Basic Avionics Presentation

AIR SPEED INDICATOR ALTIMETER

HORIZONTALSITUATION INDICATOR

ALL AIRCRAFT MUST HAVE CERTAIN INSTRUMENTS IN A SPECIFIC POSITION. THIS IS CALLED THE BASIC T.

ARTIFICIALHORIZON

AIR SPEED INDICATOR

ATTITUDE & DIRECTIONINDICATOR ALTIMETER


ALL AIRCRAFT MUST HAVE CERTAIN INSTRUMENTS IN A SPECIFIC POSITION. THIS IS CALLED THE BASIC T.

THE NAVIGATION SYSTEM GIVES NAVIGATION DATA ON RELATED INDICATORS ON THE INSTRUMENT PANEL. THERE ARE FIVE DIFFERENT TYPES OF NAVIGATION SYSTEMS INSTALLED. THESE SYSTEMS ARE:-

FLIGHT ENVIRONMENT DATA

ATTITUDE AND DIRECTION

LANDING AND TAXI AIDS

INDEPENDENT POSITION DETERMINING

DEPENDENT POSITION DETERMINING

NAVIGATION SYSTEMS

FLIGHT ENVIRNOMENT DATAPITOT/STATIC SYSTEM

AIR SPEED INDICATOR

ALTIMETER

VERTICAL SPEED INDICATOR

ATTITUDE & DIRECTION

HORIZONTAL SITUATION INDICATOR

TURN & SLIP

RADIO MAGNETIC INDICATOR

ATTITUDE & DIRECTION INDICATOR

STANDBY COMPASS

LANDING & TAXI AIDS

A O M

INSTRUMENT LANDING SYSTEM (ILS)

GLIDESLOPE & LOCALISER

HORIZONTAL

SITUATION INDICATOR

MARKER BEACON


INDEPENDENT POSITION DETERMNING

WEATHER RADAR

RADAR ALTIMETER

GROUND PROXIMITY WARNING

TCAS

DEPENDENT POSITION DETERMININGRADIO

MAGNETIC INDICATOR

VOR

Distance Measuring Equipment

TRANSPONDER

ADF

FLIGHT ENVIRNOMENT DATAPITOT/STATIC SYSTEM

FLIGHT ENVIRNOMENT DATA

This dimensional change is measured by a rocking shaft and a set of gears that drives a pointer across the instrument dial.

An Airspeed Indicator is a differential pressure gauge that measures the dynamic pressure of the air through which the aircraft is flying.

Dynamic pressure is the difference in the ambient static air pressure and the ram pressure caused by the motion of the aircraft through the air.

FLIGHT ENVIRNOMENT DATAALTIMETER.

• GIVES A BAROMETRIC HEIGHT.• THIS IS ACHIEVED BY HAVING A STATIC

SOURCE ACTING ON A BELLOWS.• AS THE AIRCRAFT CLIMBS, THE STATIC

PRESSURE IN THE INSTRUMENT DECREASES, THE BELLOWS EXPANDS, AND THE NEEDLE INDICATES A HIGHER ALTITUDE.

• AS THE AIRCRAFT DESCENDS, THE STATIC PRESSURE IN THE INSTRUMENT INCREASES, THE BELLOWS CONTRACTS, AND THE NEEDLE INDICATES A LOWER ALTITUDE.

• TO COUNTER DAILY CHANGES IN PRESSURE, IT IS POSSIBLE TO ADJUST THE BAROMETRIC PRESSURE. A STANDARD DAY IS 1013 MILLIBARS.

FLIGHT ENVIRNOMENT DATAVERTICAL SPEED INDICATOR.

• THE VERTICAL SPEED INDICATOR USES THE CHANGE IN STATIC PRESSURE TO GIVE A RATE OF CLIMB OR DESCENT.

• THIS IS ACHIEVED BY HAVING A CALIBRATED LEAK.

• BY ALLOWING THE STATIC PRESSURE TO LEAK FROM THE INSTRUMENT AS IT CLIMBS INDICATES A RATE OF CLIMB.

• BY ALLOWING THE STATIC PRESSURE TO LEAK INTO THE INSTRUMENT AS IT DESCENDS INDICATES A RATE OF DESCENT.

AIRCRAFT COMPASS SYSTEM

STANDBY COMPASS

&

GYRO COMPASS


ATTITUDE AND DIRECTIONSTANDBY COMPASS.

• The standby or E2B compass is a direct indicating compass system.

• This is normally a magnetic compass suspended in oil to damp out any overswing.

• It can be corrected for A errors (errors induced by the aircraft’s magnetic field) by rotating the whole assembly on its mounting.

• B & C errors (earth’s magnetic field) can be removed by making adjustments to the B & C correction pots.

• It is highly susceptible to local magnetic fields and is only reliable when these fields are in the same state as they were when the compass swing was carried out (i.e.. the heated windows being switched off).

ATTITUDE AND DIRECTIONCOMPASS SYSTEM


FLUX VALVE.

This consists of a 3 spoke device on a flexible mounting, damped with oil. It is secured to the aircraft as far from magnetic interference as possible.

• A coil mounted on the hub of the spokes is fed with 400 Hz a.c. Coils mounted on each spoke are connected so that normally the EMF’s induced in them add up to zero. However the earth’s magnetic field causes an imbalance in this, giving an output proportional to the direction of the earth’s magnetic field.

• A errors (aircraft magnetic field errors) are normally removed by rotating the flux valve.


VERTICAL GYRO.

• If a Vertical Gyro is used as a heading indicator, it will have the normal problems of a gyroscope used over the earth’s surface.

• It could drift a maximum of 360 degrees in 24 hours and would normally be corrected by reference to a compass.

• Normally, the directional gyro unit contains the electronics required to update and correct the output signal.


COMPASS COMPENSATOR.

• This allows the compass system to be corrected for B & C errors (earth’s magnetic field)


The Horizontal Situation Indicator (HSI), has a rotating compass card which indicates the aircraft heading relative to the aircraft’s nose.

The HSI compass card is driven by the output from the vertical gyro.

The Radio Magnetic Indicator (RMI), compass card is also driven by the output from the vertical gyro.

NOTE: No. 1 HSI and No. 2 RMI are driven by the No. 1 compass system and vertical gyro.

No. 2 HSI and No. 1 RMI are driven by the No. 2 compass system and vertical gyro.


RADIOMAGNETICINDICATOR



• The Attitude & Direction indicator, displays a constant visual indication of the aircrafts lateral and longitudinal attitude relative to the horizon.

• The pilots and co-pilots indicators are powered with 115-volt Ac, 400 Hz through 0.5 ampere fuses labelled “PILOT ART HORIZ” and “COPILOT ART HORIZ”, located on the overhead fuse panel.

• A symbolic aircraft reference bar in the centre of the instrument represents the aircraft.

ATTITUDE AND DIRECTIONSTANDBY HORIZON.

• A Dc-powered standby indicator was installed on the pilots left panel to fulfil European Union requirements for all series aircraft.

• Power for the unit is obtained from the Auxiliary battery bus-bar through a 5 ampere circuit breaker labelled “STANDBY ART HORIZ” LOCATED ON THE MAIN CIRCUIT BREAKER PANEL.

ATTITUDE AND DIRECTIONTURN & SLIP INDICATOR.

• The turn and slip indicator consists of an electrically driven gyroscope which indicates rate of yawl, and a fluid dampened, ball type inclinometer which indicates slip and skid.

• Each instrument has a power off warning flag.


GENERAL.

• The instrument landing system (ILS) is a radio navigation system used when the aircraft is in approach mode.

• ILS is used to provide steering information to keep the aircraft approach to a runway. It places the aircraft in proper course and altitude for a landing.

INSTRUMENT LANDING SYSTEM.

An ILS facility provides guidance to an aircraft by providing signals that direct the pilot to a 3 degree approach angle centred along the runway. This is done by separating the approach into horizontal and vertical components. Deviation from the localiser course (left/right) would be displayed on an indicator, as would deviation from the glideslope (up/down).

Marker beacons are installed along the glidepath as reference points for locating the aircraft along the glidepath and as reference points for aircraft flying at higher altitudes.

Localiser and glideslope frequencies are paired, selection of the localiser frequency automatically selects that of the glideslope.



C O N TR O L U N IT IL S IN D IC A TO R R E C E IV E R A N TE N N A A IR C R A F TC O M M S

IL SA IR C R A F T S Y S TE M

LANDING AND TAXI AIDSCONTROL UNIT.

• The control unit provides the necessary control and switching circuits for the ILS system.

• The control unit may also provide frequency selection for VHF comms

• The control unit selects the VHF localiser frequency which automatically selects the paired UHF glideslope frequency.

LANDING AND TAXI AIDSDEVIATION INDICATORS.

• The ILS signals will produce steering signals to indicate how much the aircraft is off track either up/down or left/right.

• If the signal is unreliable a flag will cover the indicators or a warning flag will be displayed on the indicator


RECEIVER• The receiver contains the necessary circuits

for receiving, decoding and processing the bearing information from the transmitted VOR signal.

• The receiver also contains self monitoring circuits that confirm the validity of the received signals and the reliability of the bearing information sent to the indicator.

• Most VOR receivers also contain circuits required to decode and process lateral and/or vertical guidance information from an ILS ground facility.

• It may also process DME and marker beacon information.


ANTENNA• Three antennas are required for

complete ILS operation.

• A horizontally polarised, omnidirectional antenna operating in the 108 to 112 Mhz range is required for localiser operation. Typically the localiser receiver uses the same antenna as the VOR.

• Glideslope operation requires a folded dipole antenna capable of receiving AM signals in the 329 to 335 Mhz range.

• The marker beacon typically uses a loop antenna operating at 75 Mhz.

LANDING AND TAXI AIDSCOMMS SELECTOR• The ground station sends out an audio signal (morse code) every 30

seconds.

• This identifying signal is sent through the aircraft comms system to allow the crew to identify the VOR/ILS beacon that they are tracking.

• Audio signals are sent to the aircraft system as it flies over the marker beacons :- 400 Hz outer, 1300 Hz middle and 3000 Hz airways tones.

A O M

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1 COM 2 3 COM 4 1 NAV 2 MKR 1 ADF 2DME


L O C A L IS E RA N TE N N A

G L ID E S L O P EA N TE N N A

M A R K E R B E A C O NA N TE N N A S

IL SG R O U N D S TA TIO N S


LOCALIZER.

• This is located at the far (departure) end of the instrument runway.

• It operates between 108 and 112 Mhz• Its lowest assigned frequency is 108.1

Mhz.• Only the odd decimal frequencies are

localiser frequencies, i.e. 109.3, 110.7 and 111.9.

• The localiser is radiated to produce two intersecting lobes, left and right, directed along the length of the runway. The lobe on the left is predominately modulated with 90 Hz and the lobe on the right with 150 Hz. The two signals are equal along the centre line of the runway.

LANDING AND TAXI AIDSGLIDESLOPE.

• This is located at the near end of the runway to one side.

• It operates between 328.6 and 335.4 Mhz.

• The correct frequency is automatically selected on selecting the localiser frequency.

• The glideslope signal is radiated to produce two intersecting lobes one above the other. The upper lobe is predominantly modulated at 90 Hz and the lower at 150 Hz, with the two signals being equal along the glidepath.

LANDING AND TAXI AIDSMARKER BEACON.• There are three marker beacon antennas,

outer, middle, inner.

• The outer marker transmits a 400Hz audio tone and when over it, illuminates the blue outer marker light, typically 4 to 7 miles from the runway.

• The middle marker transmits a 1300Hz audio tone and when over it, illuminates the amber middle marker light, typically 0.6 miles from runway.

• The airways marker transmits a 3000Hz audio tone and when over it, illuminates the white inner light, typically at the end of the runway.

A O M


HOW ILS WORKS.

• The pilot selects the frequency of an ILS ground station.

• The matched glideslope frequency is automatically selected.

• The pilot using conventional navigation techniques or guidance from air traffic control, will then manoeuvre the aircraft onto the approach course.

• Once on the approach course, the aircraft will cross the marker beacons as it descends.

• The aircraft, now within range of the runway and on direct course for it, is flown to a landing.


HOW ILS WORKS.

• If the aircraft is too far left then the proportion of the 90 Hz signal is greater than that of the 150 Hz and a fly right signal is displayed on the localiser steering indicator. The converse of this happens if the aircraft is too far right.

• If the aircraft is too far up then the proportion of the 90 Hz signal is greater than that of the 150 Hz and a fly down signal is displayed on the glideslope steering indicator. The converse of this happens if the aircraft is too low.

• If all signals are in equilibrium, then the aircraft is flying right down the middle of the ILS signals.

RADAR ALTIMETER

RAD ALT



GENERAL.

The radar altimeter is used to provide accurate aircraft

height above terrain information.

This is an airborne system used to determine the accurate aircraft height above terrain.

The altimeter transmits a constant train of radar frequency pulses to the ground, receives the reflected pulses, and measures the elapsed time between the transmission and reception of each pulse. The elapsed time is processed to provide an analogue voltage to drive the indicator.

INDEPENDENT POSITION DETERMINIG

TR A N S M ITTE R /R E C E IV E R

IN D IC A TO R A N TE N N A

R A D A RA L TIM E TE R


TRANSMITTER/RECEIVER.

• The transmitter/receiver unit contains all the necessary circuitry for the generation, reception and tracking of height determining radar frequency pulses.

INDEPENDENT POSITION DETERMININGINDICATOR.

• The indicator converts the output of the transmitter/receiver unit, to a direct scale readings of the aircrafts height above terrain.

• On pushing the test button, the alt needle is driven to 50 feet, the on/off/failure flag comes into view and the low level warning light comes on if the low level warning system is set to less than 50 feet.

• And a low level height warning system:- This consists of an adjustable bug and an indicator light or lights.


ANTENNA.

• Two identical horn type antennas are flush mounted to the underside of the aircraft.

• They are connected to the transmitter/receiver by co-axial cables (the length of which is critical).

• One antenna is used for transmitting and the other for receiving.

• Bonding of the antenna to the aircraft skin is critical and poor bonding can lead to erratic readings.


HOW RAD ALT WORKS.

• The transmitter produces a train of radar frequency pulses to drive the transmitter antenna.

• Coincident with the transmission of each pulse a reference pulse is supplied from the transmitter to the tracker.

• The receiver receives the reply pulses from the receive antenna, processes them and sends them to the tracker.

• The tracker takes the reference pulse and the received pulse measures the time difference and converts this to an analogue voltage to drive the indicator.

• The indicator takes the voltage and drives the needle to show aircraft height. If the aircraft is above the radar altitude range, the needle is driven behind the no track mask.

TRAFFIC ALERT AND COLLISION AVOIDANCE SYSTEM

TCAS

&

ACAS


INDEPENDENT POSITION DETEMINING

GENERAL.

• Traffic alert and collision avoidance system (TCAS) and Airborne collision and avoidance system (ACAS) provide conflict resolution advisories in the form of vertical readouts.

• It can be operated in several configurations to display traffic and resolution advisories.


TCAS/ACAS

This is a ground and airborne based system using the mode S facility of the ATC. Mode S transponder equipped aircraft aircraft and ground station enhance the operation of the ATC by adding a data link feature and a discrete interrogation capability, in addition to performance improvements in determining the aircraft location.

The mode S transponder data link capabilities include bi-directional air-to-air information exchange, ground to air data uplink, air to ground data downlink and multisite message protocol.


M O D E SA TC TR A N S P O N D E R

TC A SC O M P U TE R

TC A SA N TE N N A

D IS P L A YU N IT

TC A SA IR C R A F T S Y S TE M


MODE S ATC TRANSPONDER.

• As a Mode S transponder equipped aircraft receives an ATC Mode S interrogation, it sends out a reply signal that can be received by both ATC and other Mode S transponder systems.

• As a mode S aircraft flies into the airspace served by another mode S interrogator, the first mode S interrogator may send position information and the aircraft’s discreet address to the second interrogator.

• Aircraft are tracked by the interrogator throughout its assigned airspace.

• A mode S aircraft replies with its altitude or its ATC code,depending on the interrogation.


TCAS COMPUTER.

• The transmitter interrogates mode C and mode S transponders in nearby aircraft. The receiver (in the computer) accepts transponder replies.

• The computer determines the closest point approach (the minimum separation between the TCAS equipped aircraft and the traffic encountered.

• The computer then gives traffic alert (TA) and resolution advisories (RA) as appropriate on the TCAS display.

• It also generates the appropriate audio response.


TCAS ANTENNA.

• The TCAS antennas mount on the top and bottom of the aircraft to give all round aircraft cover.


DISPLAY UNIT.

• The traffic display shows nearby traffic with mode C or mode S transponders that reply to TCAS interrogations.

• The traffic display shows an airplane symbol in white in the lower centre of the screen.

• A white dotted 2nmi range ring around the airplane symbol (units can show a 40nmi range and a 20nmi dotted circle appears when 40nmi is selected).

• Four types of TCAS traffic symbols. RA traffic- solid red square. TA traffic- solid amber circle. Proximate traffic- solid white or cyan circle. Other traffic as open white or cyan diamond

• Various TCAS annunciators and flags

INDEPENDENT POSITION DETERMININGHOW TCAS WORKS.• TCAS is designed to protect a volume of

airspace around the TCAS equipped aircraft. The system interrogates mode C & S transponders in nearby aircraft and the computer analyses their replies to show the aircrafts’ bearing, range, altitude and vertical speed on a traffic display.

• The computer also analyses the replies to determine a straight line closure rate and the closest point of approach (CPA) between your aircraft and the traffic aircraft.

• When the closest point of approach (CPA) penetrates the protected airspace around your aircraft and the is within 15 to 48 seconds , the system gives appropriate aural and visual TA & RA on the TCAS display.


HOW TCAS WORKS.

• The TCAS system gives RA’s in the form of vertical manoeuvre designed to increase the separation of the intruding threat aircraft and your own.

• The vertical manoeuvres are shown as red and green arcs on the VSI indicator along the vertical speed scale.

• The green arc shows the vertical speed to fly and the red arc shows the vertical speed to avoid.

INDEPENDENT POSITION DETERMININGEGPWS.

The EGPWS uses the GPWS functions plus additional enhanced terrain alerting features.

The EGPWS provides terrain display, situational awareness, terrain alerting and warning, and obstacle alerting and warning to the pilot.

It is intended to give advanced alerting and warning to the pilot to help reduce the possibility of controlled flight into terrain.

The EGPWS triggers the following warnings:-Aural warnings comprising aural messages heard over the flight compartment headsets and speakers.Visual warnings: illumination of TERRAIN and BELOW G/S (below glideslope) lamps in the pilots and co-pilots field of vision.

Visual warnings on a display using colours to represent the threat.

EGPWS


A IR C R A F TA U D IO

W A R N IN GL A M P S

E G P W SC O M P U TE R

D IS P L A Y

E G P W SA IR C R A F T S Y S TE M


AIRCRAFT AUDIO.

• The aural messages are digitally synthesized and stored in read only memories in the GPWS computer.

• When a warning is generated, the information stored in the appropriate memory location is retrieved and converted to two audio signals. One is applied to the pilots headset and speaker, the other to the co-pilots headset and speaker.

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WARNING LAMPS.

• The visual warning of a EGPWS mode come in the form of a lamps in direct view of the pilot and co-pilot.


EGPWS COMPUTER.

• This contain the necessary circuits to receive data from various sources, process it and produce the appropriate warnings to the aircrew.

• It also produces a visual warning onto a display.

• Inputs to the EGPWS computer come from the:-– Rad ALT– Air Data and Servo Instrument

System– Landing and Taxing Aids– Flight Instrument System– Flap Control– Landing Gear– Stall Warning


DISPLAY.

• This displays terrain threats, by the use of colours, on the aircraft flight path.

• The display range is selectable by the pilot from 1 nm to 320 nm.

• The colours are:-

– 50% Red :- +2000 feet and over– 50% Yellow :- +1000 feet to +2000 feet– 25% Yellow :- -250 feet to +1000 feet– 50% Green :- -1000 feet to –250 feet– 16% green :- -2000 feet to –1000 feet– Black :- below –2000 feet– Cyan :- below –2000 feet


HOW EGPWS WORKSThe EGPWS receives the following inputs– Radio height from the radar alt.– Vertical speed from the air data system.– Indicated air speed from the air data system.– Glideslope deviation and validity from the VOR/ILS/MB system.– A back course localiser signal if back course mode is selected.– A signal from the flaps, if the flaps are in the landing position. – A signal from the landing gear, if retraceable landing gear is fitted.– An input from the stall warning if triggered.

The EGPWS computer processes these inputs and determines which of the 6 warning modes are enabled and if any of the warning envelopes are being penetrated.

When the aircraft operation deviates into a dangerous condition (warning envelope penetrated) visual and aural warnings are generated.


MODE VISUAL WARNING AURAL WARNING

1- Excessive sink rate TERRAIN lamps SINK RATE

WHOOP WHOOP PULL UP

2- Excessive closure rate TERRAIN lamps TERRAIN

WHOOP WHOOP PULL UP

3- Altitude loss after takeoff TERRAIN lamps DON’T SINK

4- Terrain clearance TERRAIN lamps TOO LOW TERRAIN

TOO LOW GEAR

TOO LOW FLAPS

5- Inadvertent descent below glideslope

BELOW G/S INHIBIT LAMPS GLIDESLOPE

6- Advisory callouts BANK ANGLES

MINIMUMS


HOW EGPWS WORKS.

• The EGPWS computer processes the data from its memory, using the information from its inputs work out where it is, and produce a terrain map of the aircrafts locale.


MODE 1


MODE 2A


MODE 2B


MODE 3


MODE 4A


MODE 4B


MODE 4C


MODE 5


EGPWS INDICATORS


WEATHER RADAR


WEATHER RADAR The weather radar system is an airborne system that

provides a moving navigational display which graphically shows the relationship of the pilots selected course to significant weather.

Only precipitation (or objects more dense than water) will be detected by X –band weather radar. Therefore weather radar does not detect clouds, thunderstorms or turbulence directly.

The best radar reflectors are raindrops and wet hail. The larger the raindrop the better it reflects. Because large raindrops in a concentrated area are a characteristic of a severe thunderstorm, the radar displays this as a strong echo.


D IS P L A YU N IT

TR A N S M ITTE R /R E C E IV E R

A N TE N N A

W E A TH E RR A D A R


DISPLAY UNIT

• The basic weather display allows the selection of various modes of operation.

• Various ranges.• And by the use of colours a weather

intensity indication.• Black :- nil returns.• Green :- weak returns, light turbulence.• Yellow :- moderate returns, light to

moderate turbulence.• Red :- strong/very strong returns,

severe turbulence.• Magenta :- intense/extreme,

severe/extensive turbulence, hail lightning.


TRANSMITTER/RECEIVER

• This contains all the necessary electronics to generate the transmission pulses and receive and decode the replies.

• It also controls the motors that control the sweep of the antenna.

• The decode replies are transmitted to the display unit, and depending on the mode selected displayed as weather returns.

• This unit can be part of the antenna unit to limit the use of wave guides.


ANTENNA

• Mounted in the nose cone of the aircraft.

• It is a single antenna that transmits and receives the X-band (8000 to 12500 MHz) radio pulses.


HOW WEATHER RADAR WORKS

The transmitter generates microwave energy in the form of pulses. These pulses are then transferred to the antenna where they are focused into a beam by the antenna. When a pulse intercepts a target, the energy is reflected as an echo, or return signal back to the antenna. From the antenna, the return signal is transferred to the receiver and processing circuits located in the Tx/Rx unit. The echo’s or return signals are displayed on a indicator.


AUTOMATIC DIRECTION FINDER

ADF


INTRODUCTION

• The automatic direction finder (ADF) is the oldest and most widely used radio navigation systems because of the availability of numerous ground stations.

INTODUCTIONThe concept of ADF navigation is based on the ability of an airborne system to provide bearing indication with respect to the aircraft’s centre line, based upon the direction of arrival of a radio wave from a selected ground station.

I

The airborne portion of the ADF consists of a receiver, control unit, indicator, fixed loop antennas and a sense antenna.

The ground facility consists of a transmitter and antenna. A typical ground facility would be an AM radio station (1215 KHz Virgin) or a non-directional beacon (NDB).



A IR C R A F TA U D IO

IN D IC A TO R C O N TR O L U N IT R E C E IV E R A N TE N N A

A D FA IR C R A F T S Y S TE M


AUDIO SYSTEM• On selecting an ADF beacon frequency the

beacon identification can be confirmed either through the aircraft headset or speaker, depending on audio control unit selection, by its morse ident or audio output.

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DEPENDENT POSITION DETERMININGINDICATOR

• All indicators used with the ADF system indicate the bearing of the ground station. That is , the needle of the indicator always points to the station that the receiver is tuned to.

• An ADF indicator will have a needle rotating against a rotating azimuth card, to indicate the bearing to a ground station, relative to the nose of the aircraft. (Radio Magnetic Indicator, RMI)

• If the ADF signal is lost or ANT is selected on the control unit, the receiver will send the indicator an invalid signal which will park the ADF indicating needle at the 3 ‘o’ clock position.

DEPENDENT POSITION DETERMININGCONTROL UNIT• The ADF control unit provides the

control and switching circuits to select the ADF receiver operating mode and frequency.

• It allows selections in the ADF operating range between 190 to 1750 KHz.

• With the switch position in the ANT position, audio only signals are processed by the receiver. The bearing pointer will park at the 3 ‘o’clock position.

• With the switch position in the ADF position, both audio and bearing information is processed by the receiver.


RECEIVER

• The ADF receiver contains the necessary circuits for the reception and processing of radio signals to provide relative bearing information to an indicator.

• The receiver also contains the circuits required to confirm the validity of the received signal and the reliability of the receiver itself.

• If the received signal is not valid or if no signal is received, then it sends an output signal to the indicator telling it to park the ADF needle at the 3 ‘o’clock position.

DEPENDENT POSITION DETERMININGANTENNA

• The ADF receiver requires two types of antenna. An omnidirectional sense antenna is required to help tune the receiver and a loop antenna is required to provide the bearing. Both antennas operate in the 190 to 1750 KHz frequency range.

• Characteristics of the loop antenna are used to determine the bearing to a selected ground station. Since the loop antenna is directional, the received signal strength is relative to the position of the antenna with respect to the ground station.

• In the current ADF systems, the antennas are mounted in a fixed position relative to the aircraft. Two loop antennas are used and are physically 90 degrees apart. The sense antenna may also be contained in the same package as the loop antennas.


C O M M E R C IA LR A D IO S TA TIO N5 5 0 TO 1 6 6 0 K h z

N O N D IR E C TIO N A L B E A C O N SN D B

1 9 0 TO 5 5 0 K h z

A D FG R O U N D S TA TIO N S

1 9 0 TO 1 7 5 0 K h z


COMMERCIAL RADIO STATIONS

• In some parts of the world, commercial radio stations may be the only navigational aid available. They often give a valuable cross-check on other navigation facilities.

• Commercial broadcast stations are not limited to line of sight reception. ADF systems can receive signals from over the horizon.

• Ground waves are the only transmitted waves suitable for direction finding with loop antennas. At commercial broadcast frequencies the ground wave may be overridden by unreliable sky waves.

• The station selected must be of relatively high power and low frequency for best results in ADF use.

• Frequency range 550 to 1660 KHz


NON DIRECTIONAL BEACONS

• The NDB is a low to medium-frequency navigation aid primarily intended to provide a broadcast signal to a mobile direction finder.

• The NDB radiates an omnidirectional signal.

• Low-powered NDB’s are installed at some marker sites to assist pilots in transitioning to the approach aid. The low-powered NDB has an effective range of 15 to 20 miles.

• High powered NDB’s are used as outer marker compass locators at some locations. (They are co-located at the outer marker of the ILS)

• Compass locators transmit 2- letter ID groups. (Morse ident).

• Frequency range 190 to 550 KHz.


HOW ADF WORKS

• The pilot selects the frequency of a ground station.

• This is confirmed by its morse ident or audio identification.

• Using charts, the pilot can plot his direction to the beacon. Using multiple beacons, the pilot can triangulate his position.

• The pilot may use the bearing information to fly to the ground station if it is on his flight path.


HOW ADF WORKS

• ADF uses two fixed loop antennas, one of which is perpendicular to the other, and a sense antenna.

• The antennas are mounted in the aircraft so that a signal can be received in one or both loop antennas without manoeuvring the aircraft.

• The relationship between direction and magnitude of signal of the voltages induced in each antenna is processed by the sense antenna and transmitted to the receiver.

• This information is processed into a signal to drive the needle to the correct bearing on the indicator.


TRANSPONDER


TRANSPONDER

• The airborne transponder is an important part of the air traffic control system being used today.

• The safety of passengers, aircraft and crew depends on the ability of air traffic controllers to locate aircraft within controlled airspace.

ATC

A transponder is the airborne receiver - transmitter portion of the ATC (Air Traffic Control) beacon radar system. It sends an identifying coded signal, in response to a transmitted interrogation from a ground based radar station, in order to locate and identify the aircraft.

Air traffic controllers use the coded identification replies of transponders to differentiate between the targets (aircraft) displayed on their radar screens. Being able to identify the aircraft aids the controller in maintaining aircraft separation, collision avoidance, and distinguishing types of aircraft.

The airborne portion of ATC consists of a transmitter/receiver (transponder), a control unit, a digitiser and an antenna.

The ground facility consists of a primary radar station, a secondary surveillance radar and a display unit (radar screen).



C O TR O L U N IT TR A N S P O N D E RTR A N S M ITTE R /

R E C E IV E R

A N TE N N A D IG ITIZ E R

A TCA IR C R A F T S Y S TE M


CONTROL UNIT

• The control unit contains the circuits to allow the operator to select the identifying code (0000 to 7777).

• It also contains the controls necessary to select an altitude source, initiate a self test mode and select the transponder reply mode.

(mode A, C & S).

• Indicators on the control unit will display the code selected.

• An ident button is also available to highlight the aircraft on the ATC display.


TRANSMITTER/RECEIVER

• The receiver part of the transponder contains the circuitry to receive, demodulate, amplify, and decode the interrogation signal.

• The transmitter part of the transponder is comprised of the circuits necessary to encode , modulate, amplify, and transmit the coded reply signal.

• The transponder also contains the circuits required for checking the validity of the received interrogation signal and for monitoring the integrity of the transponder.

DEPENDENT POSITION DETERMINNG

ANTENNA

• The antenna is an L-band (radio frequency band from 390 to 1550 Mhz), monopole blade type.

• It is usually mounted in an area of the aircraft that will not be shielded from interrogation. This prevents the aircraft’s identification from disappearing from the controller’s radar screen.


DIGITIZER

• The digitizer is a simple converter that converts an analog signal, representing barometric altitude, to a digital format.

• The digitiser barometric altitude can then be encoded and shipped as part of the reply signal.

• This may be done inside the barometric altimeter or alternately in an air data unit.


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PRIMARY RADAR

• The primary radar system works like many other radar systems. A narrow RF (radio frequency) type beam, transmitted through a rotating antenna, is reflected by targets in its path and returned to the antenna.

• By calculating the elapsed time between transmission and reception of the RF beam, the distance to the target is determined.

• The angle of the antenna is also noted so that the bearing to the target can be determined.

• This information is displayed on a 2- dimensional radar screen.


SECONDARY SURVEILANCE RADAR

• The SSR system interrogates the aircraft about its identity and altitude by transmitting two sets of pulses. The first set is mode A and the second mode C.

• Mode A pulses are 8 microseconds apart and interrogates the transponder about the identity of the aircraft.

• Mode C pulses are 21 microseconds apart and interrogate the transponder about the aircraft altitude.

• There are two other optional modes (mode B and mode D) for transmitting the aircraft identification and altitude.

DEPENDENT POSITION DETERMININGRADAR SCREEN

• The received signal from the primary radar and SSR is electronically encoded so that it can be displayed on a controllers radar screen.

• The type of radar screen is called a planned position indicator (PPI).

• The images on a PPI remain on the screen until the next sweep of the screen. In this way the controller does not have to remember aircraft positions between sweeps.

• The ground controller selects the identification codes he is interested in. If the controller is not interested in a particular aircraft its code will not be displayed.


HOW ATC WORKS• The pilot selects an identification

code, or is instructed to select a code by the air traffic controller.

• The SSR system transmits a coded interrogation signal (at 1030 Mhz) as the primary radar detects the aircraft.

• The interrogation signal is received, detected and decoded by the airborne transponder.

• The transponder then encodes and transmits a set of reply signals. (depending on the mode and code selected)

• The reply signal is the received, decoded and displayed at the ATC ground station.


VHF OMNIDIRECTIONAL RANGE

VOR


INTRODUCTION

• The VHF omnidirectional range (VOR) is a radio navigation system. VOR is used for position-fixing, maintaining course track and navigating along established airways. Basically, it provides the ability to follow a roadway in the air.

VORThis is a system used to determine the relative bearing from the aircraft to a ground based transmitter (with respect to the aircraft centre line).

The VOR transmitter produces a carrier wave and a variable signal which is shifted in phase.

The VOR navigation receiver detects the VOR radial signal and separates the reference and variable signals. The phase of the variable signal is then compared to the phase of the reference signal.

The phase difference is proportional to the radial angle from the VOR station. The bearing is then determined from this phase difference. From the determined bearing and the compass input to the indicator, aircraft heading and ground station bearing are displayed on the indicator.



C O N TR O L U N IT V O R IN D IC A TO R R E C E IV E R A N TE N N A A IR C R A F TC O M M S

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CONTROL UNIT• The control unit provides the

necessary control and switching circuits for a VHF navigation system.

• The control unit may also provide frequency selection for VHF comms and distance measuring equipment (DME).

• The control unit selects the VHF localiser frequency which automatically selects the paired UHF glideslope frequency and DME frequency (if co-located with a NAV system).


INDICATOR• There are two basic types of indicator used

in the VOR system. The RMI (Radio magnetic indicator) and the HSI (Horizontal situation indicator).

• The RMI will have a needle rotating against a rotating azimuth card, to indicate the bearing to a ground station, relative to the nose of the aircraft.

• The HSI will have a movable course pointer, a steering bar and a to-from arrow. The steering bar indicates the direction to be steered to bring the aircraft in track with the beacon. If the steering bar is central then that is the course to the beacon. The to-from arrow indicates whether the aircraft is flying towards or away from the beacon.


RECEIVER• The receiver contains the necessary

circuits for receiving, decoding and processing the bearing information from the transmitted VOR signal.

• The receiver also contains self monitoring circuits that confirm the validity of the received signals and the reliability of the bearing information sent to the indicator.

• Most VOR receivers also contain circuits required to decode and process lateral and/or vertical guidance information from an ILS ground facility.

• It may also process DME and marker beacon information.


ANTENNA• The typical antenna used by a VOR

navigation system is a bat-wing type antenna, with an omnidirectional, horizontally polarised radiation pattern capable of receiving VHF signals in the 108 to 118 MHz range.


COMMS• The ground station sends out an audio signal (morse code) every 30

seconds.

• This identifying signal is sent through the aircraft comms system to allow the crew to identify the VOR beacon that is being tracked.

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ANENNA• The VOR ground station transmits

continuously and is capable of handling all aircraft within the limits of the ground station transmitter and the capability of the aircraft’s receiver.

• The ground station provides voice transmission and an identifying code to ensure that the desired VOR station is being monitored.

• The identification signal (in morse code) is a 2 or 3 letter word repeated every 30 seconds.


HOW VOR WORKS• The pilot selects the frequency of a

ground station.• This is confirmed by its morse ident.• The phase difference between the

carrier wave and the variable signal is computed and an output signal is sent to the indicator.

• Using charts the pilot can plot his direction to the beacon. Using multiple signals the pilot can triangulate the position of the aircraft.

• The pilot may use the bearing information to fly to the ground station if it is on the aircraft flight path.

DEPENDENT POSITION DETERMINNG

DISTANCE MEASURING EQUIPMENT

DME


INTRODUCTION• Distance measuring equipment (DME) is a

system combining ground based and airborne equipment to measure the distance of the aircraft from a ground facility. DME is used primarily for position fixing, enroute separation, approach to an airport, avoiding protected airspace, holding at a given position or figuring ground speeds


DME

This is an airborne and ground based system, that measures the slant range of the aircraft from the ground station. The DME frequency if not manually selected, is automatically selected when an ILS/VOR frequency is selected, (the DME station being co-located with the ILS/VOR beacon).

Since the speed of a radio wave is a constant and known factor, the amount of time the signal travels is proportional to the distance. The airborne portion of the DME measures the amount of elapsed time and converts this to the distance (slant range) between the aircraft and the station.

DME indicators may also show time to station (TTS) and/ or computed ground speed.


C O N TR O L U N IT TR A N S M ITTE R /R E C E IV E R

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CONTROL UNIT• The control unit provides the necessary switching circuits for the

airborne DME.

• The control unit may also provide the frequency selection for VHF comms.

• Control units that provide frequency selection for more than the DME automatically select the DME operating frequency for the NAV receiver selected.

DEPENDENT POSITION DETERMINIG

TRANSMITTER/RECEIVER• The transmitter section of the unit

contains all the necessary circuits to generate, amplify and transmit the interrogating pulse pairs.

• The receiver section contains the circuits required to receive, amplify and decode the received reply pulses.

• This information is then sent to the indicator.

DEPENDENT POSITION DETERMIING

INDICATOR• The distance indicator displays the

aircraft distance in nautical miles from the ground station (slant angle).

• The indicator will also display, in the form of a flag or dashes (on digital indicators), as a warning that the system is either malfunctioning or not locked on to the reply signal.

• On some types of indicators, the information displayed also includes a computed ground speed and the time to station (TTS). These are only accurate if the aircraft is flying on a radial from the ground station.


ANTENNA• The antenna is a single L-band

(radio frequency band from 390 to 1,550 Mhz) transmit and receive antenna with an omni-directional pattern.


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GROUND STATIONS• There are several different types of

ground station (eg VOR/DME, ILS/DME).

• VOR/DME is DME located with a VOR station.

• ILS/DME is DME located with an ILS station.

• Ground stations are capable of handling 100 interrogations at one time. If more than 100 aircraft interrogate the ground station, the ground station limits its sensitivity and responds to the strongest interrogations.


HOW DME WORKS• The pilot selects an ILS/VOR frequency.

This automatically selects the DME frequency paired with that frequency.

• The receiver/transmitter of the airborne DME transmits interrogating pulse pairs.

• The ground facility receives these pulse pairs, delays 50 microseconds, and then transmits reply pulse pairs back to the airborne DME.

• The airborne receiver/transmitter receives the reply pulse pairs and verifies that they are valid.

• Then it calculates the distance• This is sent to the indicator for the pilot• This cycle continues until the frequency

is changed or the aircraft is out of range.

AUTOPILOT

INTRODUCTION

• The autopilot system, when selected, reduces the workload of the pilot. It controls and physically flies the aircraft.

AUTOPILOT

The autopilot system comprises two main systems, the flight director and the aircraft control system.

The flight director side of the system takes the selected operational mode and, using the output of the autopilot computer, displays the steering information required to fly the aircraft.

The aircraft control system, takes the output from the autopilot computer and, using a set of servos, moves the aircraft controls, physically flying the aircraft in the mode selected.

AUTOPILOT

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FLIGHT DIRECTOR• The basic flight director uses modes

selected by the pilot to display steering information. If the selected mode is flashing, it is in standby, becoming steady when it is operational.

• HDG :- using the heading bug on the HSI then the steering information from the computer will be outputted to intercept and fly along that heading .

• NAV :- the nav selection will flash until the selected VOR beacon is found. Then the steering information from the computer will be outputted, to intercept and fly along that heading .

• APPR :- the appr selection will flash until the selected ILS beacon is found. Then the steering information from the computer will be outputted, to intercept and fly along that heading .

FLIGHT DIRECTOR• ALT :- when selected, will try and

maintain the aircraft at the altitude it was selected. This is a barometric altitude selection.

• IAS :- will try to maintain the aircraft’s indicated air speed, by changing the aircraft’s attitude.

• B/C :- back course, disabled on many autopilot systems, allows the aircraft to be flown at the ILS beacon from the reverse direction. Only localiser information is given. It will flash until the selected ILS beacon is found then the steering information from the computer will be outputted, to intercept and fly along that heading .

FLIGHT DIRECTOR

• ENG/DIS :- this switch engages or disengages the autopilot. The green triangle next to the switch indicates the autopilot is engaged and the amber that it is disengaged.

• Trim UP/DOWN :- flashing amber lights indicate when the autopilot is trimming the aircraft either up or down. If the system is run in flight director mode only or if there is no trim output function to a servo, then these lights will come on (not flashing) to indicate that a manual trim is required.

• DIM :- this is a rotary switch to dim the

display lighting.

AUTOPILOT COMPUTER

• The autopilot computer contains the necessary circuits to take information from navigation sources, process it and then produce steering information to the flight instruments and control servos.

• If the system only produces steering information to the flight instruments, then it is a flight director system, not an autopilot.


• The command bars on the attitude & director indicator will show the angle of bank required to pick up the selected nav source.

• When in true autopilot, the aircraft’s attitude will match that of the command bars.

• The glideslope and the localiser

pointers will be displayed during appr mode and indicate the aircraft’s position relative to the ILS signal. In appr mode in a true autopilot system it will fly down the centre of the glidepath.

HOROZONTAL SITUATION INDICATOR

• This allows the heading to be flown by manually selecting the heading bug to the desired heading.

SERVOS

• There are various servos to control the aircraft’s flying control surfaces.

• Aileron servo :- controls the aircraft roll.

• Elevator servo :- controls the aircraft pitch.

• Trim servo :- controls the aircraft trim

• Rudder servo :- controls the aircraft rudder.

• The servos can all be overridden by manual inputs into the system. This is achieved by having a capstan fitted with a breakout torque.

PITCH/TURN CONROL

• This allows pitch and turn information to be manually inputted into the autopilot system without disengaging the autopilot.

• Pitch control :- this is used to command the a pitch rate proportional to knob displacement. Rotating the control up or down produces a pitch command. The aircraft will hold the pitch last selected. The pitch control is spring loaded to centre, giving a pitch hold mode.

• Turn control :- this is used to command the roll rate proportional to knob displacement. Rotating the control left or right produces a roll command. The aircraft will hold the roll last selected. The pitch control is spring loaded to centre, giving a roll hold mode.

HOW AUTOPILOT WORKS

• The pilot selects the autopilot mode required.

• The autopilot computer takes the relevant steering information or nav source and computes the steering information required by the servos to make the aircraft fly in the selected mode. It also sends out the steering information to the aircraft instruments giving the pilot a visual indication of the autopilot commands.

• As the autopilot nears its desired track/ heading it automatically reduces its rate of turn, so that it can intercept the course without over swing.

DHC-6 TWIN OTTER AVIONICS FOR DUMMIES

Documents

Basic Avionics Presentation