Training Report

Training Report | Sauradeep Paul

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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.


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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


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1 Airports Authority of India (AAI) 4

2 Communications, Navigation and Surveillance Systems for Air Traffic

Management (CNS/ATM)

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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


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Airports Authority of India (AAI) was constituted by an Act of Parliament and came into being on

1st April 1995 by merging erstwhile National Airports Authority and International Airports

Authority of India. The merger brought into existence a single Organization entrusted with the

responsibility of creating, upgrading, maintaining and managing civil aviation infrastructure both

on the ground and air space in the country.

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


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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


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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.

http://www.airportsindia.org.in/public_notices/aaisite_test/main_new.jsp

http://www.aai.aero/


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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


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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)


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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.


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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


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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.


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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.


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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

http://en.wikipedia.org/wiki/Line-of-sight_propagation

http://en.wikipedia.org/wiki/Radio_horizon


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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


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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


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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.


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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


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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


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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


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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.


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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.

http://en.wikipedia.org/wiki/International_Civil_Aviation_Organization


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


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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

http://en.wikipedia.org/wiki/Antenna_(radio)

http://en.wikipedia.org/wiki/Phased_array

http://en.wikipedia.org/wiki/Amplitude_modulation

http://en.wikipedia.org/wiki/Receiver_(radio)

http://en.wikipedia.org/wiki/Difference_in_the_depth_of_modulation

http://en.wikipedia.org/wiki/Horizontal_situation_indicator

http://en.wikipedia.org/wiki/Course_deviation_indicator


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


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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


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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

http://www.aai.aero/

http://www.wikipedia.org/

http://www.ndblist.info/

http://www.trevord.com/

http://www.avweb.com/

http://www.ilsapproach.com/

Training Report

Documents

training report sauradeep

customs airports

domestic airports

summer training

air navigation services

communication systems

purpose of communication

special equipment