Internship at PCAA (Pakistan Civil Aviation Authority)

CAA PAKISTAN

High frequency (HF)

High frequency (HF) radio provides aircraft with an effective means of communication over long distance oceanic and trans-polar routes. In addition, global data communication has recently been made possible using strategically located HF data link (HFDL) ground stations. These provide access to ARINC and SITA airline networks. HF communication is thus no longer restricted to voice and is undergoing a resurgence of interest due to the need to find a means of long distance data communication that will augment existing VHF and SATCOM data links.

An aircraft HF radio system operates on spot frequencies within the HF spectrum. Unlike aircraft VHF radio, the spectrum is not divided into a large number of contiguous channels but aircraft allocations are interspersed with many other services, including short wave broadcasting, fixed point-to-point, marine and land-mobile, government and amateur services. This chapter describes the equipment used and the different modes in which it operates.

RANGE:

In the HF range (3 MHz to 30 MHz) radio waves propagate over long distances due to reflection from the ionized layers in the upper atmosphere. Due to variations in height and intensities of the ionized regions, different frequencies must be used at different times of day and night and for different paths. There is also some seasonal variation (particularly between winter and summer). Propagation may also be disturbed and enhanced during periods of intense solar activity.

The upshot of this is that HF propagation has considerable vagaries and is far less predictable than propagation at VHF. Frequencies chosen for a particular radio path are usually set roughly mid-way between the lowest usable frequency (LUF) and the maximum usable frequency (MUF). The daytime LUF is usually between 4 to 6 MHz during the day, falling rapidly after sunset to around 2 MHz The MUF is dependent on the season and sunspot cycle but is often between 8 MHz and 20 MHz Hence a typical daytime frequency for aircraft communication might be 8 MHz whilst this might be as low as 3 MHz during the night.

COMMUNICATION CHANNELS:

Frequency of operation:	VHF	117. 975 MHz  to 132.000MHz
	HF	2.500 MHz    to   30.000 MHz
Modulation:	VHF	Amplitude modulation
	HF	AM as well as SSB
SELCAL		Connected
Range:	VHF	Line of sight
	HF	Beyond line of sight

I. Air Traffic Control System:

This is a system rendered between the Air Traffic Control Institutions and the aircraft to secure the safety and the mobility of aircraft by providing ground navigation or advice, information about aircraft and the airport weather condition.

• VHF Cordless Telephone, HF Cordless Telephone
• Air Route Surveillance Radar (ARSR), Airport Surveillance Radar (ASR), Secondary Surveillance Radar (SSR)

ii. Air Control Communication System:

This is a communication system that the airline companies use for determining aircraft position to secure the navigation of their proprietary aircrafts.

• Cordless telephone by way of VHF, HF, and Inmarsat Satellite Communications
• Data Transmission by way of VHF and Inmarsat Satellite Communications

ADVANTAGE:

The HF communication system provides long range communication between:

• The Aircraft and Ground Stations.

• The Aircraft and other Aircraft.

The system operates in the 2 to 30 MHz frequency range in Amplitude Modulated or SSB mode to transmit and receive information that can be in the form of a transmitted voice or a coded digital signal. The HF system uses the skip distance phenomena to achieve long distance transmission. Skip distance transmission is most effective in the 2 to 30 MHz ranges and varies with frequency and time of day. The HF communication provides a reliable way to transmit and receive Flight Information, Landing Instruction and Voice Communication. There are two HF communication systems HF-1 and HF-2 installed in the aircraft. Each HF communication system is composed of one receiver-transmitter, an antenna coupler, lightning arrester, an antenna, a remote control unit, a microphone, a speaker or handset and necessary relays. The HF-1&2 communication systems use 115V, 400Hz, 3-phase primary power and output from 2.0000 to 29.9999 MHz or 2.8000 to 23.9999 MHz on channels spaced

at 1KHz or 100Hz.

Telecommunication

Telecommunication is a vast field. A number of key concepts reoccur throughout the literature on modern telecommunication systems. Some of these concepts are discussed below.

Basic elements

A basic telecommunication system consists of three primary units that are always present in some form:

·         A transmitter that takes information and converts it to a signal.

·         A transmission medium, also called the "physical channel" that carries the signal. An example of this is the "free space channel".

·         A receiver that takes the signal from the channel and converts it back into usable information.

For example, in a radio broadcasting station the station's large power amplifier is the transmitter; and the broadcasting antenna is the interface between the power amplifier and the "free space channel". The free space channel is the transmission medium; and the receiver's antenna is the interface between the free space channel and the receiver. Next, the radio receiver is the destination of the radio signal, and this is where it is converted from electricity to sound for people to listen to.

Sometimes, telecommunication systems are "duplex" (two-way systems) with a single box of electronics working as both a transmitter and a receiver, or a transceiver.

LAN Communication:

A local area network (LAN) is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building using network media.[1] The defining characteristics of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased telecommunication lines.

Wireless telecommunications:

Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few metres for television remote control, or as far as thousands or even millions of kilometres for deep-space radio communications.

Microwave Communication:

Microwave transmission refers to the technology of transmitting information or energy by the use of radio waves whose wavelengths are conveniently measured in small numbers of centimeter; these are called microwaves. This part of the radio spectrum ranges across frequencies of roughly 1.0 gigahertz (GHz) to 30 GHz. These correspond to wavelengths from 30 centimeters down to 1.0 cm.

The frequency bands used for digital microwave radio are recommended by the CCIR. Each recommendation clearly defines the frequency range, the number of channels that can be used within that range, the channel spacing the bit rate and the polarization possibilities.

Advantages:

   - Can cover large distances over rough terrain where you could'nt bury cables.

   - High speeds

Disadvantages:

-  Equipment very expensive

-  Relies on line-of-sight

-  Can be prone to interference

Public Address System:

A public address system (PA system) is an electronic sound amplification and distribution system with a microphone, amplifier and loudspeakers, used to allow a person to address a large public, for example for announcements of movements at large and noisy air and rail terminals.

Flight Information Display System:

A Flight Information Display system (FIDS) is a computer system used in airports to display flight information to passengers, in which a computer system controls mechanical or electronic display boards or TV screens in order to display arrivals and departures flight information in real-time. The displays are located inside or around an airport terminal. A virtual version of a FIDS can also be found on most airport websites and teletext systems. In large airports, there are different sets of FIDS for each terminal or even each major airline. FID systems are used to assist passengers during air travel and people who want to pick-up passengers after the flight.

Each line on an FIDS indicates a different flight number accompanied by:

• the airline name/logo and/or its IATA or ICAO airline designator
• the city of origin or destination, and any intermediate points
• the expected arrival or departure time and/or the updated time (reflecting any delays)
• the gate number
• the check-in counter numbers or the name of the airline handling the check-in
• the status of the flight, such as "Landed", "Delayed", "Boarding", etc.

GENERAL ELECTRONICS

General Electronics deals with the equipment that is used in general and cannot be categorized under any of the other department.

·         Digital Voice Logging System(DVLS)

·         Public Address System

Digital Voice Logging System (DVLS)

Formerly VLS was used for recording all types of conversations, works on the analog principle of magnetic tape recording. The VLS tape can record a day’s recording and has to be replaced the other day. The system is being replaced by the DVLS. It is the most important and major equipment with which GE deals. This is the Latest machine use for the recording all types of conversation. Recording stuff is reserved for 30 days in DVD-RAM. The model of  DVLS used by CAA is Marathon Evolution.

ASC M RATHON EVOLUTION

·         World’s First Linux-based communications recorder

·         Multimedia recording from, Traditional telephony and radio, VolP(Voice over IP),Trunked radio

·         Fax data, Screen data

·         The system can be configured to record, live monitor and archive communications at one location and to provide search and replay facilities locally or via LAN / WAN, Intranet or Internet.

·         Analog inputs: 4 ... 192 channels

·         Digital inputs: 4 ... 120 channels or mixed configuration of analog / digital / VoIP

·         VoIP: 4 ... 32 channels(active)

·         4 ... 120 channels(passive)

NAVIGATIONAL-AID:

Finding the way from one place to another is called NAVIGATION. Moving of an aircraft from one point to another is the most important part for any kind of mission. Plotting on the paper or on the map a course towards a specific area of the earth, in the past, used to be a task assigned to a specialized member of the aircraft's crew such a navigator. Such a task was quite complicated and not always accurate. Since, it was depended on the observation, using simple maps and geometrical instruments for calculations. Today, aerial navigation has become an art which nears to perfection. Both external Nav-aids (Navigational Aids) and on-board systems help navigate any aircraft over thousands of miles with such accuracy that could only be imagined a few decades ago.

EQUIPMENTS USED IN NAVIGATION:

·         Non-Directional Beacon:

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 Omni directional 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 used for aviation are standardized by ICAO Annex 10 which specifies that NDBs be operated on a frequency between 190 kHz and 1750 kHz although normally all NDBs in North operate between 190 kHz and 535 kHz. Each NDB is identified by a one, two, or three-letter Morse code call sign. In Canada, privately owned NDB identifiers consist of one letter and one number. North American NDBs are categorized by power output, with low power rated at less than 50 watts, medium from 50 W to 2,000 W and high being over 2,000 W.

NDB navigation consists of two parts — the automatic direction finder (or ADF) equipment on the aircraft that detects an NDB's signal, and the NDB transmitter. The ADF can also locate transmitters in the standard AM medium wave broadcast band (530 kHz to 1700 kHz at 10 kHz increments in the Americas, 531 kHz to 1602 kHz at 9 kHz increments in the rest of the world).

ADF equipment determines the direction to the NDB station relative to the aircraft. This may be displayed on a relative bearing indicator (RBI). This display looks like a compass card with a needle superimposed, except that the card is fixed with the 0 degree position corresponding to the centre line of the aircraft. In order to track toward an NDB (with no wind) the aircraft is flown so that the needle points to the 0 degree position, the aircraft will then fly directly to the NDB. Similarly, the aircraft will track directly away from the NDB if the needle is maintained on the 180 degree mark. With a crosswind, the needle must be maintained to the left or right of the 0 or 180 position by an amount corresponding to the drift due to the crosswind. (Aircraft Heading +/- ADF needle degrees off nose or tail = Bearing to or from NDB station).

·         Distance Measuring Equipment:

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.

Developed in Australia, it was invented by Edward George "Taffy" Bowen while employed as Chief of the Division of Radio physics of the Commonwealth Scientific and Industrial Research Organization (CSIRO). Another engineered version of the system was deployed by Amalgamated in the early 1950s operating in the 200 MHz VHF band. This Australian domestic version was referred to by the Federal Department of Civil Aviation as DME(D) (or DME Domestic), and the later international version adopted by ICAO as DME(I).

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. To maintain compatibility, DME is functionally identical to the distance measuring component of TACAN.

Operation:

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 low-power DME can also be co-located with an ILS glide slope antenna installation where it provides an accurate distance to touchdown function, similar to that otherwise provided by ILS Marker Beacons.

Hardware:

The DME system is composed of a UHF transmitter/receiver (interrogator) in the aircraft and a UHF receiver/transmitter (transponder) on the ground.

DME frequencies are paired to VHF Omni directional range (VOR) frequencies and a DME interrogator is designed to automatically tune to the corresponding DME frequency when the associated VOR frequency is selected. An airplane’s DME interrogator uses frequencies from 1025 to 1150 MHz DME transponders transmit on a channel in the 962 to 1213 MHz range and receive on a corresponding channel between 1025 to 1150 MHz the band is divided into 126 channels for interrogation and 126 channels for reply. The interrogation and reply frequencies always differ by 63 MHz the spacing of all channels is 1 MHz with a signal spectrum width of 100 kHz.

·         Instrument Landing System (ILS):

An instrument landing system (ILS) is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument meteorological conditions (IMC), such as low ceilings or reduced visibility due to fog, rain, or blowing snow.

Instrument approach procedure charts (or approach plates) are published for each ILS approach, providing pilots with the needed information to fly an ILS approach during instrument operations, including the radio frequencies used by the ILS components or nav-aids and the minimum visibility requirements prescribed for the specific approach.

Radio-navigation aids must keep a certain degree of accuracy (set by international standards of CAST/ICAO); to assure this is the case, flight inspection organizations periodically check critical parameters with properly equipped aircraft to calibrate and certify ILS precision

·         Localizer:

In aviation, a localizer (LOC) is one of the components of an Instrument Landing System (ILS), and it provides runway centerline guidance to aircraft. In some cases, a course projected by localizer is at an angle to the runway (usually due to obstructions around the airport). It is then called a Localizer Type Directional Aid (LDA). Localizers also exist in stand-alone instrument approach installations and are not always part of an ILS. The localizer is placed about 1,000 feet from the far end of the approached runway. It’s useful volume extends to 18 NM for the path up to 10 degrees either side of the course. For an angle of 35 degrees either side of the course the useful volume of the localizer extends up to 10 NM. Horizontal guidance gets more accurate the closer you fly to the localizer station. Localizer approaches have their specific weather minimums found on approach plates.

VHF/UHF SECTION

VHF:

·         VHF is an abbreviation for very high frequency

·         Very high  is a term used to describe the 30MHz to 300MHz portion of the radio spectrum.

·         This range of frequency will provide short range LOS(line of site)communications.

·         This range for VHF communication will typically be 2 to 20 miles depending on equipment used antenna height and terrain.

In the VHF band, electromagnetic fields are affected by the earth’s ionosphere and troposphere. Ionospheric propagation occurs regularly in the lower part of the VHF spectrum, mostly at frequencies below 70MHz. In this mode, the communication range can sometimes extend over the entire surface of the earth. The troposphere can cause Bending, ducting and scattering extending the range of communication significantly beyond the visual horizon.Auroral,meteor-scatter, and EME (earth-moon-earth, also called moonbounce)  propagation take place on occasion, but these modes do not offer reliable communication and are of interest primarily to amateur radio operators.

Uses:

Common uses for VHF  are FM radio broadcast,televisionbroadcast,land mobile stations,and long range of data communications.ICOM A110 VHF transceiver used for communications.

ICOM A110 is rugged and reliable for serious ground crew communications.

RADIO FREQUENCY BAND DESIGNATIONS:

·         30-300Hz...........ELF(extremely low frequency)

·         300-3000Hz........(voice/hearing range)

·         3-30KHz............. VLF(very low frequency)

·         30-300KHz..........LF(Low frequency)

·         300-30000KHz.....MF(Medium frequency)

·         3-30MHz.............HF(high frequency)

·         30-300MHz.........VHF(very high frequency)

·         300-3000MHz......UHF(ultra high frequency)

·         3-30GHz..............SHF(super high frequency)

·         3-300GHz............EHF(extremely high frequency)

UHF :

The UHF band goes from 300MHz to 2450MHz althrough TACS47 manpack UHF radios do not utilize frequency above 512MHz.The wavelengths associated with 300 to 512MHz range from one meters to 0.58meters.The very small antennas required for their wavelengths make them ideal for uses an high speed aircraft. Aircraft use two type

AM (Ground to air communication)

Used mostly by pilots to communicate with air traffic control

FM (Ground to ground communication).

Used primarily by mission observer to communicate with mission base

RADAR

Introduction:

Radar was secretly developed by several nations before and during World War II. The term RADAR was coined in 1941 by the United States Navy as an acronym for RAdio Detection And Ranging. The term radar has since entered English and other languages as the common noun radar, losing all capitalization. Radar is an object-detection system which 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.

Uses of Radar:

The modern uses of radar are highly diverse, including

·         Air traffic control, 

·         Radar astronomy, 

·         Air-defense systems, 

·         Antimissile systems;

·         Marine radars to locate landmarks and other ships;

·         Aircraft anti-collision systems; 

·         Ocean surveillance systems,

·         Outer space surveillance and rendezvous systems; 

·         Meteorological precipitation monitoring;

·         Altimetry and flight control systems; 

·         Guided missile target locating systems;

·         Ground-penetrating radar for geological observations.

·         High tech radar systems are associated with digital signal processing and are capable of extracting useful information from very high noise levels

RADAR Civil Aviation Authority

In aviation, aircraft are equipped with radar devices that warn of obstacles in or approaching their path and give accurate altitude readings. The first commercial device fitted to aircraft was a 1938 Bell Lab unit on some United Air Lines aircraft. Such aircraft can land in fog at airports equipped with radar-assisted ground-controlled approach systems in which the plane's flight is observed on radar screens while operators radio landing directions to the pilot.

RADAR EQUATION

The power P_r returning to the receiving antenna is given by the equation:

Where,

•         P_t = transmitter power

•         G_t = gain of the transmitting antenna

•         A_r = effective aperture (area) of the receiving antenna

•         σ = radar cross section, or scattering coefficient, of the target

•         F = pattern propagation factor

•         R_t = distance from the transmitter to the target

•         R_r = distance from the target to the receiver.

In the common case where the transmitter and the receiver are at the same location, R_t = R_r and the term R_t² R_r² can be replaced byR⁴, where R is the range.

This shows that the received power declines as the fourth power of the range, which means that the reflected power from distant targets is very small.

Principle of Working:

(Doppler’s effect)

The radar dish or antenna transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the same site as the transmitter. 

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.

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.

Transmission system of RADAR will be more clear in this block diagram,

TYPES OF RADAR

Specification of model of Radars in Karachi:

PSR Model: TA-10K

(Terminal Approach 10 cm Waveguide Klystron (Final Output Stage Power Amplifier))

(Frequency Band 2700 MHz to 2900 MHz)

Range (In Diversity Mode) = 98 NM at height of 30,000 feet

(When Both Channels are operational)

Peak Power (Per Transmitting Pulse) = 1.5 M Watts (maximum)

Peak Power (Per Transmitting Pulse) = 1.25 M Watts (Operational)

Average Power (Output) = 4 Kilo- Watts Pulse Repetition Frequency

(PRF1) = 666 Hz (Operational)

Pulse Repetition Time (PRT1) Interval = 1.5 milliseconds (Operational)

Pulse Repetition Frequency (PRF2) = 333 Hz (Option)

Pulse Repetition Time (PRT2) Interval = 3 milliseconds (Option)

Operating Frequency Range   = From 2700 MHz to 2900 MHz

Pulse Width     = 1.7 Microseconds

Antenna Rotation Speed (High) = 10 RPM

Antenna Rotation Speed (Low) = 5 RPM

Standing Wave Ratio (SWR) < 02

Range Resolution = 60 Meters (400 Nanoseconds)

Azimuth Resolution    = 1.4 Degrees

Minimum Target Area to detect = 2 Square Meters (Minimum Radar Cross-Sectional Area)

SSR Model: RSM-870

(Radar Secondary Mono Pulse)

Range (One Way)=200 NM  (1 NM = 1852Meters)

Interrogation Frequency = 1030 MHz

Reply from Transponder = 1090 MHz (This is not part of SSR Equipment)

Power Consumption (Transmitter Equip.) = 600 W a tts

Pulse Width = 0.8 Microseconds

Capacity=300 Aircrafts (Processing)

Operating band= L - Band

Transmitter output Power (High) = 1.5 K Watts

SSR Modes (Available) = Alpha (Identity) & Charlie (Altitude)

List of Test Equipments/Benches available in RCWS:

1.AFIT-1500 In Circuit digital IC Tester(Excluding RAM & EPROM ICs) up to 24 Pins Digital / TTL ICs only

2.Tracker ³Huntron=5100DSS(Hardware change Cold Tester)

3.Micro-System Trouble Shooter

4.Frequency Counter

5.Power Meter

6.Synthesizer / Level Generator

7.VHF Switch.

8.Relay Actuator

9.System Power Supply of Hewlett Packard

10.Combinational System S-645 Programmable Fault Finder of Schlumberger . (Unserviceable)

11.Curve Tracer. Tektronix-571

12.EPROM Programmer ³UnisiteS

13.TEST BENCH OF RICS TXM-4200 SYSTEM

14.Chip Master Compact(Digital IC Tester)

15.Linear Master Compact(Analogue ICs Tester)

16.Component Analyzer(Up to 3-Pins Components Tester)

17.Relative Humidity & Temperature Tester

18.ROBIN Microwave Leakage Tester

19.BK Precision Auto Ranging Capacitance Meter, Model 830A

20.BK Precision Inductance Meter, Model # 875B

21.Fluke Scope Meter, Model # 199C

22.Fluke Multimeters, Model # 187

23.Toolkit Xcelite TC-100ST

24.Soldering Station ³WellerS

25.Huntron Pro-Track-I Model 20

26.DATAMAN Universal EPROM Programmer

27.De-Soldering Station ³WellerS

28.Huntron Scanner-I(part of Tracker)

29.Agilent Digital Color LCD Oscilloscope

30.6-GHz Spectrum Analyzer Model FSL6

31.Battery Load Tester (200A)

32.ERSA Infra-Red Rework Station IR/PL-550A

Visit to Radar, ECR, ATCR etc

In Radar’s visit we have seen the radar equipment and its function which we have taught in RCWS in EED. We also had a chance to see the working radar so that we have gained more knowledge. And then we went to air traffic control room where we experienced the live air traffic control by the skilled controllers of CAA.

Control tower’s visit was one of the best part of the visit. Here we experienced the controlling of aircrafts on ground and some nautical miles in the air. The primary method of controlling the immediate airport environment is visual observation from the aerodrome control tower (TWR). The TWR is a tall, windowed structure located on the airport grounds. Aerodrome or Tower controllers are responsible for the separation and efficient movement of aircraft and vehicles operating on the taxiways and runways of the airport itself, and aircraft in the air near the airport, generally 5 to 10 nautical miles (9 to 18 km) depending on the airport procedures.

Radar displays are also available to controllers at some airports. Controllers may use a radar system called Secondary Surveillance Radar for airborne traffic approaching and departing. These displays include a map of the area, the position of various aircraft, and data tags that include aircraft identification, speed, altitude, and other information described in local procedures. In adverse weather conditions the tower controllers may also use Surface Movement Radar (SMR), Surface Movement Guidance and Control Systems (SMGCS) or Advanced SMGCS to control traffic on the manoeuvring area (taxiways and runways).

Equipment Control room was also a great experience for us. Here different transceivers are placed. There are also different equipment includes VOR display, DME display, Voice recording system and transponder for making the air travel more secure and effective. These equipments were taught by the instructors in EED before the visit so that we can easily understand their working.