Training Report

Training Report | Sauradeep Paul
1
The purpose of this report is to study how communication systems play an important role in the
field of civil aviation. Since the advent of flying in manmade aircrafts in the early 1900s, there has
been a need to for the ones in the air to communicate with the people on the ground. The story
does not limit itself to communication. Since flying is not as straightforward as driving a car on
the highway, special features are required while will tell and warn flyers about their current
location, situation or anything of interest, and that too in real time. This instigated the invention
of special devices which include the DME, VOR, Radar, etc., which vastly changed the world of
flying. Flying no longer constituted of groping in the dark in case of a snow, storms, rain, fog or
the darkness. Pilots can now trust these devices which provide them with diverse information
which helps them find a suitable route and get to the ground. These devices use frequencies from
the VHF band, which are widely used in the field for the purpose of communication, navigation
and surveillance. This three make up a huge area of interest. They serve different purposes and
each of them has special equipment for the same.
We shall start with a small introduction to the Airports Authority of India along with introductions
to various units where the training was undergone. Then, we shall move on to various aspects of
communication equipment with which we were acquainted. We shall conclude the report with a
conclusion summing up all that was covered.

2
This is to certify that Sauradeep Paul, who is currently pursuing B.Tech in Electrical
Engineering at Indian Institute of Technology Ropar, has successfully completed his
summer training for his 4th
semester during the period from 9/6/2014 to 18/7/2014
at RCDU, Airports Authority of India.
Prashant Bhatt
Training Coordinator

3
1 Airports Authority of India (AAI) 4
2 Communications, Navigation and Surveillance Systems for Air Traffic
Management (CNS/ATM)
7
3 Radio Construction and Development Unit (RCDU) 9
4 Flight Inspection Unit (FIU) 10
5 Very High Frequency (VHF) 13
6 Navigational Aids (Navaids) 15
7 VHF Omnidirectional Range (VOR) 17
8 Distance Measuring Equipment (DME) 21
9 Instrument Landing System (ILS) 23
10 Non-directional Beacon (NDB) 26
11 Radar 29
12 Conclusion 32
13 Acknowledgements 33
14 References 34

4
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. During the year 2013-14, AAI handled aircraft
movement of 1536.60 Thousand [International 335.95 & Domestic 1200.65], Passengers handled
168.91 Million [International 46.62 & Domestic 122.29] and the cargo handled 2279.14 thousand
MT [International 1443.04 & Domestic 836.10].
The functions of AAI are as follows:
 Design, Development, Operation and Maintenance of international and domestic airports
and civil enclaves.
 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.
 Provision of Communication and Navigation aids, viz. ILS, DVOR, DME, Radar etc.
The main functions of AAI inter-alia include construction, modification & management of
passenger terminals, development & management of cargo terminals, development &
maintenance of apron infrastructure including runways, parallel taxiways, apron etc., Provision
of Communication, Navigation and Surveillance which includes provision of DVOR / DME, ILS, ATC
radars, visual aids etc., provision of air traffic services, provision of passenger facilities and related

5
amenities at its terminals thereby ensuring safe and secure operations of aircraft, passenger and
cargo in the country.
In tune with global approach to modernization of Air Navigation infrastructure for seamless
navigation across state and regional boundaries, AAI has been going ahead with its plans for
transition to satellite based Communication, Navigation, Surveillance and Air Traffic
Management. A number of co-operation agreements and memoranda of co-operation have been
signed with US Federal Aviation Administration, US Trade & Development Agency, European
Union, Air Services Australia and the French Government Co-operative Projects and Studies
initiated to gain from their experience. Through these activities more and more executives of AAI
are being exposed to the latest technology, modern practices & procedures being adopted to
improve the overall performance of Airports and Air Navigation Services.
Induction of latest state-of-the-art equipment, both as replacement and old equipments and also
as new facilities to improve standards of safety of airports in the air is a continuous process.
Adoptions of new and improved procedure go hand in hand with induction of new equipment.
Some of the major initiatives in this direction are introduction of Reduced Vertical Separation
Minima (RVSM) in India air space to increase airspace capacity and reduce congestion in the air;
implementation of GPS And Geo Augmented Navigation (GAGAN) jointly with ISRO which when
put to operation would be one of the four such systems in the world.
The continuing security environment has brought into focus the need for strengthening security
of vital installations. There was thus an urgent need to revamp the security at airports not only
to thwart any misadventure but also to restore confidence of traveling public in the security of
air travel as a whole, which was shaken after 9/11 tragedy. With this in view, a number of steps
were taken including deployment of CISF for airport security, CCTV surveillance system at
sensitive airports, latest and state-of-the-art X-ray baggage inspection systems, premier security
& surveillance systems. Smart Cards for access control to vital installations at airports are also
being considered to supplement the efforts of security personnel at sensitive airports.
In Airports Authority of India, the basic approach to planning of airport facilities has been adopted
to create capacity ahead of demand in our efforts. Towards implementation of this strategy, a
number of projects for extension and strengthening of runway, taxi track and aprons at different

6
airports has been taken up. Extension of runway to 7500 ft. has been taken up to support
operation for Airbus-320/Boeing 737-800 category of aircrafts at all airports.
A large pool of trained and highly skilled manpower is one of the major assets of Airports
Authority of India. Development and Technological enhancements and consequent refinement
of operating standards and procedures, new standards of safety and security and improvements
in management techniques call for continuing training to update the knowledge and skill of
officers and staff. For this purpose AAI has a number of training establishments, viz. NIAMAR in
Delhi, CATC in Allahabad, Fire Training Centres at Delhi & Kolkata for in-house training of its
engineers, Air Traffic Controllers, Rescue & Fire Fighting personnel etc. NIAMAR & CATC are
members of ICAO TRAINER programme under which they share Standard Training Packages (STP)
from a central pool for imparting training on various subjects. Both CATC & NIAMAR have also
contributed a number of STPs to the Central pool under ICAO TRAINER programme. Foreign
students have also been participating in the training programme being conducted by these
institution
Information Technology holds the key to operational and managerial efficiency, transparency and
employee productivity. AAI initiated a programme to indoctrinate IT culture among its employees
and this is most powerful tool to enhance efficiency in the organization. AAI website with domain
name www.airportsindia.org.in or www.aai.aero is a popular website giving a host of information
about the organization besides domestic and international flight information of interest to the
public in general and passengers in particular.

7
Communication, Navigation and Surveillance (CNS) are three main functions (domains) which
constitute the foundation of Air Traffic Management (ATM) infrastructure.
Communication is the exchange of voice and data information between the pilot and air traffic
controllers or flight information centers. Aircraft crews exploit communications to navigate. VHF
omnidirectional range (VOR) is an example of a legacy system to determine relative location.
The navigation element of CNS/ATM systems is meant to provide accurate, reliable and seamless
position determination capability to aircrafts. 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 on 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. Additionally, collisions with obstructions are usually fatal. Therefore, constant
awareness of position is critical for aircraft pilots.
The surveillance systems can be divided into two main types
 Dependent surveillance
 Independent surveillance
In dependent surveillance systems, aircraft position is determined on board and then transmitted
to ATC. The current voice position reporting is a dependent surveillance systems in which the
position of the aircraft is determined from on-board navigation equipment and then conveyed
by the pilot to ATC. Independent surveillance is a system which measures aircraft position from

8
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/ATM stands for Communications, Navigation and Surveillance Systems for Air Traffic
Management. The system uses various systems including satellite systems, and varying levels of
automation to achieve a seamless global Air Traffic Management system.
The Directorate General of Civil Aviation (DGCA) is the designated agency of Govt. of India under
the Ministry of Civil Aviation for making regulations, procedures and issuing directions covering
the Aeronautical Telecommunication facilities (I.e. CNS/ATM Automation facilities) . Their
instructions are to be complied with both by the Air Navigation Service Provider (ANSPs), airlines
and the airports.
Airports Authority of India (AAI) is responsible for providing CNS/ATM services in India. The
Departments of CNS acts as the nodal agency in AAI to carry out its designated functions of
looking after Aeronautical Telecommunication facilities (I.e. CNS/ATM Automation systems) in
AAI.
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)

9
The Radio Construction and Development Unit comes under CNS and deals with all the
communication devices, their installation and upkeep. The functions of RCDU are as follow.
Site selection for installation of new navigational equipment, VOR, DME, NDB & ILS.
Planning is carried out after finalizing the site. The list of works (LOW) related to civil and electrical
works for execution by station in order to construct the building and provision of electricity to
install these navigational equipment.
Executes the physical installation of equipment. A team is deputed to house the equipment in
the building and antennas, erect/dismantle masts, hoist antennas with good safety records.
The equipment are tested at site for its proper functioning. Any alignment, if required is carried
out to keep the parameters within the prescribed limits as per ICAO standards.
During the air check / calibration of the facility, all the necessary adjustments are carried out as
per the requirement of flight inspection aircraft to meet the ICAO standards.
RCDU has expertise in installation of masts / Radar scanners etc. Such activities are also made
use by other organizations viz. Indian Air Force, Indian Navy for installation of their Radars, Voice
Communication Control System (VCCS) and status indicators. They are designed and installed on
demand from various airports.

10
Flight Inspection Unit (FIU) was carved out of the Radio Development Unit of Directorate General
of Civil Aviation (DGCA), India in 1986. It is now an ISO 9001:2008 certified unit of Airports
Authority of India (AAI) since Feb'2007 (ISO 9001:2000) which carries out Flight testing of Radio
Nav. aids and associated facilities.
The Radio Development Unit of DGCA has a long history of starting flight testing in 1959 with the
help of Flight Inspection System (FIS) installed in Dakota aircraft from Allahabad, India. The Flight
Inspection system (FIS) was integrated using independent receivers, ink pen recorders, signal
generators etc. It was a fully manual system. For positional information, manual tracking of
aircraft using optical theodolites and positional event markers using VHF tones were used.
Later, FIU base was shifted to Delhi and the system was replaced by Flight Inspection system from
M/s Sierra Research Corporation, USA installed in HS-748 AVRO aircraft. This system was again
manual type but had RTT link for continuous positional information in the aircraft.
During 1986-87, the fleet of HS-748 aircrafts was replaced by Dornier DO-228 aircrafts. Sierra FIS
was also replaced with semi-automatic FIS supplied by M/s Normarc, Norway.
This started the new era of computerized system of Data collection and analysis in the field of
Flight Testing. It was possible for the system to give calculated results of required parameters
after an exercise. The system was automated using a laser based Auto-tracker for reducing the
manual error involved in the manual tracking. Bubble memory cassettes were used for Data
archival and data transfer. It was capable of carrying out flight testing of ILS Cat II.
Airports Authority of India's flight testing capability was further enhanced with the acquisition of
Fully Automatic Flight Inspection System-AFIS-200 from M/s Aerodata, Germany, in 2004. This
system uses GPS technology extensively and is capable of being used under inclement weather
condition and visibility. This is a state of the art system, fully computerized and capable of flight
testing Cat-III ILS. It is also capable of meeting flight testing requirements of modern systems like
SBAS, RNAV procedures, ADS-B etc. It is capable of flight testing of ILS using a single position for
ground equipment and in a single run it can simultaneously evaluate multiple facilities thereby
saving precious flying efforts. Independent dual receiver configuration of the system ensures very
high integrity and repeatability of the testing/calibration results.
AFIS-200 system uses P-DGPS Position reference system which works on Differential GPS
principle. It uses unique algorithm combining other sensors from the aircraft to give centimetre
level accuracy under dynamic condition. For Position Reference system, ground survey data of
the concerned facilities are required to be put in the system database. This unit has the capability

11
of carrying out the required "Ground survey" using Rascal ground survey kit with Dual frequency
GPS receivers. Additionally, fully automatic Laser Tracker is also used for giving independent and
accurate position of the aircraft while doing ILS approaches.
The AFIS-200 system is installed in two Dornier DO-228 aircrafts and one B-300 Beechcraft (Super
King Air) aircraft. The FIU team consists of qualified, proficient and experienced Flight Inspectors
headed by an Executive Director.
The 64 ILSs & 93 VORs (inclusive of both CVOR & DVOR) are Flight tested at regular intervals as
per AAI guidelines. AAI in general follows ICAO requirements in the evaluation of Flight Testing
results. Commissioning checks are carried out by FIU before operationalizing a newly installed
facility. This is followed by Periodic flight tests. The system is capable of carrying out the flight
testing of following facilities:
 ILS up to Cat-III
 VOR (CVOR/DVOR)
 DME
 NDB
 VGSI (PAPI, VASI)
 RADAR(ASR/MSSR)
 SBAS
 ADS-B
 RNAV Procedures
AAI also undertakes flight calibration/inspection of ground aids at Air force, Navy, Coast Guard
and other private Airfields in India.
Ever since inception of FIU, flight inspection of navigational aids in neighboring countries like
Vietnam, Laos, Nepal, Maldives, Bangladesh & Bhutan have been carried out on a number of
occasions under bilateral agreement.
FIU has a full-fledged ground calibration laboratory wherein various test equipment and test
benches are available for calibration of receivers, for data archival, post flight data analysis, fault
finding and maintenance activities.
 To carry out the flight inspection of Communication and Navigation surveillance facilities
at all the airports throughout the country, catering at present for 64 ILS (including CAT-
III) and 93 VORs with a fleet of Two Dornier 228 and one B-300 aircraft.
 Flight check of RADARs (SSRs, ARSRs, MSSRs) and RADAR training of ATCOs.

12
 Undertake flight inspection of Ground Navigational Aids and Visual Landing Aids at Air
Force and Naval Air Fields as well.
 Flight Inspection of DMEs, NDBs, Approach Lighting systems, and VASI / PAPI are also
undertaken.
 Has earlier undertaken Flight Inspection of Nav. Aids in the Neighboring countries like
Vietnam, Laos, Nepal, Maldives, Bangladesh and Bhutan, initially under the UNDP project,
but later on under bilateral agreements
 FIU has three fully Automatic Flight Inspection Systems, capable of undertaking flight
inspections under low visibility / bad weather conditions. Two Flight Inspection Systems
are installed in DO-228 aircrafts and one in B-300. The calibration is augmented with a
"Laser Auto Tracker" System for Cat- III ILS calibration.
 FIU is equipped with "Ground Survey Kit" for carrying out Airfield survey for position
information of Nav. Aids / Airfield.

13
Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic
waves from 30 MHz to 300 MHz, with corresponding wavelengths of one to ten meters.
Frequencies immediately below VHF are denoted high frequency (HF), and the next higher
frequencies are known as ultra-high frequency (UHF).
Common uses for VHF are FM radio broadcasting, television broadcasting, land mobile stations
(emergency, business, private use and military), long range data communication up to several
tens of kilometres with radio modems, amateur radio, and marine communications. Air traffic
control communications and air navigation systems (e.g. VOR, DME & ILS) work at distances of
100 kilometres or more to aircraft at cruising altitude.
VHF propagation characteristics are ideal for short-distance terrestrial communication, with a
range generally farther than line-of-sight from the transmitter. Unlike high frequencies (HF), the
ionosphere does not usually reflect VHF waves (called skywave propagation) so transmissions are
restricted to the local radio horizon less than 100 miles. VHF is also less affected by atmospheric
noise and interference from electrical equipment than lower frequencies. While it is blocked by
land features such as hills and mountains, it is less affected by buildings and can be received
indoors, although multipath television reception due to reflection from buildings can be a
problem in urban areas.
For analog TV, VHF transmission range is a function of transmitter power, receiver sensitivity,
and distance to the horizon, since VHF signals propagate under normal conditions as a
near line-of-sight phenomenon. The distance to the radio horizon is slightly extended over the
geometric line of sight to the horizon, as radio waves are weakly bent back toward the Earth by
the atmosphere.
An approximation to calculate the line-of-sight horizon distance (on Earth) is:
 distance in nautical miles = where is the height of the antenna in feet
 distance in kilometres = where is the height of the antenna in
metres

14
These approximations are only valid for antennas at heights that are small compared to the
radius of the Earth. They may not necessarily be accurate in mountainous areas, since the
landscape may not be transparent enough for radio waves.
In engineered communications systems, more complex calculations are required to assess the
probable coverage area of a proposed transmitter station.
Airband or Aircraft band is the name for a group of frequencies in the VHF radio spectrum
allocated to radio communication in civil aviation, sometimes also referred to as VHF. Different
sections of the band are used for radionavigational aids and air traffic control.
Listed below are the various frequency bands allocated to various communication and
navigational equipment used by the ATC and aircrafts:
Instrument Landing System 108-112 MHz, 328-336 MHz
Localiser 108-112 MHz
Glide Path 328-336 MHz
VHF Omni-directional Range 112-118 MHz
Distance Measuring Equipment 962-1213 MHz
Radar Interrogation: 1030 MHz
Reply: 1090 MHz

15
A navigational aid (also known as aid to navigation, ATON, or navaid) is any sort of marker which
aids the traveler in navigation; the term is most commonly used to refer to nautical or aviation
travel. Common types of such aids include lighthouses, buoys, fog signals, and day beacons. An
Aid to Navigation is any device external to a vessel or aircraft specifically intended to assist
navigators in determining their position or safe course, or to warn them of dangers or
obstructions to navigation.
Only the simplest airfields are designed for operations conducted under visual meteorological
conditions (VMC). These facilities operate only in daylight, and the only guidance they are
required to offer is a painted runway center line and large painted numbers indicating the
magnetic bearing of the runway.
Larger commercial airports, on the other hand, must also operate in the hours of darkness and
under instrument meteorological conditions (IMC), when horizontal visibility is 600 metres (2,000
feet) or less and the cloud base (or “decision height”) is 60 metres (200 feet) or lower. In order
to assist aircraft in approaches and takeoffs and in maneuvering on the ground, such airports are
equipped with sophisticated radio navigational aids (navaids) and visual aids in the form of
lighting and marking.
Listed below are a few navaids that aid in aircraft descent.
The VOR provides magnetic bearing information to and from the station. VOR ground stations
transmit within a VHF frequency and, thus, the signals transmitted are subject to line-of-sight
restrictions. VOR stations broadcast a VHF radio composite signal including the navigation signal,
station's identifier and voice, if so equipped. The navigation signal allows the airborne receiving
equipment to determine a bearing from the station to the aircraft (direction from the VOR station
in relation to Magnetic North).
An instrument landing system (ILS) is a radio beam transmitter that provides a direction for
approaching aircraft that tune their receiver to the ILS frequency. It provides both lateral and a
vertical signals. It 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

16
meteorological conditions (IMC), such as low ceilings or reduced visibility due to fog, rain, or
blowing snow.
Distance measuring equipment (DME) is a transponder-based radio navigation technology that
measures slant range distance by timing the propagation delay of VHF or UHF radio signals. It is
similar to secondary radar, except in reverse.
A non-directional (radio) beacon (NDB) is a radio transmitter at a known location, used as an
aviation or marine navigational aid. The signal transmitted does not include inherent directional
information, in contrast to other navigational aids. 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.
Radar is an object-detection system that uses radio waves to determine the range, altitude,
direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles,
motor vehicles, weather formations, and terrain.
These include Global Positioning System (GPS), Long Range Navigation (LORAN-C), Wide Area
Augmentation System (WAAS), Tactical Air Navigation System (TACAN) and more.

17
VHF Omni Directional Radio Range (VOR) is a type of short-range radio navigation system for
aircraft, enabling aircraft with a receiving unit to determine their position and stay on course by
receiving radio signals transmitted by a network of fixed ground radio beacons. It uses
frequencies in the very high frequency (VHF) band from 108 to 117.95 MHz.
VOR stations broadcast a VHF radio composite signal including the navigation signal, station's
identifier and voice, if so equipped. The navigation signal allows the airborne receiving
equipment to determine a bearing from the station to the aircraft.
Developed from earlier Visual-Aural Range (VAR) systems, the VOR was designed to provide 360
courses to and from the station, selectable by the pilot. Early vacuum tube transmitters with
mechanically-rotated antennas were widely installed in the 1950s, and began to be replaced with
fully solid-state units in the early 1960s. They became the major radio navigation system in the
1960s, when they took over from the older radio beacon and four-course (low/medium
frequency range) system. Some of the older range stations survived, with the four-course
directional features removed, as non-directional low or medium frequency radio beacons (NDBs)
As of 2005, due to advances in technology, many airports are replacing VOR and NDB approaches
with RNAV (GPS) approach procedures; however, receiver and data update costs are still
Figure 1: DVOR ground station, co-located with DME

18
significant enough that many small general aviation aircraft are not equipped with a GPS certified
for primary navigation or approaches.
VORs are assigned radio channels between 108.0 MHz and 118 MHz (with 50 kHz spacing); this
is in the Very High Frequency (VHF) range. The first 4 MHz is shared with the Instrument landing
system (ILS) band.
The VOR encodes azimuth (direction from the station) as the phase relationship of a reference
and a variable signal. The omni-directional signal contains a modulated continuous wave (MCW)
7 wpm Morse code station identifier, and usually contains an amplitude modulated (AM) voice
channel. The conventional 30 Hz reference signal is on a 9960 Hz frequency modulated (FM)
subcarrier. The variable amplitude modulated (AM) signal is conventionally derived from the
lighthouse-like rotation of a directional antenna array 30 times per second. Current installations
scan electronically to achieve an equivalent result with no moving parts. When the signal is
received in the aircraft, the two 30 Hz signals are detected and then compared to determine the
phase angle between them. The phase angle by which the AM signal lags the FM subcarrier signal
is equal to the direction from the station to the aircraft, in degrees from local magnetic north at
the time of installation, and is called the radial. The Magnetic Variation changes over time so the
Figure 2: VOR orientation

19
radial may be a few degrees off from the present magnetic variation. VOR stations have to be
flight inspected and the azimuth is adjusted to account for magnetic variation.
This information is then fed to one of four common types of indicators:
 An Omni-Bearing Indicator (OBI) is the typical light-airplane VOR indicator and is shown
in the accompanying illustration. It consists of a knob to rotate an "Omni Bearing Selector"
(OBS), and the OBS scale around the outside of the instrument, used to set the desired
course. A "course deviation indicator" (CDI) is centered when the aircraft is on the
selected course, or gives left/right steering commands to return to the course. An
"ambiguity" (TO-FROM) indicator shows whether following the selected course would
take the aircraft to, or away from the station.
 A Horizontal Situation Indicator (HSI) is considerably more expensive and complex than a
standard VOR indicator, but combines heading information with the navigation display in
a much more user-friendly format, approximating a simplified moving map.
 A Radio Magnetic Indicator (RMI), developed previous to the HSI, features a course arrow
superimposed on a rotating card which shows the aircraft's current heading at the top of
the dial. The "tail" of the course arrow points at the current radial from the station, and
the "head" of the arrow points at the reciprocal (180° different) course to the station.
 An Area Navigation (RNAV) system is an onboard computer, with display, and up-to-date
navigation database. At least two VOR stations, or one VOR/DME station is required, for
the computer to plot aircraft position on a moving map, or display course deviation
relative to a waypoint (virtual VOR station).
In many cases, VOR stations have co-located Distance measuring equipment (DME). A VOR co-
located only with DME is called a VOR-DME. A VOR radial with a DME distance allows a one-
station position fix.
VOR-DMEs use a standardized scheme of VOR frequency to DME channel pairing so that a specific
VOR frequency is always paired with a specific co-located DME channel.
The predictable accuracy of the VOR system is ±1.4°. However, test data indicate that 99.94% of
the time a VOR system has less than ±0.35° of error. Internal monitoring of a VOR station will
shut it down, or change-over to a Standby system if the station error exceeds some limit. A
Doppler VOR beacon will typically change-over or shutdown when the bearing accuracy exceeds
1.0°. National air space authorities may often set tighter limits. VOR beacons monitor themselves
by having one or more receiving antennas located away from the beacon. The signals from these
antennas are processed to monitor many aspects of the signals.
Doppler VOR beacons are inherently more accurate than Conventional VORs because they are
more immune to reflections from hills and buildings. The variable signal in a DVOR is the 30 Hz

20
FM signal; in a CVOR it is the 30 Hz AM signal. If the AM signal from a CVOR beacon bounces off
a building or hill, the aircraft will see a phase that appears to be at the phase centre of the main
signal and the reflected signal, and this phase centre will move as the beam rotates. In a DVOR
beacon, the variable signal, if reflected, will seem to be two FM signals of unequal strengths and
different phases. Twice per 30 Hz cycle, the instantaneous deviation of the two signals will be the
same, and the phase locked loop will get (briefly) confused. As the two instantaneous deviations
drift apart again, the phase locked loop will follow the signal with the greatest strength, which
will be the line-of-sight signal. If the phase separation of the two deviations is small, however,
the phase locked loop will become less likely to lock on to the true signal for a larger percentage
of the 30 Hz cycle (this will depend on the bandwidth of the output of the phase comparator in
the aircraft). In general, some reflections can cause minor problems, but these are usually about
an order of magnitude less than in a CVOR beacon.
It is possible that space-based navigational systems such as the Global Positioning System (GPS),
which have a lower transmitter cost per customer, will eventually replace VOR systems and many
other forms of aircraft radio navigation in use in 2008. Low VOR receiver cost is likely to extend
VOR dominance in aircraft, until space receiver cost falls to a comparable level. The VOR signal
has the advantage of weather tolerance and static mapping to local terrain. Future satellite
navigation systems and GPS augmentation systems are developing techniques to eventually
equal or exceed VOR signals.

21
Distance measuring equipment (DME) is a transponder-based
radio navigation technology that measures slant range
distance by timing the propagation delay of VHF or UHF radio
signals. DME is similar to secondary radar, except in reverse.
The system was a post-war development of the IFF
(identification friend or foe) systems of World War II.
The main purpose of the DME is to display your distance from
a VORTAC, VOR-DME, or localizer. (Some NDB stations have
collocated DME, but not many.) DME reduces pilot workload
by continuously showing your distance from the station,
accurate to within a half-mile or three percent (and usually
better). In addition, most DMEs display time-to-station and
groundspeed.
The DME system is composed of a UHF transmitter/receiver
(interrogator) in the aircraft and a UHF receiver/transmitter
(transponder) on the ground.
A typical DME transponder can provide distance information
to 100 to 200 aircraft at a time. Above this limit the
transponder avoids overload by limiting the sensitivity of the
receiver. Replies to weaker more distant interrogations are
ignored to lower the transponder load. The technical term for
overload of a DME station caused by large numbers of aircraft
is station saturation.
Combined with VOR, DME permits you to determine your
exact position from a single ground station; VOR tells you
what radial you're on and DME tells how far out on that radial
you are.
Developed in Australia, it was invented by James Gerry Gerrand under the supervision of Edward
George "Taffy" Bowen while employed as Chief of the Division of Radiophysics of the
Commonwealth Scientific and Industrial Research Organization (CSIRO). Another engineered
version of the system was deployed by Amalgamated Wireless Australasia Limited in the early
1950s operating in the 200 MHz VHF band. This Australian domestic version was referred to by
Figure 3: Distance Measuring
Equipment

22
the Federal Department of Civil Aviation as DME(D) (or DME Domestic), and the later
international version adopted by ICAO as DME(I).
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 UHF channel.
A radio signal takes approximately 12.36 microseconds to travel 1 nautical mile (1,852 m) to the
target and back—also referred to as a radar-mile. The time difference between interrogation and
reply, minus the 50 microsecond ground transponder delay, is measured by the interrogator's
timing circuitry and converted to a distance measurement (slant range), in nautical miles, then
displayed on the cockpit DME display.
The distance formula, distance = rate * time, is used by the DME receiver to calculate its distance
from the DME ground station. The rate in the calculation is the velocity of the radio pulse, which
is the speed of light (roughly 300,000,000 m/s or 186,000 mi/s). The time in the calculation is
(total time – 50µs)/2.
The accuracy of DME ground stations is 185 m (±0.1 nmi). It is important to understand that DME
provides the physical distance from the aircraft to the DME transponder. This distance is often
referred to as 'slant range' and depends trigonometrically upon both the altitude above the
transponder and the ground distance from it.
For example, an aircraft directly above the DME station at 6076 ft (1 nmi) altitude would still
show 1.0 nmi (1.9 km) on the DME readout. The aircraft is technically a mile away, just a mile
straight up. Slant range error is most pronounced at high altitudes when close to the DME station.
ICAO recommends accuracy of less than the sum of 0.25 nmi plus 1.25% of the distance
measured.
DME operation will continue and possibly expand as an alternate navigation source to space-
based navigational systems such as GPS and Galileo.

23
An instrument landing system (ILS) is a radio beam
transmitter that provides a direction for
approaching aircraft that tune their receiver to the
ILS frequency. It provides both lateral and a vertical
signals. It 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. Site selection for installation
of new navigational equipment, VOR, DME, NDB & ILS.
Tests of the ILS system began in 1929 in the United States. The Civil Aeronautics Administration
(CAA) authorized installation of the system in 1941 at six locations. The first landing of a
scheduled U.S. passenger airliner using ILS was on January 26, 1938, when a Pennsylvania Central
Airlines Boeing 247-D flew from Washington, D.C., to Pittsburgh, Pennsylvania, and landed in a
snowstorm using only the Instrument Landing System. The first fully automatic landing using ILS
occurred in March 1964 at Bedford Airport in UK.
An aircraft approaching a runway is guided by the ILS receivers in the aircraft by performing
modulation depth comparisons. Many aircraft can route signals into the autopilot to fly the
approach automatically. An ILS consists of two independent sub-systems. The localiser provides
lateral guidance; the glide slope provides vertical guidance.
Figure 4: Glide Path Station
Figure 5: Localiser Array

24
 Localiser (LOC)
A localiser is an antenna array normally located beyond the departure end of the runway and
generally consists of several pairs of directional antennas. Two signals are transmitted on one of
40 ILS channels. One is modulated at 90 Hz, the other at 150 Hz. These are transmitted from co-
located antennas. Each antenna transmits a narrow beam, one slightly to the left of the runway
center line, the other slightly to the right.
The localiser receiver on the aircraft measures
the difference in the depth of modulation (DDM)
of the 90 Hz and 150 Hz signals. The depth of
modulation for each of the modulating
frequencies is 20 percent. The difference between
the two signals varies depending on the deviation
of the approaching aircraft from the center line.
If there is a predominance of either 90 Hz or
150 Hz modulation, the aircraft is off the center
line. In the cockpit, the needle on the instrument
part of the ILS (the omni-bearing indicator (nav indicator), horizontal situation indicator (HSI),
or course deviation indicator (CDI)) shows that the aircraft needs to fly left or right to correct the
error to fly toward the centre of the runway. If the DDM is zero, the aircraft is on the LOC center
line coinciding with the physical runway center line. The pilot controls the aircraft so that the
indicator remains centered on the display (i.e., it provides lateral guidance).
 Glide slope (GS) or glide path (GP)
A glide slope station is an antenna array sited to one side of the runway touchdown zone. The GS
signal is transmitted on a carrier frequency using a technique similar to that for the localiser. The
centre of the glide slope signal is arranged to define a glide path of approximately 3° above
horizontal (ground level). The beam is 1.4° deep (0.7° below the glide-path centre and 0.7°
above).
The pilot controls the aircraft so that the glide slope indicator remains centered on the display to
ensure the aircraft is following the glide path to remain above obstructions and reach the runway
at the proper touchdown point (i.e., it provides vertical guidance).
Figure 6: ILS Components

25
Due to the complexity of ILS localiser and glide slope systems, there are some limitations.
Localiser systems are sensitive to obstructions in the signal broadcast area like large buildings or
hangars. Glide slope systems are also limited by the terrain in front of the glide slope antennas.
If terrain is sloping or uneven, reflections can create an uneven glidepath, causing unwanted
needle deflections. Additionally, since the ILS signals are pointed in one direction by the
positioning of the arrays, glide slope supports only straight-line approaches with a constant angle
of descent. Installation of an ILS can be costly because of siting criteria and the complexity of the
antenna system.
ILS critical areas and ILS sensitive areas are established to avoid hazardous reflections that would
affect the radiated signal. The location of these critical areas can prevent aircraft from using
certain taxiways leading to delays in takeoffs, increased hold times, and increased separation
between aircraft.
On some installations, marker beacons operating at a carrier frequency of 75 MHz are provided.
When the transmission from a marker beacon is received it activates an indicator on the pilot's
instrument panel and the tone of the beacon is audible to the pilot. The distance from the runway
at which this indication should be received is published in the documentation for that approach,
together with the height at which the aircraft should be if correctly established on the ILS. This
provides a check on the correct function of the glide slope. In modern ILS installations, a DME is
installed, co-located with the ILS, to augment or replace marker beacons. A DME continuously
displays the aircraft's distance to the runway.
The advent of the Global Positioning System (GPS) provides an alternative source of approach
guidance for aircraft. WAAS, EGNOS, LAAS, etc. are available in many regions to provide precision
guidance

26
A non-directional (radio) beacon (NDB) is a radio transmitter at a
known location, used as an aviation or marine navigational aid. As the
name implies, the signal transmitted does not include inherent
directional information, in contrast to other navigational aids such as
low frequency radio range, VHF omnidirectional range (VOR) and
TACAN. NDB signals follow the curvature of the Earth, so they can be
received at much greater distances at lower altitudes, a major
advantage over VOR. However, NDB signals are also affected more by
atmospheric conditions, mountainous terrain, coastal refraction and
electrical storms, particularly at long range.
NDBs typically operate in the frequency range from 190 kHz to 535 kHz (although they are
allocated frequencies from 190 to 1750 kHz) and transmit a carrier modulated by either 400 or
1020 Hz. NDBs can also be co-located with a DME in a similar installation for the ILS as the outer
marker, only in this case, they function as the inner marker. NDB owners are mostly
governmental agencies and airport authorities.
NDB radiators are vertically polarised. NDB antennas are usually too short for resonance at the
frequency they operate – typically perhaps 20m length compared to a wavelength around
1000m. Therefore they require a suitable matching network that may consist of an inductor and
a capacitor to "tune" the antenna. Vertical NDB antennas may also have a 'top hat', which is an
umbrella-like structure designed to add loading at the end and improve its radiating efficiency.
Usually a ground plane or counterpoise is connected underneath the antenna.
 Airways
A bearing is a line passing through the station that points in a specific direction, such as
270 degrees (due West). NDB bearings provide a charted, consistent method for
defining paths aircraft can fly. In this fashion, NDBs can, like VORs, define "airways" in
the sky. Aircraft follow these pre-defined routes to complete a flight plan.
Figure 7: Non-directional
Beacon

27
 Fixes
NDBs have long been used by aircraft navigators, and previously mariners, to help
obtain a fix of their geographic location on the surface of the Earth. Fixes are computed
by extending lines through known navigational reference points until they intersect. For
visual reference points, the angles of these lines can be determined by compass; the
bearings of NDB radio signals are found using radio direction finder equipment.
 Airspace Fix Diagram
Plotting fixes in this manner allow crews to determine their position. This usage is
important in situations where other navigational equipment, such as VORs with distance
measuring equipment (DME), have failed. In marine navigation, NDBs may still be useful
should GPS reception fail.
 Determining distance from an NDB station
Pilots use NDBs to determine the distance in relation to an NDB station in nautical miles.
 Instrument landing systems
NDBs are most commonly used as markers or "locators" for an instrument landing
system (ILS) approach or standard approach. NDBs may designate the starting area for
an ILS approach or a path to follow for a standard terminal arrival procedure. Marker
beacons on ILS approaches are now being phased out worldwide with DME ranges used
instead to delineate the different segments of the approach
Navigation using an automatic direction finder to track NDBs is subject to several common
effects:
 Night effect
Radio waves reflected back by the ionosphere can cause signal strength fluctuations 30
to 60 nautical miles (54 to 108 km) from the transmitter, especially just before sunrise
and just after sunset (more common on frequencies above 350 kHz)
 Terrain effect
High terrain like mountains and cliffs can reflect radio waves, giving erroneous readings;
magnetic deposits can also cause erroneous readings

28
 Electrical effect
Electrical storms, and sometimes also electrical interference (from a ground-based
source or from a source within the aircraft) can cause the ADF needle to deflect towards
the electrical source
 Shoreline effect
Low-frequency radio waves will refract or bend near a shoreline, especially if they are
close to parallel to it
 Bank effect
When the aircraft is banked, the needle reading will be offset
While pilots study these effects during initial training, trying to compensate for them in flight is
very difficult; instead, pilots generally simply choose a heading that seems to average out any
fluctuations.

29
Radar is an object-detection system that uses
radio waves to determine the range, altitude,
direction, or speed of objects. It can be used to
detect aircraft, ships, spacecraft, guided missiles,
motor vehicles, weather formations, and terrain.
The radar dish or antenna transmits pulses of
radio waves or microwaves that bounce off any
object in their path. The object returns a tiny part
of the wave's energy to a dish or antenna that is
usually located at the same site as the
transmitter. The radar sends out a signal called
the interrogation to detect objects. The signal
that comes back and is processed is called an
echo in case of a primary radar while it is called a
reply for secondary radars.
As early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected
from solid objects. In 1895, Alexander Popov, a physics instructor at the Imperial Russian Navy
School in Kronstadt, developed an apparatus using a coherer tube for detecting distant lightning
strikes. The next year, he added a spark-gap transmitter. In 1897, while testing this equipment
for communicating between two ships in the Baltic Sea, he took note of an interference beat
caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might
be used for detecting objects, but he did nothing more with this observation.
A radar system has a transmitter that emits radio waves called radar signals in predetermined
directions. When these come into contact with an object they are usually reflected or scattered
in many directions. Radar signals are reflected especially well by materials of considerable
electrical conductivity—especially by most metals, by seawater and by wet lands. Some of these
make the use of radar altimeters possible. The radar signals that are reflected back towards the
transmitter are the desirable ones that make radar work. If the object is moving either toward or
away from the transmitter, there is a slight equivalent change in the frequency of the radio
waves, caused by the Doppler Effect.
Figure 8: Radar antenna

30
Radar receivers are usually, but not always, in the same location as the transmitter. Although the
reflected radar signals captured by the receiving antenna are usually very weak, they can be
strengthened by electronic amplifiers. More sophisticated methods of signal processing are also
used in order to recover useful radar signals.
The weak absorption of radio waves by the medium through which it passes is what enables radar
sets to detect objects at relatively long ranges—ranges at which other electromagnetic
wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated.
Such weather phenomena as fog, clouds, rain, falling snow, and sleet that block visible light are
usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by
water vapor, raindrops, or atmospheric gases (especially oxygen) are avoided in designing radars,
except when their detection is intended.
Radar relies on its own transmissions rather than light from the Sun or the Moon, or from
electromagnetic waves emitted by the objects themselves, such as infrared wavelengths (heat).
This process of directing artificial radio waves towards objects is called illumination, although
radio waves are invisible to the human eye or optical cameras.
The rapid wartime development of radar had obvious applications for air traffic control (ATC) as
a means of providing continuous surveillance of air traffic disposition. Precise knowledge of the
positions of aircraft would permit a reduction in the normal procedural separation standards,
which in turn promised considerable increases in the efficiency of the airways system. This type
of radar (now called a primary radar) can detect and report the position of anything that reflects
its transmitted radio signals including, depending on its design, aircraft, birds, weather and land
features.
The range of the primary radar can be anywhere between 60-250 nautical miles. It consists of a
transponder and uses frequency in the band 1-3 GHz. This type of radar is primarily used to detect
passive targets.
Though in this case, there is no delay for the echo to rebound and come back to the source but
it need a higher power of transmission than what it would have needed to just send the signal.
This is because the echo has to come back using the power with which it initially started. Thus,
the range of the primary radar is somewhat limited. There is also a chance of detecting false
targets though this can be improved by using moving target indicators (MTI) which eliminates
targets based on their velocities.
Primary radar is still used by ATC today as a backup/complementary system to secondary radar,
although its coverage and information is more limited.

31
The need to be able to identify aircraft more easily and reliably led to another wartime radar
development, the Identification Friend or Foe (IFF) system, which had been created as a means
of positively identifying friendly aircraft from enemy. This system, which became known in civil
use as secondary surveillance radar (SSR), or in the USA as the air traffic control radar beacon
system (ATCRBS), relies on a piece of equipment aboard the aircraft known as a "transponder."
The transponder is a radio receiver and transmitter pair which receives on 1030 MHz and
transmits on 1090 MHz. The target aircraft transponder replies to signals from an interrogator
(usually, but not necessarily, a ground station co-located with a primary radar) by transmitting a
coded reply signal containing the requested information.
The secondary radar has a larger range than its primary counterpart while using the same amount
of power thus making it easier to design. It is primarily meant to be used for “friendly” targets.
Since the target itself send a reply, the reply is a bit delayed unlike in the case of primary radar.
 A transmitter that generates the radio signal with an oscillator such as a klystron or a
magnetron and controls its duration by a modulator.
 A waveguide that links the transmitter and the antenna.
 A duplexer that serves as a switch between the antenna and the transmitter or the
receiver for the signal when the antenna is used in both situations.
 A receiver. Knowing the shape of the desired received signal (a pulse), an optimal
receiver can be designed using a matched filter.
 A display processor to produce signals for human readable output devices.
 An electronic section that controls all those devices and the antenna to perform the
radar scan ordered by software.
 A link to end user devices and displays.

32
We can thus observe that all the devices listed above have had a tremendous impact on history
and continue to affect the civil aviation industry. All the equipment including DME, ILS, VOR,
Radar, NDB, etc. have a different job to fulfill. The applications, when taken as a whole, are
diverse and have helped commercial flying evolve as an industry. We also look into the future of
various equipment and learnt that, though many are being replaced by their more advanced
counterparts, many are here to stay and help in the building process of civil aviation as an
industry. Thus, we can safely conclude that considering the technology at hand in the present
and the current scenario, the equipment listed above is here to stay and will help out commuters
and the industry alike, just as it has been doing for the past decades.
On a personal level, since I am a student of a related field, the advent and progress of technology
matters quite a lot to me. Use of communication systems for aviation is one of the many diverse
applications where the technology has impacted the area significantly. It is very much possible
that I might have a future career in the same. So, getting acquainted to the subject had vastly
improved my insight on the same. This is hoping that I might get to be a pioneer in the field in
case I happen to get into it.

33
I am very grateful to Mr. Prashant Bhatt, our training coordinator, who guided us through the
training and also helped in pointing out finer points for this report. I, also, acknowledge the
people who taught us various concepts regarding the same. I am, also, grateful to the people at
RCDU and FIU who made this training experience possible. Finally, I would like to thank the
various authors of the websites which I have referred for the material in this report, the sources
of which have been listed in the next page. Altogether, it has been a very good experience and I,
personally, feel that we got to study a lot of new areas which will help or, at least, assist us further
in our respective careers.
Sauradeep Paul

34
 www.aai.aero
 www.wikipedia.org
 www.ndblist.info
 www.trevord.com
 www.avweb.com
 www.ilsapproach.com

Training Report

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Andere mochten auch

Andere mochten auch (9)

Ähnlich wie Training Report

Ähnlich wie Training Report (20)

Training Report