafts
are present or not, this is called squiiter pulse, otherwise receiver won’t
work. Ex – if two aircrafts A, B interrogating at 150 ppps, then each gets
a reply of 700pps which includes 150 ppps replies for aircraft A, another
150 for aircraft B and the remaining 400 ppps are squitter pulses.
How do the aircrafts distinguish between their own and other replies ?
The interrogator pulse generated by each aircraft has a unique semi
random pattern, and the transponder also generates replies for the
aircrafts in the same pattern, thus every aircraft can identify and pick
up its own signal. No two aircrafts can have the same semi random
interrogation pattern.
3.3 – DVOR
Doppler VHF Omni Range is a navigational aid which provides magnetic
bearing, i.e., the angle between the magnetic North and the line
between the receiver and the ground station. DVOR ground beacons
operate in the 108-118 MHz VHF frequency range and have a
transmission range of 300 km, use space wave propagation.
Working principle : Each VOR ground station transmits a complex
signal (in VHF
band), with
the ID of the
ground station,
a reference
signal indicating
the magnetic
North and
a directional sine
wave, changing
its phase towards
the transmitting
direction. The
second is
produced by
electronically
rotating a variable
signal. The variable signal is in phase with the reference signal when at
magnetic north, but becomes increasingly out of phase as it is rotated
to 180°. As it continues to rotate to 360° (0°), the signals become
increasingly in phase until they are in phase again at magnetic north.
The receiver in the aircraft deciphers the phase difference and
determines the aircraft’s position in degrees from the VOR ground
based unit.
Uses - DVOR located at or near an airport not only provides bearing
information for an approach to that airport, but also provides en-route
bearing information to aircraft overflying or using the airway on which
the DVOR is serving.
3.4 – ILS
ILS stands for Instrument Landing System 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.
ILS has three components – localizer, glide path, LPDME.
Transponder Reply
GAGAN
The GPS aided geo augmented navigation system (GAGAN) is a planned
implementation of a regional satellite-based 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 system over Indian airspace. The project involves
establishment of 15 Indian Reference Stations, three Indian Navigation
Land Uplink Stations, three Indian Mission Control Centers and
installation of all associated software and communication links. It will
be able to help pilots to navigate in the Indian airspace by an accuracy
of 3 m. This will be helpful for landing aircraft in tough weather and
terrain like Mangalore airport and Leh.
5.Airport Security – XBIS, DFMD, HHMD, ETD
XBIS - X-Ray Baggage Inspection System X-ray scanning procedure
works on principle of penetrating X-rays on bag or luggage to be
detected. X-ray scan distinguishes objects by their atomic number and
classifies by colour. XBIS contains following major sub assemblies: X-ray
generator, X-ray sensor amplifier PCB, Computer with software, Tunnel
with a conveyor mechanism through which the baggage passes through
Image processing software with display and keyboard.