B1_M11.05.02_2008.11.27 Avionics Systems.pdf

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Author:
For Training Purposes Only
LTT 2006
E
Avionic Systems
(ATA 23, 34, 31, 22)
EJAMF_M11.05.02_B1_E
eJAMF
Fundamentals
1MAR2007
SwD
EASA Part-66
B1
Module 11.05.02
27.11.2008

Training Manual
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Page 1
ATA DOC
M15 GAS TURBINE ENGINE EJAMF
Gas Turbine Engine
MODULE 15
HAM US/F-4 SaR 01.06.2007
EJAMF M15.01 FUNDAMENTALS
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01|Communica Sys Overv/ALL
COMMUNICATIONS
INTRODUCTION
FUNDAMENTALS
ATA 23
HAM US/F-4 SaR 01.06.2007
COMMUNICATIONS
INTRODUCTION
COMMUNICATION SYSTEMS OVERVIEW
In this unit we will show you the communication systems of modern aircraft. We
can divide the systems into three groups.
The systems for the communication inside and outside the aircraft are called
the interphone and passenger address systems.
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Figure 1 System Overview

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Communication Systems Overview cont.
The radio communication systems are called the VHF system, the HF system,
the SATCOM system and the ACARS system.
Finally two systems are used for accident investigation. These are the voice
recorder and the emergency locator transmitter or ELT in short.
The interphone system allows communication between the cockpit and other
areas of the aircraft, for example for maintenance.
The passenger address system allows the flight and cabin crew to give
announcements to the passengers, for example for flight safety.
The VHF communication system allows communication via radio signals over a
distance of up to 200 nm (nautical miles), for example with Air Traffic Control or
other aircraft.
The HF system allows communication over long distances because HF radio
signals are reflected by the ionosphere of the earth.
The satellite communication system (SATCOM) allows the cockpit crew to
communicate over the whole world. It is also used by any passenger
pay−phone services on board the aircraft.
ACARS stands for aircraft communication, addressing and reporting system. It
allows exchange of information like flight and maintenance data between
aircraft and the ground. It uses VHF, HF or SATCOM for communication with
the ground station.
The cockpit voice recorder system or CVR stores all communications of the
flight crew for later accident or incident investigations.
The emergency locator transmitter, or ELT in short, can help to find the location
of the airplane after an accident.
The main components of the communication systems are located in the
cockpit:
S On the pedestal both pilots are provided with a radio management panel, or
RMP in short, for frequency selection of the radio communication systems
S and an audio control panel, or ACP in short, to select the different systems
for the headphone and microphone.
Additional control functions for the communication systems are located on the
overhead panel and in the cabin.
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Figure 2 Radio Communication Systems

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Communication Systems Overview cont.
The cockpit voice recorder system or CVR stores all communications of the
flight crew for later accident or incident investigations.
The emergency locator transmitter, or ELT in short, can help to find the location
of the airplane after an accident.
The main components of the communication systems are located in the
cockpit:
S On the pedestal both pilots are provided with a radio management panel, or
RMP in short, for frequency selection of the radio communication systems
S and an audio control panel, or ACP in short, to select the different systems
for the headphone and microphone.
Additional control functions for the communication systems are located on the
overhead panel and in the cabin.
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Figure 3 Accident Investigation Systems

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04|Radio Frequenc/ALL
COMMUNICATIONS
INTRODUCTION
FUNDAMENTALS
ATA 23
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RADIO FREQUENCIES
Any kind of communication needs 2 things. The first is the information you want
to exchange and the second is the carrier of the information.
The carrier could be either paper, like a letter, or a CD-ROM for digital data, or
a wire like a telephone line.
In the aircraft the interphone, the passenger address and the cockpit voice
recorder system use wires as the carrier to transport the information.
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Figure 4 Radio Frequencies

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Radio Frequencies cont.
All other aircraft communication systems need a wireless carrier to allow
communication during flight.
This carrier is a radio frequency or RF signal.
The radio frequencies that are used in aviation are divided into 8 frequency
bands.
The very low frequency or VLF band ranges up to 30 kHz. This band is only
used in military communication systems as a radio frequency but it is also used
for audio signals.
The low frequency or LF band is between 30 kHz and 300 kHz. It is not used
for aircraft communication systems, but is used by public radio stations and the
ADF navigation system.
The medium frequency or MF band is between 300 kHz and 3000 kHz which
corresponds to 3 MHz. It is not used for aircraft communication systems, but is
used by public radio stations and the ADF navigation system.
The high frequency or HF band is between 3 MHz and 30 MHz. It is used by
the HF communication system and allows communication over long distances.
The very high frequency or VHF band is between 30 MHz and 300 MHz. It is
used by the VHF communication system which allows communication over
distances up to 200 nm (nautical miles). It is also used by navigation systems
like the VOR and ILS.
The ultra high frequency or UHF band is between 300 MHz and 3000 MHz
which corresponds to 3 GHz. This band is only used by military communication
systems and by radar systems like DME, ATC and the GPS navigation system.
The super high frequency or SHF band is between 3 Ghz and 30 Ghz. It is
used by the satellite communication system, and the weather radar and radio
altimeter which belong to the navigation systems.
The extremely high frequency or EHF is between 30 GHz and 300 GHz. It is
not used for communication or navigation systems.
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FUNDAMENTALS
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ELT
VHF
HF
SATCOM
ACARS
Radio
Communication
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Figure 5 Frequency Bands

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06|Wavelength/ALL
COMMUNICATIONS
INTRODUCTION
FUNDAMENTALS
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WAVELENGTH
A full wave of an alternating current, also called a cycle, has a certain length in
time called Period T.
You can calculate T as the reciprocal value of the frequency. So the period of a
frequency of 1Hz is 1 second.
When you activate an AC on an endless wire, then the electric force will travel
with the speed of light c which is 300 000 km in 1 second.
This means that the areas with negative polarity and positive polarity travel
with this speed.
The areas with a high concentration of electrons correspond to the negative
peak of the voltage and areas with a low concentration correspond to the
positive peak.
The wavelength is now defined as the distance between two areas of high or
low electron concentration.
For a frequency of 1Hz this distance would be 300 000km because this is the
distance the electrical force can travel in 1 second.
Generally you can calculate lambda by multiplying the period with the speed of
light c or by dividing c by the frequency.
We have added the wavelength to each frequency band. You probably know
that the wavelength is often used to identify a certain frequency band.
For example in a microwave oven the term microwave means that extremely
high frequencies are used.
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06|Wavelength/ALL
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Figure 6 Wavelength

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07|Wave Propag&Modulat/ALL
COMMUNICATIONS
INTRODUCTION
FUNDAMENTALS
ATA 23
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WAVE PROPAGATION & MODULATION
Wave Propagation
Radio waves travel differently depending on the frequency. This is called the
wave propagation.
High frequencies only travel in a direct line, with the so called sky wave so they
can only be used when transmitter and receiver have contact within a visual
range.
On earth this is possible up to a distance of 200nm.
For SATCOM, which uses the SHF band, you need satellites to allow reception
around the earth.
The lower the frequency, the better the propagation around the world with a
ground wave.
Military systems use this advantage in the VLF and LF band.
In commercial aircraft the HF band is used for communication around the
world. In this band the skywave is partially reflected by the ionosphere and
returns to the ground. Reception quality is not always good because daytime
and selected frequency influence the reflection.
Modulation
To transport information with the radio frequency carrier we must modulate the
carrier frequency with the signal frequency, which is for example the audio
signal. This signal has a frequency in the range of up to 30kHz and is called
audio frequency or AF.
When the amplitude of the carrier wave is varied, this is called amplitude
modulation or AM in short.
When the frequency of the carrier wave is varied, this is called frequency
modulation or FM in short.
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07|Wave Propag&Modulat/ALL
COMMUNICATIONS
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Figure 7 Wave Propagation & Modulation

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08|Audio Components/ALL
COMMUNICATIONS
INTRODUCTION
FUNDAMENTALS
ATA 23
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AUDIO COMPONENTS
For communication in aircraft we need two general components for nearly all
systems:
Microphones transfer the acoustic information into an electrical signal.
Loudspeakers transfer the electrical signal back into acoustic information.
Different types of microphone are used in the cockpit.
S An area microphone is used by the voice recorder to record the general
cockpit sounds,
S a hand−held microphone is used for announcements to the passengers
S and integrated microphones are contained in the oxygen mask or the
headset. These are then called boomset.
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Figure 8 Audio Components

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Audio Components cont.
Loudspeakers are used in the cockpit for warning sounds.
Small loudspeaker types are used in headsets and boomsets. Boomsets
contain a combined microphone and loudspeaker.
In the cabin you can find loudspeakers in the ceiling for passenger information
and entertainment programs.
In addition the cabin crew uses telephone type handsets with a small
loudspeaker and microphone for internal communication and passenger
announcements.
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Loadspeaker
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Figure 9 Audio Components

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10|Radio Components/ALL
COMMUNICATIONS
INTRODUCTION
FUNDAMENTALS
ATA 23
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RADIO COMPONENTS
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Figure 10 Transmitter Components

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Radio Components cont.
A receiver has 3 main components:
S a tuning circuit which selects only one frequency from the total antenna
output. This frequency is selected on the control panel;
S a demodulator which recovers the audio signal from the RF signal;
S an audio amplifier which generates the necessary power for the audio
equipment.
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Figure 11 Receiver Components

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Antennas are needed to receive or transmit the RF carrier.
Aircraft antennas have different sizes and locations. The location depends on
the task of the system and the size depends mainly on the carrier frequency.
This is because an antenna is most effective when its length is a minimum of a
quarter of the wavelength.
The VHF COM frequency range is between 118MHz and 137MHz. This
corresponds to a wavelength between 2.45m and 2.19m Therefore
theoretically the required antenna length should be between 55cm and 64cm.
As this difference is very small we could use a fixed antenna length of about
60cm without losing effectiveness. In modern aircraft you can find VHF
antennas which are shorter than 60cm like this one on the picture. This is
possible because you can lengthen an antenna with electronic components.
This saves weight and reduces the drag.
The frequencies of the HF communication system range from 2MHz to 30MHz.
Therefore the length of the antenna should be between 2.5m and 37.5m. This
big variation does not allow the use of a fixed average length.
The HF antenna, which has for example a length of 2m, must be electronically
lengthened depending on the used frequency.
This is done by an antenna coupler.
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VHF
HF
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Figure 12 Antennas

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The connection between the transceiver and the antenna is made by special
feeders called RF lines.
Two different types are used in aircraft.
S The first type is a co−axial cable type which is used for frequencies of up to
3 GHz. It has an inner conductor which carries the RF potential and an
outer conductor which is grounded. A filler material insulates both
conductors from each other.
S The second type are waveguides. These are used above 3 GHz and are
special feeders for radar frequency signals.
All RF lines must only be handled by specially trained personnel according to
the instructions in the maintenance manual.
Note that transport of the radio signals is disturbed by deformations of the
RF−lines.
Water in the RF line and corrosion of the contacts will do the same.
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Figure 13 RF Lines

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14|Static Discharger/ALL
COMMUNICATIONS
INTRODUCTION
FUNDAMENTALS
ATA 23
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STATIC DISCHARGER
Aircraft are equipped with static dischargers at all sharp trailing edges of the
airframe. In these areas the friction with air during flight generates static
electricity.
This static electricity must continuously be discharged to prevent build−up of
high voltages on the fuselage because this would damage electronic equipment
and disturb reception of radio signals.
The maintenance manual states how many static dischargers must work
properly to guarantee correct operation.
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14|Static Discharger/ALL
COMMUNICATIONS
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01|Audio Management Sys/ALL
COMMUNICATIONS
AUDIO SYSTEMS
FUNDAMENTALS
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AUDIO SYSTEMS
AUDIO MANAGEMENT SYSTEM
The audio management system controls all functions necessary for crew
communications.
In modern systems a central computer called the audio management unit, or
AMU in short, connects the audio equipment of the captain, the first officer and
a third crew member with the radio communication and navigation systems.
The AMU also allows each crew member to communicate with the other flight
crew members via the flight interphone system.
For communication with the cabin crew the cabin interphone system is used
and for communication with maintenance staff at connections in several areas
of the aircraft the service interphone system is used.
In addition the passenger address system, or PA system in short, allows the
pilots to make announcements to the passengers.
Finally the AMU transfers all relevant signals to the cockpit voice recorder.
Each crew member has an audio control panel, or ACP in short, to select the
necessary communication channel for their own audio equipment.
The panels for the captain and the first officer are located on the pedestal and
the panel for the third crew member is either on the overhead panel or located
on the pedestal. In some aircraft types you can also find a fourth audio control
panel in the cockpit and even one in the avionic compartment.
The audio equipment for each cockpit crew member consists of a headset,
boomset and microphones inside the oxygen mask and in a handheld version.
Note that the oxygen mask microphone has priority over the boomset
microphone when the mask is in use.
To use the boomset again you must first restore the oxygen mask in the
stowage box and reset the oxygen mask flag.
Loudspeakers make the selected audio audible in the whole cockpit. The pilots
can adjust the audio volume with a control knob near the loudspeaker or on the
audio control panel.
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01|Audio Management Sys/ALL
COMMUNICATIONS
AUDIO SYSTEMS
FUNDAMENTALS
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Figure 15 Audio Management System

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02|Audio Control Panel/ALL
COMMUNICATIONS
AUDIO SYSTEMS
FUNDAMENTALS
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AUDIO CONTROL PANEL
The ACPs allow a separate selection of reception and transmission channels.
The transmission selection is done by push−buttons. Only one system can be
selected at a time which is shown by a light in the selected push-button.
For the reception selection you must release the corresponding rotating knob
by pressing on it. After the knob is released you can now select the audio
volume. It is possible to select more than one system at the same time.
With a sidetone you can always monitor the transmitted audio with the
reception channel.
For the communication systems you can select the reception and transmission
function but for the navigation systems only reception is possible.
There are 3 VHF transceiver selectors for radio communication, for the left,
center and right systems. In other aircraft they are called systems 1, 2 and 3.
There are 2 HF transceivers for radio communication. These are either the left
and right systems or systems 1 and 2.
The flight interphone knob selects the channel to communicate with the other
flight crew members.
The cabin knob selects the cabin interphone channel to communicate with the
cabin crew.
You can also select the service interphone function when the aircraft is on
ground.
The PA knob selects the passenger address system to allow announcements
to the passengers.
The SATCOM knob selects the satellite communication system to allow
telephone calls.
Audio information from the navigation systems is needed to identify the
selected station by Morse code and to get additional voice information.
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AUDIO SYSTEMS
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Figure 16 Audio Control Panel 1

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AUDIO SYSTEMS
FUNDAMENTALS
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Audio Control Panel cont.
You can select the VOR or ADF navigation system and the ILS or marker
beacon system.
You can influence the received signals using the filter selector.
When the switch is in the V−position you will only receive the voice information
and in the R-position, which stands for range, you will only receive the
identification code.
In the B-position you receive both audio signals at the same time.
The audio control panel also has a radio transmission or RT switch with 3
positions. The switch position decides whether you transmit or receive audio
with the selected communication system.
In the center position the selected communication system is in the reception
mode, so you can hear the received audio from the system.
The spring-loaded up position selects the transmission mode. This is also
called the push-to-talk or PTT function. You need to activate this switch when
you want to use the microphones in the boomset or oxygen mask. Only the
handheld microphone has its own push-to-talk switch.
In the Interphone position the microphones are permanently connected to the
flight interphone system, so the pilots can talk to each other independently of
the other selections.
All modern audio control panels have basically the same functions. Our
example on the left is used in modern long distance Boeing aircraft and you
can find the panel on the top right on long distance Airbus aircraft.
The audio control panel on the bottom right is used in short distance Boeing
aircraft; therefore it has no switches for the HF and SATCOM systems.
One main difference on the 2 panels on the right is that a voice only
push-button controls the audio filter. Pressing the switch cancels the Morse
code so this corresponds to the V-position of the filter selector on the left panel.
Instead of the radio transmission position of the switch on the audio control
panels the pilot can also use a push-to-talk switch on the control wheel or
sidestick.
On some control wheel switches you can also select the permanent interphone
position.
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Figure 17 Audio Control Panel 2

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04|Audio Switch/ALL
COMMUNICATIONS
AUDIO SYSTEMS
FUNDAMENTALS
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AUDIO SWITCHING
If there is a malfunction in captain’s or first officer’s transmission or reception
circuits in the AMU or ACP, they can transfer their audio equipment to the
circuits of the third crew member.
This is done with a transfer switch usually located on the overhead panel.
After the transfer the pilot must use the audio control panel of the third crew
member.
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04|Audio Switch/ALL
COMMUNICATIONS
AUDIO SYSTEMS
FUNDAMENTALS
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NORM
F/O
3
CAPT
3
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Figure 18 Audio Switching

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05|Interphone Sys/ALL
COMMUNICATIONS
AUDIO SYSTEMS
FUNDAMENTALS
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INTERPHONE SYSTEMS
The flight interphone system is used for communication between the cockpit
crew members.
In addition the communication with a mechanic on the ground is possible via a
boomset connection near the nose gear. This is used for example during the
push back from the gate.
When the mechanic wants to communicate with the cockpit, he or she must
press the call push-button near the jack.
This illuminates the mechanic call light (MECH) on the audio control panel
accompanied with a short audio tone.
You can connect your microphone to the flight interphone system by either
selecting the FLT push-button or by switching the radio transmission switch to
the interphone position.
The headphones are connected to the flight interphone system by releasing the
corresponding knob.
The mechanic call is reset automatically after a time limit or the pilot can
manually reset it by selecting a reset push−button.
The attendant light illuminates on the audio control panel when a cabin
attendant wants to communicate with a cockpit crew member. The light is also
accompanied by a short audio tone.
Pushing the cabin push-button connects the microphone to the cabin
interphone system and releasing the knob connects the headphone to the
cabin interphone system.
The reset of the call is again automatic or done by selecting the reset
push-button.
The service interphone system is used primarily by maintenance personnel to
connect the cockpit to various areas inside or outside the aircraft.
It uses the cabin interphone channels of the audio management system, so the
same selections are necessary for the service interphone.
As the service jacks are often located in areas with high moisture and dirt they
are only connected to the interphone system on ground.
This is done either automatically by the air−ground sensing circuit or by a
switch on the overhead panel.
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Page 40
06|Passenger Address Intro/All
COMMUNICATIONS
AUDIO SYSTEMS
FUNDAMENTALS
ATA 23
HAM US/F-4 SaR 01.06.2007
PASSENGER ADDRESS INTRODUCTION
The purpose of the passenger address system, or PA System in short, is to
give information to the passengers.
Information can come from the cockpit or cabin crew or from a tape player
used for pre−recorded announcements.
Also, when available, boarding music can be played in the cabin.
Finally the PA system generates chimes as attention getters.
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07|Passenger Address Sys/ALL
COMMUNICATIONS
AUDIO SYSTEMS
FUNDAMENTALS
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PASSENGER ADDRESS SYSTEM
The PA system uses PA amplifiers, which are located in a separate unit or part
of a modern cabin communication systems called, for example, CIDS or
ACESS.
The PA amplifiers give the inputs a different priority to prevent a mixture of the
audio signals.
The highest priority is the input from the cockpit crew and the second priority is
the purser followed by the other cabin crew members. The fourth priority is the
pre−recorded announcements and the least important input is the boarding
music.
The PA system also generates chimes as attention getters. They are not
included in the priority circuit, so they will always sound in addition to other
audio.
A high chime sounds when a passenger calls the cabin crew and a high − low
chime sounds when one cabin crew member calls another crew member or the
cockpit.
A low chime comes on when the Fasten Seatbelt or No Smoking signs are
switched on.
The PA amplifier can increase the audio volume to make sure that all
announcements can be heard clearly by the passengers.
First the output increases when an engine is started, usually detected by the
engine oil pressure switch.
The volume level is further increased when the oxygen masks are released
after a cabin decompression; it is triggered by the 14000ft pressure switch.
To make a PA announcement from the cockpit the pilot must press the PA
push-button on the audio control panel. On some aircraft types this push-button
must be held for the duration of the announcement.
Often there is an additional handset especially for PA announcements. This
bypasses the audio control panel.
All PA audio can be heard by the pilots when the PA knob is released. With this
sidetone the pilot can check that his own announcement is transferred to the
cabin loudspeakers and that cabin crew announcements are not interrupted.
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08|CVR System/All
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AUDIO SYSTEMS
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COCKPIT VOICE RECORDER SYSTEM
The cockpit voice recorder, or CVR in short, is a very important component for
evaluation of aircraft incidents or accidents because it keeps a continuous
record of all cockpit crew communications and sounds in the cockpit.
Two different types of voice recorders are presently in use.
The analogue tape recorder stores the last 30 minutes of the flight on an
endless tape. Older recordings are automatically erased.
The digital solid state recorder stores the last 120 minutes of the flight in a
memory. Here previous recordings are also automatically overwritten.
The cockpit voice recorder system usually has the following components:
S the recorder itself which is located near the flight data recorder; usually in
the tail section of the aircraft;
S a control panel usually located on the overhead panel;
S an area microphone which is either located on the control panel or in a
separate location.
On the front of the recorder you can find an underwater locator beacon, ULB in
short.
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ULB
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09|CVR Operation/All
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CVR OPERATION
The cockpit voice recorder has 4 audio inputs. Three inputs come from the
audio management unit and correspond exactly to the audio which the flight
crew hear in their headphones. As all transmissions are also repeated in the
headphones the recording contains the reception and transmission.
The 4th input is the general cockpit sounds from the area microphone.
The voice recorder starts recording automatically when one engine is started or
when the aircraft is in flight at the latest.
The recording stops 5 minutes after shutdown of the last engine on the ground.
With the erase switch on the control panel you can erase the complete
recording when the aircraft is on the ground and the parking brake is set. This
is to keep the privacy of the crew.
You can test the voice recorder by pressing the test push button on the control
panel.
This starts the recorder and it records a test signal on all four channels. In
many aircraft types you need to activate the recorder power with the ground
control switch first.
During the test the pointer in the meter must deflect to the green area or a
status indicator must indicate pass. In modern aircraft the test is usually done
with the central maintenance computer system.
You can monitor a test recording when you connect a set of headphones to the
jack on the panel.
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Page 48
01|Intro/ALL
COMMUNICATIONS
VHF COMMUNICATION SYSTEM
FUNDAMENTALS
ATA 23
HAM US/F-4 SaR 01.06.2007
INTRODUCTION
The VHF communication system is used for short distance voice and data
communication with ground stations or other aircraft.
The VHF frequency range for aircraft communication systems is from 118MHz
to 136.975MHz.
Note that the frequency of 121.5MHz is an international emergency frequency
which is used for example by the emergency locator beacon. This frequency
should never be used for transmissions.
The spacing between each communication channel is normally 25kHz which
means that 760 frequencies, also called channels, are available.
In Europe more channels are required in high flight levels; therefore modern
systems use a channel spacing of 8.3kHz which means more than 2000
channels are available.
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Figure 24 VHF Communication System

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02|Sys Components/ALL
COMMUNICATIONS
FUNDAMENTALS
ATA 23
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SYSTEM COMPONENTS
Modern aircraft have 3 independent VHF systems. Two systems are a
minimum requirement for commercial flights.
System no.1 is normally used for the captain’s voice communication and
system no.2 for the first officer’s voice communications.
The third system is normally used for the ACARS system but it could also be
used for voice communication if one of the other systems fails.
Each VHF communication system has a transceiver in the avionics
compartment and an antenna.
The 3 antennas are installed at different locations on the aircraft fuselage.
Usually you can find the antennas for VHF systems no.1 and no.3 on the upper
fuselage and the antenna for VHF no.2 on the lower fuselage.
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Figure 25 VHF System Components

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System Components cont.
The VHF communication systems are controlled by radio management panels,
RMP in short, which allow frequency selections and by audio control panels
which allow audio selections.
The transceiver has both a transmitter and a receiver for either receiving or
transmitting signals.
You can hear a received signal with your audio equipment when you select the
corresponding knob on the ACP and the correct frequency on the RMP.
You must always listen to a selected station first before you start a
transmission to prevent communication interruptions with another aircraft.
To transmit information to the selected station you must push either the radio
transmission switch on the ACP or operate the push−to−talk switch on the
control wheel.
When the transmission works with the normal output power of about 25 W, you
can hear your own voice in the headphones with the sidetone.
A missing sidetone is always an indication for a system failure.
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Figure 26 VHF System Components

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04|Radio Manage Panel/ALL
COMMUNICATIONS
FUNDAMENTALS
ATA 23
HAM US/F-4 SaR 01.06.2007
RADIO MANAGEMENT PANEL
The radio management panel is the component where you make frequency
selections for the VHF and HF radio communication systems.
Each RMP can control any system. The selected system is shown by the light
in the pushbutton.
During normal operation the captain’s panel controls the VHF and HF systems
no.1 and the first officer’s RMP controls VHF and HF systems no.2.
The third RMP is usually used for VHF no.3.
The RMP has 2 frequency windows. The left window is called the active
window. It shows the operating frequency of the selected system.
The other is called the standby window which shows a new selected frequency.
Note that the window shows either ACARS or DATA when you select VHF
system no.3 because no manual frequency selection is necessary for ACARS.
When you press the transfer button on an RMP, the frequencies change
windows. This means that the standby frequency becomes the active
frequency and vice versa.
All RMPs are constantly updated by each other. When you activate a frequency
on one RMP, it is also visible on the other RMPs when the same system is
selected.
On some radio management panels, for example on modern Airbus aircraft,
you can find an area for the frequency selection of navigation systems. This is
only used when normal tuning via the flight management system is not
available.
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Figure 27 Radio Management Panel & Operation

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05|Sys Operation/ALL
COMMUNICATIONS
FUNDAMENTALS
ATA 23
HAM US/F-4 SaR 01.06.2007
SYSTEM OPERATION
Let us now see an example of how to establish a connection to a VHF ground
station.
First you must cross−check that the selection for your audio equipment is done
on your audio control panel and that the required VHF communication system
is selected on the radio management panel.
The required frequency is selected by turning the frequency selector knob. This
changes the frequency in the standby window.
After selection of the correct frequency you must activate the frequency for the
VHF system no.1.
Before you transmit your request to the VHF ground station listen to the
reception to make sure that no actual communication is in progress.
You can now start the transmission by activating one of the push−to−talk
switches.
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Figure 28 Radio Management Panel & Operation

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01|Intro/ALL
COMMUNICATIONS
HF COMMUNICATION SYSTEM
FUNDAMENTALS
ATA 23
HAM US/F-4 SaR 01.06.2007
INTRODUCTION
The HF communication system is used for long distance communication.
HF communication systems are installed on many long distance aircraft for
world wide communication.
The ionosphere around the world is used as a reflector for the radio signals to
reach areas outside the line of sight. Unfortunately the ionosphere changes its
conditions. For example the intensity of sunlight determines the quality of
reception.
In modern aircraft types the SATCOM system replaces the HF system because
it guarantees a reliable long distance communication.
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Figure 29 HF Communication

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02|HF Sys Comp/ALL
COMMUNICATION
HF COMMUNICATION
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HF SYSTEM COMPONENTS
Usually 2 independent HF communication systems are installed in long
distance aircraft.
Each system has a transceiver which is located in the avionics compartment
and an antenna which is usually located in the leading edge of the vertical
stabilizer.
On older aircraft types or aircraft with three HF systems you can also find a rod
type antenna at the wing tip.
An antenna coupler is needed to tune the antenna to the selected
HF−frequency.
It is installed near the antenna.
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HF COMMUNICATION
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Figure 30 HF System Components

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03|HF Sys Comp/ALL
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HF COMMUNICATION
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HF System Components cont.
The HF transceiver has a transmitter and receiver that functions in the same
way as the VHF transceiver. Transmission happens with an output power of
200W to 400W.
The frequency and system selection on the RMP is done in the same way as
for the VHF system.
The HF frequency range is from 2MHz to about 25MHz in steps of 1 or
0.1kHz.
With the AM push-button on the RMP you can select 2 different operational
modes for HF.
When the push-button is pressed the first time, the AM mode is selected. AM
stands for amplitude modulation. This mode transmits the modulated signal via
a carrier.
When the push-button is pressed again, the default SSB mode is selected.
SSB stands for single side band. This mode transmits the modulated signal
without a carrier giving a better transmission efficiency.
With the HF sensitivity selector knob on the RMP you can adjust the sensitivity
of the reception.
Note that some RMP types have a SQL knob instead. Here you can select the
squelch level which is the level for noise suppression.
On older aircraft types you can find a separate HF control panel with the same
control functions as described for the RMP.
The antenna coupler must tune the antenna to the selected HF frequency
before you can start any transmission. Reception is always possible without a
new coupler tuning.
Pressing briefly one of the push−to−talk switches for the first time will start the
tuning.
You can hear a 1kHz tone as long as the tuning lasts. The tuning is very fast in
modern systems but older systems need up to 10 seconds.
When the antenna coupler has completed the tuning, the 1kHz tone stops, and
you can start transmission by pressing the push−to−talk switch a second time.
You can monitor the correct transmission with the sidetone when normal
transmitting power is available.
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HF COMMUNICATION
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Old HF Panel
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04|HF Sys Operation/ALL
COMMUNICATION
HF COMMUNICATION
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HAM US/F-4 SaR 01.06.2007
HF SYSTEM OPERATION
You should be able to do the necessary steps to establish HF communication:
With the first step the audio equipment has to be connected to the HF system
no1.
On the audio control panel the audio equipment has to be connected to the
transmission and reception channel of HF no.1.
HF system no.1 has to be selected to AM mode on the RMP.
The selected frequency is now shown in the standby frequency window.
When the frequency is activated, you must first check if this frequency is busy
before you start a transmission.
Let us assume that no communication is in progress, so that you can start
tuning the antenna coupler.
Pressing the radio transmission or push−to−talk switch the first time after a new
frequency selection, tunes the transmitter and the coupler to the new
frequency.
When the tuning tone has stopped, you can start your communication with the
selected ground station.
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HF COMMUNICATION
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Figure 32 HF System Operation

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01|ACARS Intro/ALL
COMMUNICATIONS
DATA TRANSMISSION
FUNDAMENTALS
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DATA TRANSMISSION
ACARS INTRODUCTION
The aircraft communication addressing and reporting system or ACARS in
short, is a datalink communication system which can transfer messages and
data between the aircraft and the ground, for example the airline operation
center and ATC.
It uses the VHF Communication system no.3 or the satellite communication
system depending on the aircraft location.
In some modern aircraft types the HF system can also be used for ACARS.
The data sent by ACARS is received by the ground station of a network
provider which transports the data via its network to the user.
The data transfer in this direction is called the downlink. Consequently the data
transfer from the ground to the aircraft is called the uplink.
ACARS transmits and receives either automatic reports which usually depend
on the flight profile and manual reports which are independent of the flight
profile.
Automatic Reports
The OUT report transmits aircraft information and the time when all aircraft
doors are closed and aircraft movement starts.
The OFF report transmits aircraft information and the time when the aircraft
lifts off detected by the landing gear air-ground switches.
The ON report transmits aircraft information and the time when the aircraft
touches down detected by the landing gear air-ground switches.
The IN report transmits aircraft information and the time when the first aircraft
door is opened.
The estimated time of arrival, or ETA in short, is automatically transmitted
120min, 20min and 7min before arrival.
The aircraft condition monitoring system (ACMS) transmits an engine report
automatically during each flight and whenever an engine problem is detected;
for example an EGT exceedance.
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DATA TRANSMISSION
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ACARS Introduction cont.
Manual Reports
The loadsheet report is an uplink from the ground to the aircraft during take-off
preparation. Manual ACARS reports are started by the pilot, airline ground staff
or ATC.
A call request is transmitted to the aircraft if the ground station wants to
communicate with the flight crew via voice communication. This is used instead
of the old SELCAL system.
ATC will use ACARS in the future air navigation system (FANS) to send
requests to the aircraft, for example: Maintain speed. You will learn more about
FANS in the Navigation unit.
A report request is a downlink when the flight crew requires specific
information. These are, for example, airport or weather data, or information for
the passengers or crew.
Information for the crew or the passengers is an uplink as a response to a
report request. For example it gives information about the departure gates for
transit passengers and the next flight for the crew.
Maintenance reports can be started from the central maintenance computer
system (CMCS) to transmit test results or maintenance reports to the airline
maintenance center.
Manual Reports
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03|ACARS Operation/ALL
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ACARS OPERATION
A typical ACARS system has a central computer called the management unit,
or MU in short. It is the link between the aircraft components and the VHF, HF
or satellite communication systems.
The VHF communication system no.3, also called the center system, is
activated for voice communication.
ACARS operation is possible with VHF communication system no.3 if you can
read DATA or ACARS in the window of the active frequency. The ACARS MU
automatically selects the required VHF frequency, but does not display it on the
RMP.
ACARS uses the SATCOM or HF system if a VHF ground station is not usable.
This depends on the aircraft position which is provided by the flight
management computer system or IRS.
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Figure 35 ACARS Main Menue

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ACARS Operation cont.
ACARS gets maintenance related data from the central maintenance computer
and the aircraft condition monitoring system. In addition ACARS gets aircraft
status information from several discrete signals, for example door and gear
switches.
The software of the management unit can be updated with the data loader
when required.
ACARS operation is controlled from an MCDU and the printer allows the crew
to get a hardcopy of each report.
The ACARS main menu gives the operator access to different functions.
You can either request reports for an uplink or create reports for a downlink.
The available choices depend on the flight phase; in our example they are from
the pre−flight phase.
You can also write a telex to a ground station or request a voice contact from a
ground station.
Finally you can select a list of all uplink messages and get access to
miscellaneous pages.
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From the miscellaneous page you can select information about the ACARS
frequencies for the different areas of the world.
The OOOI-status pages give information about the OUT, OFF, ON and IN
downlinks and allows checking and editing of the status conditions.
The VHF and satellite statistic pages show how many transmissions and
receptions happened in the past and the parameter page gives access to
coded information.
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From the ACARS maintenance page you can select information about all part
numbers of the system, the ACARS system status and all information about
the status of the VHF and satellite communication system. Finally you can do
different types of system tests.
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07|SATCOM Intro/ALL
COMMUNICATIONS
DATA TRANSMISSION
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SATCOM INTRODUCTION
The satellite communication or SATCOM system has 3 main components. First
the satellites, secondly the aircraft earth stations, abbreviated as AES, and
finally the ground earth station, or GES.
The SATCOM system provides reliable worldwide digital data transfer for
ACARS, cockpit voice and telex communications and passengers voice, telex
and fax communications.
All communication systems can use SATCOM at the same time.
Transmission and reception also work at the same time so that normal
telephone conversation is possible.
SATCOM uses 4 satellites in a geostationary orbit, which means that they are
located about 23 000miles or 36 000km above the earth’s surface. This
provides a coverage between latitudes of 75° north and 75° south.
Over 255 SATCOM ground earth stations worldwide transmit and receive data
to and from the satellites.
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08|SATCOM Aircraft Comp/ALL
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DATA TRANSMISSION
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ATA 23
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SATCOM AIRCRAFT COMPONENTS
The aircraft earth station (AES) is the part of the SATCOM system which is
located onboard the aircraft. Its architecture depends on the system
manufacturer and the needs of the airline.
A typical system has a satellite data unit, or SDU in short, a radio frequency
unit, or RFU in short, a high power amplifier, called HPA in short, and a low
noise amplifier and diplexer, abbreviated to LNA / DIP.
Finally it has a beam steering unit, BSU in short, and an antenna.
The satellite data unit is the heart of the SATCOM system and controls all the
connections to other aircraft systems, for example ACARS, pilots audio system
and passenger telephone system.
It stores all satellite positions and frequencies and automatically selects the
nearest satellite depending on the present position of the aircraft.
Different functions and tests can be selected from the MCDU via the SATCOM
menu.
Let us now see briefly how a satellite communication is done. First the SDU
sends the communication data to the RFU. It generates a carrier frequency of
1.6GHz and modulates it with the data.
After amplification in the high power and low noise amplifiers the signal reaches
the BSU and the antenna.
The SATCOM system uses either 1 topmounted or 2 sidemounted antennas on
the upper part of the fuselage.
Both types are high gain antennas with several antenna elements. They
transmit a steerable beam in the direction of the satellite. The beam direction is
controlled by the BSU depending on the aircraft position and heading; therefore
the IRS must be functional if the antennas are to be used.
The high gain antennas allow high data transmission rates which is necessary
for normal SATCOM operation.
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Figure 40 SATCOM Aircraft Components 1

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SATCOM Aircraft Components cont.
Some systems also use a low gain antenna on top of the fuselage which
transmits a fixed beam. This allows only a low data rate communication, for
example for ACARS, but no voice communication. The advantage of this
antenna type is that it does not need a BSU nor aircraft position data from the
IRS.
Note that the concentrated beam of the SATCOM antennas is high powered so
SATCOM must only be used if no personnel or metal parts are near the
antenna. Refer to the maintenance manual for more detailed information.
A received signal goes from the antenna to the diplexer which separates the
transmission and reception signals.
From the diplexer the data goes via the RFU to the SDU where it is
demodulated and distributed to the related systems.
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Figure 41 SATCOM Aircraft Components 2

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10|ELT/ALL
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EMERGENCY LOCATOR TRANSMITTER (ELT)
Emergency locator transmitters, or ELTs in short, help search-and-rescue
crews to find aircraft that accidentally land away from an airport or ditch into
water.
Two different types of ELT are used in aircraft.
S The first type is a fixed transmitter which is installed in the upper aft section
of the aircraft fuselage.
S The second type is portable. It is either a buoyant type, which you can find
near the life rafts in the cabin ceiling or a handheld tranmitter as its modern
replacement.
All ELTs transmit 2 radio signals on international emergency frequencies.
One signal at the VHF frequency of 121.5MHz and the other at the UHF
frequency of 243MHz. Both radio signals are modulated with a swept−tone
signal.
UHF and VHF frequencies can only be received up to a distance of about
200nm, so a rescue crew can only find the aircraft if it is located inside this
range.
Therefore the fixed ELT transmits an additional signal at 406MHz via a small
antenna near the vertical stabilizer. This signal can be received by satellites
and allows worldwide location of aircraft. The signal contains information about
the aircraft type and tail-sign and if available also the last known present
position.
The ELTs are powered by an internal battery for at least 48 hours.
The buoyant type ELT becomes active when the battery comes in contact with
water or when a small pin is removed from the battery.
The fixed ELT is automatically activated when an internal g−switch detects an
acceleration of more than 5G in the longitudinal axis.
The fixed ELT can also be activated manually from a control panel on the
cockpit overhead panel.
All ELTs must never be switched on except in case of emergency because a
transmission will start search and rescue operations immediately.
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Fixed ELT activation switch
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Figure 42 Emergency Locator Transmitter

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01|Intro/ALL
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RADIO NAVIGATION
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RADIO NAVIGATION SYSTEM
INTRODUCTION
Radio navigation systems use the radio signals from ground stations to help
the pilot to navigate the aircraft.
Two systems are used for enroute navigation: First the ADF system which is
the oldest system. ADF stands for automatic direction finder.
Second the VOR system which is the most common system. VOR stands for
VHF omnidirectional range.
A third radio navigation system is the instrument landing system, or ILS in
short, which gives information to land the aircraft in poor visibility.
It has three subsystems:
S first the localizer
S second the glide slope
S and third the marker beacon.
A modern version of the instrument landing system is the microwave landing
system or MLS in short. It has some advantages over the ILS but, so far, it is
not in common use, so we will not discuss it here.
The ADF system has a receiver and antennas and often also a control panel. It
uses radio signals from ground stations to calculate the direction to the station.
This direction is indicated in the cockpit.
The VOR system has a receiver, an antenna and often also a nav control
panel. It uses radio signals from VOR ground stations to calculate the direction
to the station. This information is used for the autopilot and is indicated in the
cockpit.
The localizer system has a receiver, an antenna and often also a control panel.
It uses radio signals from a ground station to calculate the lateral guidance to
the runway centerline. This is used for the autopilot and for indication.
The glide slope system has a receiver and an antenna. It uses radio signals
from a ground station to calculate the descent path to the touchdown point on
the runway for the autopilot and for indication.
The marker beacon system has a receiver and an antenna. It supplies visual
and aural indications when the aircraft passes marker beacon transmitters in a
specific distance to the runway.
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Figure 43 Radio Navigation Systems

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02| NAV Charts/ALL
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NAVIGATION CHARTS
In this segment we will give you some general information about radio
navigation.
For this task we will use 2 different types of chart used by the pilots. First we
have a brief look at the ICAO chart. ICAO stands for International Civil Aviation
Organization.
Later we look at the enroute charts that are more commonly used on
commercial flights.
The ICAO chart is used for flying by both Visual Flight Rules and Instrument
Flight Rules.
Visual Flight Rules, or VFR in short, means flying in good weather conditions
and with visual ground references. This is only used by small private aircraft.
Instrument Flight Rules, or IFR in short, means flying without visual ground
references, day and night, or in bad weather conditions. These rules are used
by all commercial flights.
IFR flights need aid from radio navigation systems and their ground stations to
perform a safe and economic flight.
All types of ground stations have their own symbols on the chart. Adjacent to
the symbol is a text box, which contains the name of the station, the frequency
in megahertz and the ident in Morse code.
The ground station for the ADF system, called the non directional beacon or
NDB in short, has a different symbol but with a similar text box. Here the
frequency is given in KHz.
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Figure 44 ICAO Chart

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Navigation Charts cont.
This type of chart is used in commercial flights and is called enroute chart. It
shows all types of radio navigation aids and for example flight route lines. It
does not show objects on the ground like roads and so on.
The enroute chart has its own symbols but they are similar to those on the
ICAO chart.
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Figure 45 Enroute Chart

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04|Basic NAV/ALL
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BASICS OF NAVIGATION
There are some general items of navigation that we have to look at before we
go into the specific radio navigation systems.
The aircraft has 3 axes. When we speak about different directions it is the
longitudinal axis that is the reference.
You probably also remember from the compass system, that the earth has 2
north poles which unfortunately are not at the same location. One is the
geographical north pole and the direction to this pole is called true north or TN
in short.
The other is the magnetic north pole where the magnetic fieldlines are
gathering. The direction to this pole is called magnetic north or MN in short. In
our example the two directions are 10° apart.
This difference between true and magnetic north is called variation, or var in
short. It can be east or west.
The direction in which the nose of the aircraft is pointing is called heading, or
HDG in short, and is measured clockwise from north.
Because we have 2 north poles we must also have 2 headings dependent on
the reference. One is called true heading, or TH in short and the other
magnetic heading or MH.
This magnetic heading is indicated to the pilot on the compass rose behind the
lubber line, in our example 90°.
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Figure 46 General Items of Navigation

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Basics of Navigation cont.
Track, or TK in short, is the direction in which an aircraft is moving over the
earth. It is also measured from true or magnetic north.
If there is no wind the track and the heading are the same.
But if there is wind track is no more the same as heading.
The difference between the two angles is called drift.
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Figure 47 TK or Track

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Basics of Navigation cont.
Bearing, or BRG in short, is the direction from the aircraft position to an object,
for example a ground station.
It is called relative bearing, or RB in short, if the reference is the longitudinal
axis of the aircraft.
The relative bearing is measured in degrees clockwise from the longitudinal
axis. 0° means that the object is straight ahead of the aircraft.
True bearing, or TB in short, measures from true north and magnetic bearing,
or MB in short, measures from magnetic north.
You can calculate the magnetic bearing when you add the magnetic heading to
the relative bearing.
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Figure 48 Bearing or BRG

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07|Tuning/ALL
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NAVIGATION SYSTEM TUNING
A radio receiver in your home has to be tuned to the frequency of the
transmitter you want to listen to.
This is also true for the radio navigation receivers. In modern aircraft this can
be done in three different ways.
The normal way is the automatic tuning from the flight management system.
The second way is manual tuning via the FMS by selecting a frequency on the
nav radio page on the MCDU.
Finally manual tuning is always possible with a nav control panel or the radio
management panel as it is called in Airbus aircraft.
The automatic tuning by the FMS is based on the flight plan which the pilot
creates before the take-off.
If a waypoint during the flight is a radio navigation ground station, the frequency
is automatically selected and the navigation data is displayed.
As the flight progresses new stations are automatically tuned.
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Figure 49 Radio Navigation Receiver Tuning

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08|ADF Intro/ALL
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ADF INTRODUCTION
The automatic direction finder, ADF in short, is a radio navigation system that
receives radio signals in the frequency band of 190 to 1750khz from ground
stations.
The ADF receiver calculates the relative bearing and provides it to a radio
magnetic indicator, or RMI in short and to the navigation display.
The ADF system also provides an aural output to the aircraft audio system for
transmitter identification.
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Figure 50 ADF System

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ADF Introduction cont.
Three types of ground stations can be used for ADF navigation.
These are non directional beacons, or NDB in short, used for enroute
navigation and locators which are used for approaches.
These locators are often located with marker beacons, which belong to the
instrument landing system. Locators look similar to NDBs but have lower
output power and a smaller mast.
It is also possible to use public radio stations, if the position of the transmitting
antenna is known.
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Figure 51 Non Directional Beacon

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ADF COMPONENTS
A typical ADF system has a receiver which is located in the avionics
compartment and antennas which are located on the top of the fuselage, as in
this example, or at the bottom.
As you have seen already the receiver tuning is done either from the FMS or
from the relevant ADF control panel.
The relative bearing signal from the ADF receiver is presented on the
navigation displays and on most aircraft also on a radio magnetic indicator.
With the audio control panel the pilot can select the ADF system to hear the
identification.
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Figure 52 Typical ADF System

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ADF PRINCIPLE
The ADF system receives the electromagnetic waves from the ground station
with 2 antennas.
The loop antenna receives the magnetic part of the wave and delivers the
loop−signal to the ADF receiver.
The sense part of the ADF antenna receives the electric part of the wave and
delivers this as the SENSE signal to the ADF receiver.
The ADF receiver uses both signals to calculate a relative bearing signal and
positions the bearing pointers on the navigation display and the RMI.
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Figure 53 Relative Bearing Indication

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ADF ANTENNAS
You probably know already that turning this receiver type changes the
reception strength.
During a 360° turn you get two areas of minimum reception strength and two
maximums.
So with a loop antenna like in a home receiver you can find the direction to the
station.
A loop antenna receives the magnetic part of the electromagnetic wave. The
signal strength is at maximum when the coil axis is perpendicular to the
direction to the station and is at minimum when the axis is pointing to the
station.
In order to achieve the direction to the station you must turn the antenna back
and forth until you reach maximum signal strength or minimum signal strength.
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Figure 54 Loop Antenna

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ADF Antennas cont.
In the old days the loop antenna on aircraft looked like this and the navigator
turned the loop with a crank while listening to the station.
The loop was mechanically connected to a pointer on a compass rose where
the direction to the station could be read.
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Figure 55 Older Loop Antenna

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ADF Antennas cont.
As you probably noticed on the video of the loop antenna in the home radio
there are two maximums and two minimums of the signal strength.
This means that with the loop antenna alone the station could be in two
different directions.
This fact is also illustrated with this loop antenna pattern.
This ambiguity problem is removed by using a second antenna called sense
antenna. The sense antenna has a non directional pattern.
If you combine the signals from both antenna types you get a resulting cardioid
shaped pattern with a defined null in only one direction.
The direction to the station is now defined without ambiguity.
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Figure 56 Sense Antenna

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ADF Antennas cont.
The ADF antenna on modern aircraft has a fixed integrated design and has one
sense and two loop antennas.
The loops are not turnable but consist of two coils wound on a cross shaped
ferrite core. The ADF receiver combines the signals from the 2 coils to
calculate the direction to the station.
The sense antenna is a plate that forms a capacitance with the aircraft
structure.
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Figure 57 Modern ADF Antenna

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ADF CONTROL & INDICATION
The ADF System has 2 modes called ADF and antenna. In addition a BFO or
TONE function can be selected.
In the ADF mode the system is fully operational. It calculates the relative
bearing to the station and the station identifier in Morse code can be heard with
the audio system.
In the antenna, or ANT mode, only the sense antenna is active. Therefore you
do not get a relative bearing indication but the identifier is heard more clearly.
This mode is used when the station identifier reception is weak.
The BFO or TONE function is used if a ground station signal is not modulated
with a tone. They transmit the Morse code by interrupting the carrier wave. To
make the code audible, a beat frequency oscillator, BFO in short, inside the
receiver superimposes a tone on the received carrier wave so that the ident
can be heard.
In most modern glass cockpit aircraft the operation of the ADF is normally done
from the MCDU in conjunction with the flight management system.
As an alternate to the automatic tuning from the FMS you can select the
frequency on the NAV RADIO page. To select the ANT mode you must enter
the letter A after the frequency. If the BFO function is desired, enter the letter B
after the frequency.
To hear the ground station ident you must select ADF on the audio control
panel and set the volume control to a comfortable listening level.
The relative bearing to the ground station is presented on the navigation
displays and the radio magnetic indicator, or RMI in short.
If you have 2 ADF systems in the aircraft you can also find 2 pointers on the
navigation display. ADF 1 has a single line pointer and ADF 2 has a double line
pointer. The standard color for ADF is blue.
The pointer disappears if the reception of the tuned ground station signal is too
weak.
A Warning flag appears if a system failure is detected.
It is an amber box around the ADF text on the navigation display. Here a
warning flag is shown for ADF 2.
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Figure 58 ADF Modes

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ADF OPERATION
The EFIS control panel controls the navigation display in many ways.
Regarding ADF there are 2 switches. The left switch, called ADF−L, controls
the single pointer of the left ADF system which in other aircraft types is called
system no.1.
The other switch called ADF-R controls the double pointer of ADF no.2.
In the VOR position of the switch the bearing pointer is controlled by the VOR
system. In the off position the bearing pointers are erased from the navigation
display.
Bearing and heading information is presented on the RMI as well. Like the
Navigation Display the background compass card represents the aircraft
heading and the pointers show magnetic relative bearing to their respective
ground stations.
The RMI has 2 selector knobs which have the same function as the switches
on the EFIS control panel − they select either ADF or VOR.
As these pointers are always in view they move to the 3 o’clock position when
the signal from the tuned station is too weak, as you can see here for ADF 2.
You can also find ADF warning flags on the RMI and also a warning flag for the
compass system.
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Figure 59 EFIS Control Panel

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VOR INTRODUCTION
The VOR systems receive, decode and process bearing information from the
transmitted VOR signal.
VOR stands for VHF omnidirectional range, which means that it uses
frequencies in the VHF band and has both omni and directional transmitted
signals.
You can compare the VOR principle with a lighthouse. It has a rotating beam
and a flash light which you can see in all directions. It flashes when the rotating
beam points to magnetic north.
When you measure the time between the flash light and the visibility of the
rotating beam, you can identify the direction to the lighthouse.
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Figure 60 VOR Principle

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VOR Introduction cont.
The VOR ground station also transmits 2 signals. One is the reference signal,
transmitted in all directions, like the flash light of the lighthouse.
The second signal is called the variable signal which corresponds to the
rotating beam of the lighthouse.
Two types of ground stations are used, the conventional VOR, and the doppler
VOR. The doppler VOR is more expensive but has a better performance in
areas with a possibility of signal reflections, like near mountains or high
buildings.
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19|VOR Intro/ALL
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Figure 61 VOR Station Signals

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20|VOR Ind/ALL
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VOR INDICATIONS
The VOR receiver compares the 2 radio signals and, from the difference,
calculates the position of the aircraft relative to the VOR station.
This calculated position is called a radial which, in our example, is 240°.
Note that the radials correspond to the degrees of a compass rose so radial
zero points to magnetic north.
The indication on the radio magnetic indicator in the cockpit shows the radial
on which the aircraft is actually located with the aft end of the bearing pointer,
240° in our example.
This means that the bearing to the station is always the radial plus or minus
180°, in our example it is 60°.
Note that this bearing indication is independent of the heading of the aircraft.
The indication on the RMI is called the automatic VOR mode. It shows, in our
example, that the aircraft nose points to magnetic north − as you know this is
called the heading − and that the aircraft just passes the VOR radial 240, which
means that the station is in the 60° direction.
The actual track of the aircraft depends on the wind, so with the wind from west
it is for example 10° . This is not shown on the RMI.
The automatic VOR indication on the RMI is repeated on the Navigation
Display if the function is selected. You can see that the color for the VOR
indication is green.
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20|VOR Ind/ALL
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Figure 62 Automatic VOR Mode

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21|VOR Ind/ALL
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RADIO NAVIGATION
FUNDAMENTALS
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VOR Indications cont.
A second VOR indication on the navigation display requires a pilot action,
therefore it is called manual VOR mode.
It shows the difference between the radial the aircraft is actually located on and
a preselected radial. This difference is called VOR deviation and it is shown by
a moving deviation bar.
The selected radial is called the preselected course, or PSC in short, and is
either selected on the MCDU or on the autoflight control panel as you can see
here.
You will find a similar indication on the horizontal situation indicators, or HSI in
short, on aircraft without an EFIS.
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21|VOR Ind/ALL
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Figure 63 Manual VOR Mode

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22|VOR Ind/ALL
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RADIO NAVIGATION
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VOR Indications cont.
The indication on this navigation display shows us the following flight situation:
The aircraft has an actual heading of 273° and it is located on the radial 075 so
the bearing to the VOR station is 255°.
The preselected course, or PSC, is 225.
The deviation bar shows full right deflection when the difference between the
actual radial and the selected radial is 10° or more.
This means that one dot of deviation corresponds to a difference of 5° .
Here the difference is 30° because the PSC corresponds to a selected radial of
045 as long as we are flying to the station.
Additional VOR information on the Navigation Display includes station name
and TO or FROM text in the lower right part. Here TO is shown because we
are flying to the station.
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22|VOR Ind/ALL
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Figure 64 VOR Indications

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Page 130
23|VOR Comp/ALL
NAVIGATION
RADIO NAVIGATION
FUNDAMENTALS
ATA 34
HAM US/F-4 SaR 01.06.2007
VOR COMPONENTS
Commercial aircraft are equipped with 2 systems. Each system has a receiver
which is located in the avionics compartment and which is tuned either
automatically from the FMS or manually from the relevant NAV control panel.
The VOR system also has an antenna which is located on the vertical
stabilizer. You can either find it at the top, as in this example or on the side. If it
is on the side it is called a Flush−type antenna.
The outputs of the VOR receiver go, for display, to the navigation display or
HSI and on most aircraft also to a radio magnetic indicator.
Outputs are also provided to the autopilot and flight director of the autoflight
system and to the FMS for display on the MCDU and, in some systems, also
for position calculation.
The VOR Receiver has also an output to the audio system.
This allows identification of the VOR station by its Morse code.
In addition VOR stations at large airports also transmit spoken traffic
information and weather reports. This is called ATIS, which stands for
automatic terminal information service.
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23|VOR Comp/ALL
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Figure 65 VOR Systems

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Page 132
24|VOR Test/ALL
NAVIGATION
RADIO NAVIGATION
FUNDAMENTALS
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VOR TEST
Test can be performed in 3 different ways:
S operational test
S ground test
S and system test.
The operational test does not use external test equipment so it can be done by
the pilot or the mechanic.
To do an operational test you select a local VOR or test VOR station and check
that the indications on the navigation display and RMI are correct for the
situation. Then listen to the audio for the station ident or ATIS.
The ground test does not need external test equipment because the VOR
system in all modern aircraft has a built−in self test capability.
You can do the test in 2 different ways − either with the central maintenance
computer system via the MCDU or with a test switch on the VOR receiver in
the avionics compartment. The test result is shown by lamps on the receiver.
Only the system test uses a ramp test set to supply test signals.
You will find detailed instructions for all these tests in the Aircraft Maintenance
Manual.
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24|VOR Test/ALL
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Figure 66 VOR Test

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Page 134
25|ILS/ALL
NAVIGATION
RADIO NAVIGATION
FUNDAMENTALS
ATA 34
HAM US/F-4 SaR 01.06.2007
INSTRUMENT LANDING SYSTEM (ILS)
The instrument landing system, or ILS in short, provides lateral and vertical
position data necessary to put the aircraft on the runway for approach.
The system uses signals from a localizer and a glide slope transmitter on the
ground.
It provide outputs to the indicators for display and to the FMS and autoflight
system.
The system also has marker beacons, which we will talk about later.
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25|ILS/ALL
NAVIGATION
RADIO NAVIGATION
FUNDAMENTALS
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Figure 67 ILS System

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26|ILS LOC/ALL
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RADIO NAVIGATION
FUNDAMENTALS
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Instrument Landing System (ILS) cont.
The localizer, or LOC in short, ground station transmits 90Hz and 150Hz
signals for lateral guidance. These 2 signals are radiated to produce 2
directional lobes side by side along the runway centerline.
The left lobe is modulated with a 90Hz signal and the right lobe with 150Hz.
The Localizer ground station uses one of 40 channels in the 108.10 to
111.95MHz frequency range but uses only frequencies with odd tenths.
The transmitter is coupled to an array of directional antennas that radiate the 2
lobes along the runway centerline. The transmitter shed and the antennas are
located at the end of the runway.
An aircraft flying down the centerline would receive a signal with equal levels of
both modulations. This is shown by the centered deviation pointer on the
indicator, here the nav display.
If the aircraft position is left of the centerline, the 90Hz signal predominates
and the localizer deviation pointer deflects to the right, indicating that the
runway centerline is to the right.
One dot on the indicator normally shows a 1° offset on the localizer.
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26|ILS LOC/ALL
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Figure 68 LOC Signals

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Page 138
27|ILS GS/ALL
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RADIO NAVIGATION
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Instrument Landing System (ILS) cont.
The glide slope ground station transmits 2 lobes to give a descent path to the
touchdown point on the runway.
The upper lobe is modulated with 90Hz and the lower with 150Hz.
The centerline where both signals are equal has a slope of 2.5° to 3°.
The glide slope ground station uses one of 40 channels in the 329.15 to
335.00 MHz frequency range.
The transmitter uses a couple of directional antennas to radiate the two lobes.
The ground station is located beside the runway about 300 m beyond the
threshold.
When an aircraft flies on the glide slope centerline, the glideslope deviation
pointer on the navigation display is centered.
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27|ILS GS/ALL
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Figure 69 Glide Slope

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28|ILS Comp/ALL
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RADIO NAVIGATION
FUNDAMENTALS
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ILS COMPONENTS
Commercial aircraft have 2 or even 3 identical ILS installed. Each system has
the following main components:
S antennas
S receivers
S and the outputs to indicators and the autoflight system.
The localizer and glideslope antennas are usually located under the nose
radome.
Due to the different frequency ranges the localizer antenna is the larger and the
glideslope antenna the smaller one.
In some aircraft the VOR antenna is also used for the localizer system,
because of the same frequency range.
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28|ILS Comp/ALL
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Figure 70 ILS Components

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29|ILS Tuning/ALL
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RADIO NAVIGATION
FUNDAMENTALS
ATA 34
HAM US/F-4 SaR 01.06.2007
ILS TUNING
What you have learned already about receiver tuning is also true for the ILS
receiver, but with one difference. The ILS receiver has 2 receivers:
S one for localizer
S and one for glide slope.
On the approach chart you can only see information on the localizer frequency.
You see no information about the glide slope frequency.
But for each of the 40 localizer channels there is a paired glide slope channel
as shown in the table.
When the pilot selects an ILS frequency from the chart, the localizer receiver is
directly tuned.
In parallel the ILS frequency is translated to the paired glide slope frequency as
shown in the table and the glide slope receiver is automatically tuned to this
channel.
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29|ILS Tuning/ALL
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RADIO NAVIGATION
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Figure 71 ILS Receiver Tuning

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30|ILS Ind/ALL
NAVIGATION
RADIO NAVIGATION
FUNDAMENTALS
ATA 34
HAM US/F-4 SaR 01.06.2007
ILS INDICATIONS
ILS indications on modern aircraft are shown on the primary flight display and
on the navigation display as well.
ILS deviation output can also be displayed on mechanical indicators like this
standby attitude and ILS indicator and in older aircraft on the HSI and the ADI.
ILS displays on the PFD consist of the tuned frequency or the ground station
identifier if it is received.
The main ILS indications are the localizer and glideslope deviations.
Localizer deviation is normally displayed by a magenta diamond deviation
pointer on a white, four−dot deviation scale.
One dot equals about 1° of deviation from the runway centerline.
Under certain circumstances at the end of the approach, this display can
change to the expanded two−mark deviation scale. One dot now equals about
0.5° of deviation.
Glide slope deviation is displayed by a magenta diamond deviation pointer on a
white, four−dot deviation scale. One dot normally equals 0.35°. This
corresponds to 200 ft of deviation from the glide slope path at the outer marker.
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30|ILS Ind/ALL
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Figure 72 ILS Indications

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31|LDG CAT/ALL
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RADIO NAVIGATION
FUNDAMENTALS
ATA 34
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ILS Indications cont.
In addition to the indications the ILS provides the localizer and glideslope
deviation signals to the autoflight system.
With these 2 signals the autopilot can do an automatic approach and landing
by controlling the aircraft to fly on the beam center.
The autopilot does not need any visibility to do this but the pilot must monitor
the automatic landing and to do this needs to see the runway. How much
visibility the pilot needs depends primarily on the airport and aircraft equipment.
Three poor weather landing categories are defined:
S CAT 1 needs about 800m of the runway in sight, called runway visibility
range, or RVR in short, at a height of 200ft.
S CAT 2 requires about 400m runway visibility at a height of 100ft.
S CAT 3 needs less then 200m runway visibility at a height below100ft.
The exact values depend mainly on the runway and the aircraft type.
When the pilot does not have the runway in sight in the required length, he
must start a go around manoeuvre at the decision height. The decision height
is also called the minimum.
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31|LDG CAT/ALL
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Figure 73 Landing Categories

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32|Marker/ALL
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RADIO NAVIGATION
FUNDAMENTALS
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HAM US/F-4 SaR 01.06.2007
MARKER BEACON SYSTEM
The marker beacon system, or MB in short, also belongs to the instrument
landing system.
It supplies visual and aural indications when the aircraft flies over marker
beacon transmitters.
Originally 3 marker beacons were defined:
S the outer marker,
S the middle marker
S and the inner marker, but the inner marker is no longer in use.
All marker beacon transmitters use a frequency of 75 MHz.
The outer marker, or OM in short, is located about 7km from the runway.
The transmitted signal is modulated with a 400 Hz tone. It turns on the blue
lamp on the marker beacon panel and it can be heard with the characteristic
Morse code identifier of dashes.
The middle marker, or MM in short, is located about 1000 m from the runway.
The transmitted signal is modulated with a 1300 Hz tone which turns on the
amber lamp on the marker beacon panel and it can be heard with the
characteristic Morse code identifier of dots and dashes.
The aircraft’s height is normally 200 ft when passing the middle marker − this
corresponds to the CAT 1 minimum.
The inner marker, or IM in short, is located about 300 m from the runway.
The transmitted signal is modulated with a 3000 Hz tone which turns on the
white lamp on the marker beacon panel and it can be heard with the
characteristic Morse code identifier of dots.
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32|Marker/ALL
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Figure 74 Marker Beacon System

B1_M11.05.02_2008.11.27 Avionics Systems.pdf

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