DHC 8 -100

Chapter

23
COMMUNICATIONS
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 deHavilland Dash 8 100/300 23 - Communications
Table of Contents Operation . . . . . . . . . . . . . . . . . . . . 24
Normal Operation . . . . . . . . . . . . . . 24
COMMUNICATIONS . . . . . . . . . . . . . . . . . 6
Description. . . . . . . . . . . . . . . . . . . . . 6 PASSENGER ADDRESS AND ENTERTAINMENT
Communications Systems. . . . . . . . . . . . . 6 SYSTEM . . . . . . . . . . . . . . . . . . . . . . 28
VHF Communications System. . . . . . . . . 6 Description. . . . . . . . . . . . . . . . . . . . 28
Audio Integrating System. . . . . . . . . . . 6 Components. . . . . . . . . . . . . . . . . . . 28
Attendant’s Interphone System. . . . . . . . . 6 Cabin Interphone Control Unit . . . . . . . . 28
PA and Entertainment System . . . . . . . . . 8 Attendant’s Control Panel . . . . . . . . . . 28
Cockpit Voice Recorder System . . . . . . . . 8 Handset/Cradle Unit . . . . . . . . . . . . . 28
Attendant’s Annunciator Panel. . . . . . . . 30
VHF COMMUNICATIONS SYSTEM (KING) . . . . 10 Passenger Service Units (PSU). . . . . . . 30
Description. . . . . . . . . . . . . . . . . . . . 10 Power Supplies and Grounds . . . . . . . . 30
Components. . . . . . . . . . . . . . . . . . . 10 Operation . . . . . . . . . . . . . . . . . . . . 32
Antennas. . . . . . . . . . . . . . . . . . . 10 Flight Crew to Passengers Address . . . . . . . 32
Control Unit. . . . . . . . . . . . . . . . . . 10 Flight Attendant to Passengers Address. . . . . 32
Operation . . . . . . . . . . . . . . . . . . . . 12 Passengers to Flight Attendant Call . . . . . . . 34
Frequency Selection . . . . . . . . . . . . . 12 Mask Mic/Headphones. . . . . . . . . . . . . .34
Channel Mode . . . . . . . . . . . . . . . . 12 PA Audio Levels . . . . . . . . . . . . . . . . . 34
Program Mode . . . . . . . . . . . . . . . . 12 PA Emergency Power . . . . . . . . . . . . . . 34
Receive Mode. . . . . . . . . . . . . . . . 14 ‘No Smoking’ and ‘Fasten Seat Belts’ Warning . 38
Transmit Mode. . . . . . . . . . . . . . . . 14 System Lights. . . . . . . . . . . . . . . . . . 38
VHF COMMUNICATIONS SYSTEM (COLLINS) . . 16 PASSENGER BRIEFING SYSTEM (PBS-400) . . . 40
Description. . . . . . . . . . . . . . . . . . . . 16 General . . . . . . . . . . . . . . . . . . . . . 40
Components. . . . . . . . . . . . . . . . . . . 16 Description. . . . . . . . . . . . . . . . . . . . 40
Antennas. . . . . . . . . . . . . . . . . . . 16 Operation . . . . . . . . . . . . . . . . . . . . 40
Control Unit. . . . . . . . . . . . . . . . . . 16
Operation . . . . . . . . . . . . . . . . . . . . 16 AUDIO INTEGRATING SYSTEM . . . . . . . . . . 42
Description. . . . . . . . . . . . . . . . . . . . 42
UNIVERSAL UNILINK SYSTEM - UL-701 . . . . . 24 Components. . . . . . . . . . . . . . . . . . . 42
Description. . . . . . . . . . . . . . . . . . . . 24 Operation . . . . . . . . . . . . . . . . . . . . 42
Components . . . . . . . . . . . . . . . . . 24 Multiplexing. . . . . . . . . . . . . . . . . . 42
CDU - Flight Management Systems . . . . . 24 Modes of Operation . . . . . . . . . . . . . 44

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Communications Radio Transmission . . . . 44
Communications Radio Reception. . . . . . 44
Navigation Radio Reception . . . . . . . . . 46
Interphone. . . . . . . . . . . . . . . . . . 46
Emergency Operation. . . . . . . . . . . . 46
STATIC DISCHARGING (T.C.O. MFG. CORP.) . . 48
Description. . . . . . . . . . . . . . . . . . . . 48
Components. . . . . . . . . . . . . . . . . . . 48
Operation . . . . . . . . . . . . . . . . . . . . 48
STATIC DISCHARGING (CHELTON MINIPROBE) .50
Description. . . . . . . . . . . . . . . . . . . . 50
Component Details. . . . . . . . . . . . . . . .50
Operation . . . . . . . . . . . . . . . . . . . . 50
COCKPIT VOICE RECORDER SYSTEM (FAIRCHILD
FA2100CVR) . . . . . . . . . . . . . . . . . . . . 52
Description. . . . . . . . . . . . . . . . . . . . 52
Components . . . . . . . . . . . . . . . . . 52
Power Supplies and Grounds . . . . . . . . 52
Operation . . . . . . . . . . . . . . . . . . . . 52
System inputs and Recording. . . . . . . . 52
System Monitoring . . . . . . . . . . . . . . 54
Test. . . . . . . . . . . . . . . . . . . . . . 54
Recording Erase . . . . . . . . . . . . . . . 54
Underwater Locating Device. . . . . . . . . 54
DHC-300 Differences . . . . . . . . . . . . . . . . 60
Audio Integrating System . . . . . . . . . . . . . . 60
Audio Control panel. . . . . . . . . . . . . . . 60

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 deHavilland Dash 8 100/300 23 - Communications
List of Figures Figure 20 – Interphone/Emergency - ACP. . . . 47

COMMUNICATIONS STATIC DISCHARGING (T.C.O. MFG. CORP.)

Figure 1 – Communications . . . . . . . . . . . . 7 Figure 21 – Static Discharging - T.C.O . . . . . 49
Figure 2 – Center Console - Controls . . . . . . . 9 STATIC DISCHARGING (CHELTON MINIPROBE)
VHF COMMUNICATIONS SYSTEM (KING) Figure 22 – Static Discharging (Chelton) . . . . 51
Figure 3 – VHF COMM (King). . . . . . . . . . 11 COCKPIT VOICE RECORDER SYSTEM (FAIRCHILD
Figure 4 – VHF COMM Control (King). . . . . . 13 FA2100CVR)
Figure 5 – VHF COMM Block Diagram . . . . . 15 Figure 23 – SSCVR and Component Locations. 53
VHF COMMUNICATIONS SYSTEM (COLLINS) Figure 24 – SSCVR Block Diagram (1 of 2). . . 55
Figure 6 – VHF COMM (Collins). . . . . . . . . 17 Figure 25 – SSCVR Block Diagram (2 of 2). . . 57
Figure 7 – VHF COMM Control (Collins). . . . . 19 DHC-300 Differences
Figure 8 – VHF COMM Block Diagram (Collins). 21
Audio Integrating System
UNIVERSAL UNILINK SYSTEM - UL-701 Figure 26 – ACP Series 300.. . . . . . . . . . . 61
Figure 9 – Unilink 701 Component Location. . . 25
Figure 10 – ACARS - UNILINK 701 . . . . . . . 27
PASSENGER ADDRESS AND ENTERTAINMENT
SYSTEM
Figure 11 – PA Components. . . . . . . . . . . 29
Figure 12 – PA Amplifier . . . . . . . . . . . . . 31
Figure 13 – Passenger Address - Flight Crew. . 33
Figure 14 – Passenger Address - Cabin Crew. . 35
Figure 15 – PA Audio Gain, Mask/Mic, Emergency
Power . . . . . . . . . . . . . . . . . . . . . . 37
Figure 16 – No Smoking, Fasten Belts & Lighting.39
PASSENGER BRIEFING SYSTEM (PBS-400)
Figure 17 – PBS 4000. . . . . . . . . . . . . . 41
AUDIO INTEGRATING SYSTEM
Figure 18 – Audio Integrating . . . . . . . . . . 43
Figure 19 – Audio Control Panel. . . . . . . . . 45

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COMMUNICATIONS CAUTION: SOME COMMUNICATIONS SYSTEMS
MAY CONTAIN DEVICES OR
Description COMPONENTS WHICH ARE STATIC
The communications systems provide the facilities that SENSITIVE. THEY ARE IDENTIFIED
follows: AS SUCH BY THE MANUFACTURER
THROUGH THE USE OF STATIC
■■Air−to−air and air−to−ground communication in the AWARENESS LABELS.
VHF radio band
■■Flight crew interphone VHF Communications System
■■Flight crew/ground crew interphone The VHF communications system consists of two
■■Flight crew/flight attendant interphone independent and similar systems, each providing AM
voice communication (reception and transmission) in
■■Observer’s position to flight crew/ground crew the frequency 118.00 MHz through 135.975 MHz. Each
interphone system consists basically of a VHF transceiver and
■■Announcements to passengers by flight crew and control unit (VHF system No. 1 and No. 2).
flight attendant
Audio Integrating System
■■Passengers to flight attendant call
■■Flight crew monitoring of navigation radio audio The audio integrating system consists of a pilot’s system,
a copilot’s system, and an observer’s system, each
■■Recording of flight crew speech (aid to containing an audio control unit. The system provides
investigation in event of an accident) interphone communication to and from the positions
Communications Systems of pilot, copilot, flight observer and ground crew. Audio
inputs from the navigation radio receivers are applied to
The systems which provide communication facilities are the system for monitoring by the flight crew. The system
the VHF communications system, the audio integrating control units provide the means by which the flight crew
system, the attendant’s interphone system, the selects the VHF communications system, flight deck
passenger address and entertainment system, and the interphone or the navigation radio audio inputs. For
cockpit voice recorder system.
Attendant’s Interphone System
NOTE: In addition, this Chapter also contains
information on the aircraft static discharging The attendant’s interphone system is independent of the
system. passenger address and entertainment system, although
some components of the system are also used in the

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Figure 1 – Communications
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 deHavilland Dash 8 100/300 23 - Communications
passenger address and entertainment system. The
attendant’s interphone system provides private
communication between flight crew and flight attendant.
If the flight crew calls the flight attendant, the call audible
alert is applied over the passenger cabin loudspeakers.
If the flight attendant calls the flight crew, the call audible
alert is applied through the audio integrating system.
PA and Entertainment System
The passenger address and entertainment system
is independent of the interphone system, although
some components of the system are also used in the
attendant’s interphone system. The system is used
by either the flight crew or the flight attendant to make
announcements to the passengers.
NOTE: The flight crew may interrupt the flight
attendant’s passenger address system at any
time, to make an announcement.
The system permits a passenger to call the flight
attendant; this is done when the passenger presses his
call button to cause an audible alert tone to sound over
the cabin loudspeakers.
Cockpit Voice Recorder System
The solid state cockpit voice recorder (SSCVR) system
provides continuous four−channel recordings of all flight
crew communications and conversations during the time
the aircraft electrical system is powered. The system
recordings provide an aid in an investigation, should the
aircraft be involved in an accident.

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Figure 2 – Center Console - Controls

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 deHavilland Dash 8 100/300 23 - Communications
VHF COMMUNICATIONS SYSTEM pushbutton−type squelch override switch (labeled PUSH
− TST), light sensor and frequency selection controls.
(KING)
The upper half of the display window displays the
Description frequency to which the transceiver is tuned (active
The very high frequency (VHF) communications frequency) and the lower half of the display window
system provides air−to−air and air−to−ground labeled SBY (standby) displays the standby frequency.
amplitude−modulated (AM) voice communications in the The frequency selector control consists of two concentric
frequency range 118.000 MHz through 135.975 MHz, selectors. The outer (larger) knob selects the MHz
selectable in 25 or 50 KHz increments. An expanded portion of the SBY display in 1 MHz steps, and the inner
frequency version of the receiver−transmitter and control (smaller) knob selects the KHz portion of the SBY display
unit expands the range to 151.975 MHz. Two similar but in 50 KHz steps (when pressed in) or in 25 KHz steps
separate VHF communications systems are installed; (when pulled out). The transfer switch (when pressed)
they are designated No. 1 and No. 2. transfers the displayed SBY to the ‘active’ frequency
Components display position. Frequency selection is made by
selecting the frequency manually,
The VHF communications system consists of the
communications (COMM) control unit No. 1, receiver/ Above the transfer switch is a light sensor. The light
transmitter No. 1. COMM control unit No. 2 and receiver/ sensor is a photo−cell which senses ambient light, and
transmitter No. 2. In addition, two VHF communications then automatically adjusts the display intensity.
antennas are provided, one for the No. 1 system and the The CHAN (channel) pushbutton provides the selection
other for No. 2 system. of channel mode, program mode, and the recall of
Antennas programmed frequencies by channel number.

The antenna for each VHF communications system is a The PUSH TST switch will alternately enable and disable
vertically−polarized type; impedance is 50 ohms nominal. the squelch circuit when pressed. The squelch circuit
in the receiver provides noise quieting in the absence
Control Unit of a received signal. With the receiver in this state of
The No. 1 COMM control unit and the No. 2 COMM operation, the PUSH TST is pressed once to permit noise
control unit are identical. The front panel of each control pickup (squelch disabled) needed to set receiver volume
unit (labeled COMM), contains a display window, level. Pressing PUSH TST a second time returns the
‘transfer’ switch, a pushbutton switch labeled CHAN, a receiver to the quiet state.

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Figure 3 – VHF COMM (King)

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 deHavilland Dash 8 100/300 23 - Communications
Operation channel frequency is placed in the standby window.
Pressing the CHAN button before the five second delay is
The VHF communications systems No. 1 and No. 2 are completed will return the unit to frequency mode, and the
similar, therefore only the operation of the No. 1 system status of frequency mode prior to entering channel mode
is described. Each system has two modes of operation; remains the same.
receive and transmit modes.
When in channel mode, pressing the transfer button will
Frequency Selection return the unit to frequency mode. The channel frequency
Manual frequency selection is provided by means of the will become the new active frequency, and the last active
MHz selector and the 25/50 KHz selector on the control frequency becomes the new standby frequency. If the
unit. To tune the transceiver to a new frequency, the unit was in active entry mode prior to entering channel
desired frequency must first be entered into the SBY mode, pressing the transfer button or allowing the unit to
(standby) display and then the transfer pushbutton must time out will bring it back to standby entry.
be pressed. This action transfers the contents of the SBY Program Mode
display to the ‘active’ display. The transceiver is always
tuned to the frequency appearing in the ‘active’ display. Program mode is selected by pressing and holding the
It is therefore possible to have two frequencies available, CHAN button for longer than two seconds. The unit
one in use (active) and one on SBY (standby). tunes the KTR−908 to the last active frequency displayed
before entering program mode, and the last used channel
Channel Mode number is displayed when program mode is entered.
Momentarily pressing the CHAN (channel) button while The channel number flashes, and turning either tuning
in frequency mode puts the unit in channel mode. The knob changes the channel number. When the channel
unit remains tuned to the last active frequency displayed number is flashing, pressing the transfer button will
before entering channel mode. The last−used channel cause the channel number to stop flashing, and cause
number is displayed unless no channels have been the frequency to flash. The tuning knobs then work as in
programmed, in which case the unit defaults to channel 1 frequency mode, except between rollover points 118.00
and dashes are displayed in the standby window. to 135.95 and 135.95 to 118.00, dashes are displayed
to de−program the channel. When frequency is flashing,
Tuning either tuning knob changes number and pressing the transfer button will cause the frequency to
corresponding frequency. The channels will only stop flashing, and the channel number to flash.
increment and decrement to channels that have been
programmed. If there has been no activity for five If no activity has occurred for 20 seconds, the unit returns
seconds the unit will return to frequency mode, and the to frequency mode. The unit can also be returned to

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Figure 4 – VHF COMM Control (King)

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 deHavilland Dash 8 100/300 23 - Communications
frequency mode from program mode by pressing the transmitter applies sidetone audio to the audio control
CHAN button. Returning to frequency mode will not units.
change the active or standby frequencies from what they
were prior to entering program mode.
Receive Mode
The synthesizer and receiver sections of the transceiver
are used in the receive mode. Frequency selection
information from the control unit is applied to the
synthesizer section. Signals from the synthesizer cause
the receiver section to tune automatically to the selected
frequency, which produces the audio output. The audio
output is applied to the audio control panels. Volume
of the receiver audio output is controlled at each audio
control panel. The receiver contains a squelch circuit for
noise−quieting during the absence of a received signal.
Transmit Mode
The synthesizer and transmitter sections of the
transceiver are used in the transmit mode. When the
microphone press−to−transmit (PTT) switch is operated
the receiver section of the transceiver is disabled, and
the transmitter section is activated. Frequency selection
control information from the control unit is applied to
the synthesizer section, which causes the transmitter
circuits to tune automatically to the selected frequency.
Microphone audio is applied to the transmitter section,
which produces an amplitude−modulated RF output.
The RF output is switched automatically to the antenna
and is blocked from the receiver section. During the
transmission, a ‘T’ appears in the display window to
indicate that the transceiver is in the transmit mode. The

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Figure 5 – VHF COMM Block Diagram

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 deHavilland Dash 8 100/300 23 - Communications
VHF COMMUNICATIONS SYSTEM off), pushbutton switches identified TEST, STO (store),
ACT (active) and an automatic display dimming sensor.
(COLLINS) The upper half of the front panel of each control unit
Description contains a display window, XFR/MEM (transfer/memory)
recall toggle switch, and annunciators which come on to
The very high frequency (VHF) communications annunciate MEM (memory), ACT (active frequency), TX
system provides air−to−air and air−to−ground (transmit) and RMT (remote). The RMT annunciator is not
amplitude−modulated (AM) voice communications in the used.
frequency range 118.000 MHz through 135.975 MHz,
selectable in 25 or 50 KHz increments. An internal jumper Operation
in the receiver−transmitter may be removed to extend
The VHF communications systems No. 1 and No. 2 are
the frequency range to 136.975 MHz. Two similar but
similar, therefore only the operation of the No. 1 system
separate VHF communications systems are installed;
is described. The operation and functions of the controls
they are designated No. 1 and No. 2.
and displays of the system are as follows:
Components Power/Mode Switch
The VHF communications system consists of the The power/mode switch provides selection of power
communications (COM) control unit No. 1, receiver/ ON−OFF and SQ OFF (squelch off). In the SQ OFF
transmitter No. 1, COM control unit No. 2 and receiver/ position the automatic receiver squelch circuit is
transmitter No. 2. In addition, two VHF communications disabled, to provide receiver noise for setting the
antennas are provided, one for the No. 1 system and the receiver audio output level. Volume is set on the
other for No. 2 system. associated audio control panel. The ON position
Antennas provides automatic squelch operation in addition to
system power on.
The antenna for each VHF communications system is a
vertically−polarized type; impedance is 50 ohms nominal Frequency Display

Control Unit When the system is switched on, two frequencies are
normally always being displayed. The top frequency,
The No. 1 COM control unit and the No. 2 COM control called the active (ACT) frequency, is the frequency to
unit are identical. The lower half of the front panel of which the transceiver is tuned. The bottom frequency
each control unit (labeled COM) contains the frequency displayed is called the preset frequency. These
selection controls, power/mode rotary selection switch two frequencies would be the same frequencies
with positions identified OFF, ON, SQ OFF (squelch

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Figure 6 – VHF COMM (Collins)

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that were present when the equipment was last the desired frequency is selected into the preset
switched off. The preset frequency is normally set for frequency display the STO pushbutton is then
convenience of having a second frequency that can pressed. The active display area now displays
be quickly transferred to become the active frequency. the available memory space (channel number)
A new active frequency may be selected directly designated CH 1 through CH 6; the preset
by means of the frequency selector knobs. This is frequency displays the frequency to be stored. For
done by pressing the ACT (active) pushbutton for approximately five seconds the MEM position of the
approximately two seconds, and selecting the desired XFR/MEM switch may be repeatedly selected to
frequency by operation of the selector knobs. The advance through the channel numbers, to reach the
ACT (active) annunciator, located at the left side of the desired channel for storing the preset frequency. The
active display, comes on and flashes when the active selected frequency does not change as the channel
frequency is being changed. If the ACT annunciator numbers are selected. The STO pushbutton is now
continues flashing after the active frequency has been pressed again to commit the preset frequency to
selected, it indicates that the transceiver is not tuned memory in the selected memory position (channel
to the frequency displayed in the active display. number). After five seconds, the controller will return
to normal operation.
ACT Pushbutton
XFR/MEM Recall Switch
The ACT (active) pushbutton (when pressed in for
approximately two seconds) enables direct frequency The XFR/MEM (transfer/memory) recall switch is a
selection by means of the frequency selector knobs. three−position spring−loaded toggle switch. Setting
The preset display will display dashes and the upper this switch momentarily to the XFR position will
window will continue to display the active frequency. cause the active and preset frequency displays to
Pressing the ACT pushbutton again returns the trade places, and the transceiver to retune to the
controller to the normal display mode. The ACT new frequency. When the switch is set or pushed
annunciator at the left side of the active display momentarily to the MEM position, one of the six
flashes when the active frequency is being changed. memory channel frequencies is displayed in the
preset frequency display. Successive pushes select
STO Pushbutton
the next memory channel frequency into the preset
The STO (store) pushbutton switch allows up to frequency display. The MEM annunciator comes on to
six frequencies to be selected and entered into annunciate that a stored frequency (channel) is being
the controller memory. The memory retains the displayed in the preselect frequency window.
frequencies even if the system is turned off. After

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Figure 7 – VHF COMM Control (Collins)

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Frequency Selection a timer in the transceiver is started, to terminate the
transmission in an elapsed time of two minutes. The
Frequency selection is necessary when a desired
timer is reset each time the PTT switch is released
frequency is not in the preset or memory channels.
and the line successfully opens. This feature protects
Frequency selection is made by operating the
the transmitter, and also frees the communication
frequency selection controls which consist of two
frequency from long−term interference. The
concentric selectors. The ACT pushbutton must be
overtemperature protection feature shuts down the
pressed before the frequency selection controls are
transmitter if its temperature exceeds 160 degrees
effective, and is used to select the desired frequency
C (320 degrees F). When this occurs, the transmitter
which appears in the active display. The larger
will not respond to a normal operation of the
(outer) knob changes the MHz portion of the display
microphone button. This feature may be overridden (if
(three digits to the left of the decimal point) in 1 MHz
a transmission must be made) by rapidly pressing the
increments. The smaller (inner) knob changes the
microphone button twice, and then holding it on the
KHz portion of the display (two digits to the right of
second press.
the decimal point) in 50 KHz increments (or in 25 KHz
increments for the first two steps after the direction of Receive Mode
rotation has been reversed). Numbers roll over at the
The synthesizer and receiver sections of the
upper and lower limits.
transceiver are used in the receive mode. Frequency
TEST Pushbutton selection information from the control unit is applied to
the synthesizer section. Signals from the synthesizer
When the TEST pushbutton is pressed, it initiates
cause the receiver section to tune automatically to the
a self−test diagnostic routine, and the transceiver
selected frequency. The RF signal from the antenna
performs a complete self−test requiring about five
is fed to the receiver section, which produces the
seconds.
audio output. The audio output is applied to the audio
Protection Features control panels. Volume of the receiver audio output is
controlled at each audio control panel. The receiver
The VHF controllers incorporate a stuck microphone
contains a squelch circuit for noise−quieting during
button protection feature, and an overtemperature
the absence of a received signal.
protection feature. The stuck microphone button
protection feature automatically terminates
a transmission (reverts to receive mode) if a
transmission lasts longer than two minutes. When the
press−to−talk switch is operated in VHF selection,

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Figure 8 – VHF COMM Block Diagram (Collins)

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Transmit Mode
The synthesizer and transmitter sections of the
transceiver are used in transmit mode. When the
microphone press−to−transmit (PTT) switch is
operated ( the receiver section of the transceiver
is disabled and the transmitter section is activated.
Frequency selection control information from the
control unit is applied to the synthesizer section,
which causes the transmitter circuits to tune
automatically to the selected frequency. Microphone
audio is applied to the transmitter section, which
produces an amplitude−modulated RF output. The
RF output is switched automatically to the antenna,
and is blocked from the receiver section. During the
transmission, TX appears in the display window to
indicate that the transceiver is in transmit mode of
operation. The transmitter applies sidetone audio to
the audio control units.

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UNIVERSAL UNILINK SYSTEM - UL-701 CDU - Flight Management Systems

Description The Unilink System is controlled from the Computer

Display Units of the Flight Management Systems. Refer
The Unilink System (ULS) installed in this airframe, which to the appropriate maintenance manual of the Flight
is integrated with the existing aircraft UNS-1E Flight Management System for the detail operation and testing
Management System, will provide the cockpit flight crew procedures.
the two-way communication capability with the selected
ground-based data service provider (DSP), allowing Operation
the upload and display of text, such as flight plan, pre- Universal Unilink System is a two-way data link for
departure clearance, SIGMET advisories, messages, air-to-ground communication which allows the aircraft
automatic position reporting, text weather, ETA updates, to connect to a ground data service provider (DSP).
digital ATIS, and more. For airline operators, the ULS is This Unilink System (ULS) uses the embedded VHF
fully ACARS compatible, supporting all ACARS message radio to communicate with the ground station, and all
types, including triggered events such as OOOI (Out, Off, control functions for the Unilink System is carried out by
On, In) times. Communication is carried out by its internal using the Computer/Display Unit of the Universal UNS-
VHF equipment via dedicated antenna. 1E Flight Management Systems. A thermal printer is
Components installed at the flight deck aft centre console to print out
any messages received by the Unilink System, when
■■Unilink Unit (UL-701)
required.
■■Thermal Printer (TP4429)
Normal Operation
■■VHF Antenna
ULS and VHF ACARS networks support Category A
The Unilink System is integrated with the following
operation, The ULS internal VHF radio will accept the
airframe systems:
autotune message from the ground station and as
■■Flight Management System(s) Universal UNS-1E a result tunes the radio to the requested frequency.
Normal system control is carried out by using the ACARS uplink messages are generated by Airline
Computer Display Units (CDU) of the Flight Management Ground Host Centres. ULS determines if the message
Systems. is addressed to the aircraft. If so, it generates a positive
acknowledgement for transmission to the ground station.
If the unlink message contains an error, ULS generates
a negative technical acknowledge to the ground station,
which will retransmit the uplink message. ULS downlink

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Figure 9 – Unilink 701 Component Location

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 deHavilland Dash 8 100/300 23 - Communications
messages can be generated by either the flight crew via
the user interface (FMS keyboard and display), or as a
response to an event having occurred, such as weight off
wheels.
Once a downlink message is encoded, it is queued
until the message can be transmitted to the ground
station. ULS is capable of queueing at least 70 blocks
of downlink messages. The downlink message will be
transmitted by its internal VHF radio only when ULS
has determined that the channel is clear. The downlink
messages will be transmitted according to their priority,
and the oldest from the same priority will be selected.
ULS completes transmission of a message block prior
to transmitting another message block. Upon receipt of
the downlink message, the DSP performs a BCS error
check and, if the message is error-free, routes it to the
proper destination. The ground station will generate a
positive technical acknowledgement for the message
to the aircraft. Upon receipt of this acknowledgement
for successful transmission by the ULS, the message is
deleted from the downlink queue.

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 deHavilland Dash 8 100/300 23 - Communications

Figure 10 – ACARS - UNILINK 701

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PASSENGER ADDRESS AND Attendant’s Control Panel
ENTERTAINMENT SYSTEM The attendant’s control panel contains pushbutton
switch−indicators identified PA, CALL and EMER. The
Description EMER switch−indicator is guarded. The attendant’s
The passenger address system provides the following: control panel also contains a rocker switch, identified
BOARD’G LIGHTS.
■■Flight crew to passengers address.
■■Flight attendant to passengers address. Handset/Cradle Unit
■■Passengers to flight attendant call. Each handset/cradle unit is comprised of a handset
■■‘No smoking’ and ‘Fasten Seat Belts’ warning assembly and cradle assembly. The handset assembly
chimes. contains a noise−cancelling microphone, an earphone
and a PUSH−TO−TALK switch. Audio amplification
In addition, provision is made for a passenger circuits required for the handset are located in the
announcement and boarding music input. cradle assembly. The flight crew unit has higher audio
Components amplification than the attendants unit. The cradle
assembly provides a seat for the handset when not
The passenger address system consists of the CABIN in use. The handset of the flight crew unit is retained
INTERPHONE control unit and attendant’s control panel, magnetically in the cradle assembly, while the handset
flight crew handset/cradle, attendant’s handset/cradle, of the attendant’s unit when fully seated in the cradle
attendant’s annunciator panel, PA (passenger address) assembly is lever locked in position. The lever, marked
amplifier with externally preset PA VOL (volume) − SENS PULL on attendant’s unit, has to be pulled down to
(sensitivity) controls, cabin speakers, lavatory speaker, release the handset for removal from the cradle. In
lavatory service call pushbutton, and passenger service attendant’s unit, a ‘hook’ switch provides handset ‘on
units (PSU). The system also utilizes circuits of the hook’ or ‘off hook’ status while in TIB DH8-23-04 flight
REU (remote electronics unit) which is shared by other crew unit, a magnetic switch in the cradle provides
communications systems. handset ‘on hook’ or ‘off hook’ status. The cradle
Cabin Interphone Control Unit assembly also contains a removable electronics module,
comprised of two printed circuit boards: one containing
The CABIN INTERPHONE control unit contains the audio circuits and power supply, and the other
pushbutton switch−indicators identified PA (passenger containing the signalling logic.
address), CALL, EMER (emergency, and an additional
pushbutton switch identified CHIME.

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Figure 11 – PA Components
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 deHavilland Dash 8 100/300 23 - Communications
Attendant’s Annunciator Panel symbol. The PSU also contains reading lights and
passenger air vent.
The attendant’s annunciator panel contains six colored
lights. Four of the lights provide the following alerts: The Power Supplies and Grounds
green light, when on, indicates that a passenger address
In normal operation power is obtained from the 28 volts
announcement is in progress. The amber light, when on,
dc left essential bus through the PA CAB INTPH PWR
indicates a service call from the lavatory. The blue light,
(M1) circuit breaker and normally−closed contacts of
when on, indicates a call from a passenger. The pink light
relay 3351−K2.
is not part of the passenger address and entertainment
system, but part of the CABIN INTERPHONE system. Failure of the essential bus activates the emergency
The red light is used in conjunction with the lavatory lights power supply unit PS1. This energizes relay
smoke detector system. 3351−K2 to supply 28 VDC from the right battery bus
through the PA EMER PWR (J1) circuit breaker to the PA
P.A. Amplifier
amplifier.
The PA amplifier provides the audio amplification required
for:
■■Flight crew to passengers address.
■■Flight attendant to passengers address.
■■Recorded announcements.
■■Recorded music.
■■Chimes
External controls, identified PA VOL (volume) and SENS
(sensitivity) are provided for adjustment of cabin speaker
output level and microphone input sensitivity respectively.
Passenger Service Units (PSU)
Each PSU contains the following components associated
with the PA (passenger address) system: passenger to
attendant (touch−type) call switch; attendant call light
(blue); ‘No Smoking’ and ‘Fasten Seat Belts’ warning

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Figure 12 – PA Amplifier
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 deHavilland Dash 8 100/300 23 - Communications
Operation The red light is associated with the LAVATORY SMOKE
DETECTION SYSTEM
The passenger address system is controlled from the
cabin interphone control unit or the attendant’s control Flight Crew to Passengers Address
panel. The PA electronics unit contains circuits which
A flight crew member makes an announcement on the
interface and control the cabin interphone control unit
PA system by first selecting PA on either audio control
and the attendant’s control panel. The PA electronics unit
panel and then pressing the PA switchlight on the cabin
also provides +15v dc power supply for the attendant’s
interphone control unit. This causes the green PA lights
handset and cradle assembly circuits. The control and
on the cabin interphone control, attendant’s control and
interfacing function is initiated when the attendant’s
the annunciator panel to come on. The green light on
handset is removed from its cradle, or the (optional) hand
the attendant’s annunciator and control panel alerts the
microphone is used, and a switchlight on the control is
attendant that the PA system has been selected. The
switched on. A voltage discrete signal (v sel) is fed to
flight crew member then presses the press−to−talk (PTT)
the PA electronics unit from the cradle assembly circuits.
switch and uses the hand or boom microphone to make
This signal identifies the function selected at the control
the announcement over the cabin speakers. When the
panel. The PA electronics unit applies a ground to the
announcement is concluded, the flight crew member
appropriate switchlight in all control units to turn on the
cancels PA on the cabin interphone control unit by
switchlights. The PA electronics unit prioritizes passenger
pressing the switchlight again. All PA lights go off.
address such that the flight crew has priority over the
attendant. The passenger address system may be used Flight Attendant to Passengers Address
by a passenger to call the flight attendant by operation
of the call switch on any of the PSUs, or by operation of The flight attendant makes an announcement on the PA
the service call pushbutton located in the lavatory. The system by removing the handset from the cradle, and
attendant’s annunciator panel contains six colored lights. then pressing the PA switchlight on the attendant’s control
Four of the lights provide the following alerts: panel. This causes the PA light (green) on the attendant
control and annunciator panel, and the cabin interphone
■■Green − PA in use.
control unit to come on.
■■Pink − Call (normal or emergency) from flight crew
(not part of passenger address and entertainment NOTE: The flight crew has PA selection priority over
system). the attendant’s PA selection at any time.
■■Blue − Call from passenger. The PA light on the cabin interphone control unit alerts
■■Amber − Call from lavatory. the flight crew that the passenger address system
has been selected for use by the flight attendant. The

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Figure 13 – Passenger Address - Flight Crew

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 deHavilland Dash 8 100/300 23 - Communications
attendant presses the press−to−talk switch on the Mask Mic/Headphones
handset and then speaks into the handset mic and the
announcement is heard on the cabin speakers. On The pilot’s mask microphone and headphones are
conclusion, the attendant replaces the handset in the automatically enabled when MASK is selected on the
cradle, or cancels the PA on the attendant control panel pilot’s audio control panel, and one of the three modes of
by pressing the PA switchlight again. the passenger address system (PA, CALL and EMER) is
selected on the cabin interphone control unit. In the PA
Passengers to Flight Attendant Call mode the pilot or the copilot uses the INPH position on
the INPH/PTT switch on the control column handwheel.
A passenger to flight attendant call is made by the
The mode is cancelled by pressing the PA switchlight a
passenger touching the passenger to attendant call
second time.
switch, on the center of the PSU (passenger service unit).
A PSU is located overhead each pair of passenger seats. PA Audio Levels
When the passenger to attendant call switch is touched,
it causes the blue light on the PSU to come on, the blue Two audio levels are provided by the PA system; a 6 dB
light on the attendant annunciator panel to come on, attenuated level and an unattenuated level. The 6 dB
and a single HI chime to sound on the cabin speakers. attenuation is applied through energized contacts of relay
The attendant is thereby alerted of a passenger call 2912−K3. When engine No. 2 is started and oil pressure
both visually and aurally. The attendant responds to increases above 60 psi, the oil pressure switch removes
the passenger call and then resets the system by the ground from relay 2912−K3 to de−energize the relay,
touching the passenger to attendant call light on the PSU which in turn removes the 6 dB attenuation from the PA
originating the call. This action causes the blue light on system.
the PSU, and the blue light on the attendant annunciator PA Emergency Power
panel to go off. A passenger to attendant (service call)
switch is located in the lavatory compartment. When the The passenger address and entertainment system is
service call switch is pressed, a single HI chime sounds normally supplied with 28 vdc from the left essential
on the cabin speakers, and the amber light (service call bus, through the PA CAB INTPH PWR circuit breaker
lavatory) on the attendant’s annunciator panel comes (M1) on the left dc circuit breaker panel and through the
on to alert the attendant that assistance is needed in the normally−closed contacts of deenergized relay 3351−K2.
lavatory. The attendant responds to the call and resets In event of a power failure, or for any other reason the
the system by pressing the service call pushbutton. emergency lights are triggered on, 3351−K2 is energized
This action causes the amber light on the attendant’s from the emergency lights power supply (PS1). The PA
annunciator panel to go off. system is thereby supplied from the 28 vdc right battery

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 deHavilland Dash 8 100/300 23 - Communications

Figure 14 – Passenger Address - Cabin Crew

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 deHavilland Dash 8 100/300 23 - Communications
THIS PAGE INTENTIONALLY LEFT BLANK

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Figure 15 – PA Audio Gain, Mask/Mic, Emergency Power

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 deHavilland Dash 8 100/300 23 - Communications
bus through the PA EMER PWR circuit breaker (J1) on
the right dc circuit breaker panel, and the energized relay
3351−K2. For additional information on the emergency
lights power supply and relay 3351−K2.

‘No Smoking’ and ‘Fasten Seat Belts’ Warning

When the NO SMOKING switch (S1) and FASTEN
BELTS switch (S2) on the flight compartment overhead
panel are closed, 28 vdc is applied to the PA amplifier
and to the ‘no smoking’ and ‘fasten seat belts’ symbol
lights on the PSUs. This causes a single LO Chime to
sound on the cabin and lavatory speakers, and the ‘no
smoking’ and ‘fasten seat belts’ symbols lights to come
on.
System Lights
The ATT, CALL, PA and EMER switchlights on the flight
crew cabin interphone control unit are provided with
5 vdc and 28 vdc power supplies. The 5 vdc supply
is continuous and provides ambient lighting for the
switchlight legends. The 5 vdc supply is applied through
a dimming control on the flight compartment overhead
console). When a switch/light is selected on, the 28 vdc
supply provides increased illumination of the switchlight
legend. The 28 vdc supply is controlled through dimming
and test circuits in the AFCS (automatic flight control
system) interface unit. The EMER, PA, CALL and
ATT switchlights on the attendant’s control panel are
provided with 28 vdc (non−dimmable) power from the left
essential bus (normal operation) or the right battery bus
(emergency operation) through relay 3351−K2.

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 deHavilland Dash 8 100/300 23 - Communications

Figure 16 – No Smoking, Fasten Belts & Lighting

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 deHavilland Dash 8 100/300 23 - Communications
PASSENGER BRIEFING SYSTEM (PBS-
400)
General
The PBS400 Digital Passenger Briefing system
enables the Cabin crew to initiate pre-recorded cabin
announcements. These announcements can be made in
four languages.

Description
The Digital Passenger Briefing system is comprised of a
remote computer unit and a control unit. The control unit
is mounted in the area immediately above the wardrobe
closet. The remote computer is mounted to the ceiling of
the wardrobe just behind the control unit. Electrical power
for the Briefing system is supplied from the 28 V DC bus
1 via a circuit breaker labelled as "PASS BRIEF" and
located at (L5) in the electronics circuit breaker panel.
Provision for updating the audio in the remote computer,
is accomplished via a 25 contact connector on the unit.

Operation
The PBS400 computer memory is programmed to store
Digital audio information. To play the message, the
PBS400 computer recalls the message from memory,
translates the digital information into "recordertype"
electrical signals, and sends these signals to the existing
Aircraft Public address audio system (P.A.Amplifier). The
PBS400 has a self test feature that is activated during its
power up

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 deHavilland Dash 8 100/300 23 - Communications

Figure 17 – PBS 4000

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 deHavilland Dash 8 100/300 23 - Communications
AUDIO INTEGRATING SYSTEM of the audio integrating system, called the Remote
Electronics Unit (REU), located in the Avionics rack. The
Description audio control panel is the principal component of each
The audio integrating system provides the pilot, copilot station. Each audio control panel contains a rotary−type
and observer with the means to control the aircraft MIC (microphone) transmission selector switch, which
communications radio systems for transmission provides the selection of VHF 1, VHF 2, INT (interphone)
and reception, and to monitor the aircraft navigation and (when installed) HF, UHF and FM communications
receivers. In addition, the system provides interphone systems. The audio control panel also contains twelve
communications from pilot to copilot, flight crew to ground (push−on/push−off/turn volume control) receiver selector
crew, and from the observer’s position to flight crew and switches, and two additional switches of the same type
ground crew. for SPKR/VOL (speaker/volume) and SERV/INT (service/
interphone). In addition, the panel contains a lever−lock
Components type MIC (microphone) selector switch, which provides
for the selection of BOOM or MASK (oxygen mask
The audio integrating system consists of three similar
microphone), and a switch of the same type for selection
control stations; pilot’s, copilot’s, and observer’s stations.
of NORM/EMER (normal or emergency) operation.
The pilot’s and copilot’s stations are each made up of
By a multiplexing system, operation of the controls
an audio control panel located on the center console,
and switches on the audio control panels control the
hand microphone, jack panel, cockpit speaker and
functioning of the remote electronics unit, to which all the
press−to−talk/interphone (PTT/INPH) switch An
communications and navigation systems audio outputs
additional press−to−talk switch, labelled PTT, is provided
are connected, and through which all audio signals are
for the pilot on the nosewheel steering control, and an
routed.
interphone/transmit switch (on the copilot’s side panel)
labelled INPH/XMIT is provided for the copilot. The Operation
observer’s station has an audio control panel and jack
box (Figure 1) on which is mounted a transmit/interphone Multiplexing
(XMIT/INPH) toggle switch, microphone jack, headset Multiplexing is the process of combining several
jack, and ON/OFF (OBSERVER’S LT) toggle switch. measurements for transmission on the same signal
The audio system also contains a ground crew jack, path. In this system, each audio control panel contains
located on the forward fuselage (left hand side) and a multiplexing transmitter, and for each there is a control
an additional ground crew jack, located on the refuel/ card in the remote electronics unit (REU) containing a
defuel panel in the right engine nacelle. Common to all corresponding multiplex receiver. The transmitter scans,
stations and jacks is the primary interface component in fixed sequence, each volume control and switch on the

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 deHavilland Dash 8 100/300 23 - Communications

Figure 18 – Audio Integrating

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 deHavilland Dash 8 100/300 23 - Communications
audio control panel 20 times per second. Each volume XMIT, or using the copilot’s hand microphone. Operation
level scanned is transmitted as an analog voltage level, of the copilot’s hand microphone overrides both the
corresponding to the volume control position; and each copilot’s boom and mask microphones. Pressing the PTT
switch position is scanned for a high or low voltage level. switch also produces a mic control signal which keys the
This analog data is sent out on the data line to the REU. selected transmitter. During transmission, sidetone from
In the REU, the appropriate signal is switched on, and the transmitter is applied to the audio integrating system.
its volume level set as demanded by the position of each In addition, both the pilot’s and copilot’s microphone
volume control and switch on the audio control panel. audio is constantly applied to the cockpit voice recorder,
regardless of the position of either the pilot’s or copilot’s
Modes of Operation
PTT/INPH selection.
The audio integrating system provides communications
Communications Radio Reception
radio transmission, communications radio reception,
navigation radio reception, flight deck interphone, and For communications radio reception, the desired radio
normal or emergency operation. receiver audio output is selected by pressing in the
appropriate push−on/push−off/turn volume control VHF
Communications Radio Transmission
1, VHF 2 or (when installed) HF, UHF or FM. Pressing in
For communications radio transmission, the desired radio the control switches the volume control into the circuit;
transmitter is selected by rotating the MIC (microphone) pressing the control again disconnects the volume
selector switch on the audio control panel to VHF 1, control, and rotating the control adjusts audio volume.
VHF 2 or (when installed) HF, UHF or FM. Microphone Communications receiver audio output from the REU
selection is made by setting the MIC toggle switch to is applied to the cockpit voice recorder, appropriate
either MASK or BOOM (usually BOOM). With the desired headphones and cockpit speaker (when selected on).
radio frequency selected at the appropriate audio control Cockpit speaker audio is selected by pressing in the
panel, transmission by the pilot is possible by holding push−on/push−off/turn volume control labelled SPKR/
the PTT/INPH switch (control column handwheel) at VOL (speaker/volume).
PTT, or pressing and holding the PTT switch (nosewheel
NOTE: Speaker audio is muted when the respective
steering arm), or by using the pilot’s hand microphone.
PTT/INPH switch on the pilot’s or copilot’s
Operation of the pilot’s hand microphone overrides both
control wheel is selected to PTT or INPH,
the pilot’s boom and mask microphones. Transmission by
or when the PTT switch on the nosewheel
the copilot is possible by holding the copilot’s PTT/INPH
steering arm is pressed.
switch (control column handwheel) at PTT, or setting and
holding the INPH/XMIT switch (copilot’s side panel) to

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Figure 19 – Audio Control Panel

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 deHavilland Dash 8 100/300 23 - Communications
Navigation Radio Reception station headset/microphone is plugged into the jack at
the forward ground crew station, and indicates AFT when
For navigation radio reception, the desired navigation
a ground crew headset/microphone is plugged into the
radio receiver audio output is selected by pressing in
jack labelled GROUND CREW JACK on the refuel/defuel
the appropriate push−on/pushoff/turn volume control
panel. The FWD and AFT advisory lights alert the flight
(VOR−MLS 1, VOR−MLS 2, DME 1, DME 2, ADF 1,
crew that interphone communication with a ground crew
ADF 2 or MKR). Pressing in the control switches the
station may be made, and also indicates the station.
volume control into the circuits; pressing the control
If either the pilot’s or copilot’s audio system fails, the
again disconnects the volume control, and rotating the
affected crew member can monitor the audio integrating
control adjusts audio volume. Navigation radio receiver
system by plugging his headset into the HEADPHONES
audio output from the REU is applied to the cockpit voice
− AUX (auxiliary) jack on his jack panel.
recorder, appropriate headphones, and cockpit speaker.
Emergency Operation
Interphone
Emergency operation is selected either automatically
The interphone system is a five−way party line,
or manually. Emergency operation is automatically
comprising the pilot, copilot, observer, ground crew
selected if a power failure occurs within or to the Remote
forward jack (L.H. nose) and ground crew jack on the
Electronics Unit. Manual selection is made by setting the
refuel/defuel panel (R.H. nacelle). Only the pilot, copilot
NORM/EMER (normal/emergency) switch to EMER. In
and observer have the capability of controlling the
emergency operation, the pilot’s headphone is connected
audio volume and microphone selection. Interphone
directly to VHF 1 and VOR 1 − MLS 1 receiver, and the
communication from any of these three stations requires
pilot’s microphone is connected directly to the VHF 1
that the operator select INT (interphone) on the rotary
microphone input, so that both audio signals bypass all
MIC (microphone) selector switch and press XMIT, PTT,
amplifiers or other active circuitry normally in the audio
hand mic switch or INPH switch. If INT is not selected on
path. Similarly, the copilot’s and observer’s headphones
the rotary MIC selector switch, then interphone is only
are connected directly to VHF 2 and VOR 2 − MLS 2
possible by pressing INPH. Either action permits all flight
receivers, and the microphones connected directly to
crew stations to receive interphone audio by pressing
the VHF 2 transmitter. The pilot’s and copilot’s hand
the SERV/INT (service/interphone) selector switch. The
microphones are not operational during emergency
ground crew forward station and the ground crew station
operation. Either the boom or mask microphone must be
on the refuel/defuel panel receive interphone audio at
used for emergency operation, and the unused (boom or
all times. A ground crew (GND CREW) advisory light
mask) microphone disconnected. The interphone system
(at the left side of the nosewheel steering arm) comes
is not operational during emergency operation.
on and indicates FWD (forward) when a ground crew

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 deHavilland Dash 8 100/300 23 - Communications

Figure 20 – Interphone/Emergency - ACP

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 deHavilland Dash 8 100/300 23 - Communications
STATIC DISCHARGING (T.C.O. MFG. Operation
CORP.) As the aircraft moves through the air, the aerodynamic
end cap at the trailing end of each discharger creates
Description an area of low pressure around the slightly protruding
The static discharging system consists of dischargers wire tips. This reduction in pressure increases discharge
which dissipate electrostatic charges from the aircraft efficiency and allows ionization to take place in the
structure to the surrounding air, to minimize radio slipstream, due to the impressed potential between the
interference caused by these charges. electrified aircraft and the surrounding air dielectric.

Components
Two types of static dischargers are used: DD−2 (trailing
edge discharger) and TID−1 airfoil tip discharger. Type
DD−2 is approximately 6−3/8 inches in length, and
type TID−1 is approximately 4 inches in length. On Pre
Mod 8/0887 aircraft, twenty type DD−2 dischargers are
installed: four on each aileron trailing edge, two on each
elevator trailing edge, one on each elevator tip trailing
edge and six on the rudder trailing edge. On aircraft
with Mod 8/0887, nineteen type DE−2 dischargers are
installed: four on the left aileron trailing edge, three
on the right aileron trailing edge, two on each elevator
trailing edge, one on each elevator tip trailing edge,
and six on the rudder trailing edge. Four type TID−1
dischargers are installed: one on each wing tip and one
on each elevator tip. Each static discharger consists of
a semi−flexible resistive element covered with shrink
tubing, a wire bundle protruding from the trailing end and
a threaded portion at the leading end for mounting. Each
discharger is mounted by screwing the threaded end of
the discharger into a tapered sleeve adapter which in turn
is secured to the discharger base by means of a screw.

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Figure 21 – Static Discharging - T.C.O

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 deHavilland Dash 8 100/300 23 - Communications
STATIC DISCHARGING (CHELTON of the discharger rod and tip assembly, leaving
approximately 1/8 inch (.32 cm.) carbon tip
MINIPROBE) material exposed.
Description Operation
The static discharging system consists of dischargers
As the aircraft moves through the air, the aerodynamic
which dissipate electrostatic charges from the aircraft
end cap at the trailing end of each discharger creates
structure to the surrounding air, to minimize radio
an area of low pressure around the slightly−protruding
interference caused by these charges.
carbon tip. This reduction in pressure increases
Component Details discharge efficiency, and allows ionization to occur in the
slipstream, due to the impressed potential between the
■■Two types of static dischargers are used: type
electrified aircraft and the surrounding air dielectric.
2−11SC−1 and type 2−18SC−1. Type 2−11SC−1
is approximately 8 inches in length, with a straight
taper sleeve fitting. The type 2−18SC−1 is
approximately 6 inches in length with an angled
tapered sleeve fitting.
■■Nineteen type 2−11SC−1 dischargers are
installed: four on the left aileron trailing edge, three
on the right aileron trailing edge, three on each
elevator trailing edge, and six on the rudder trailing
edge.
■■Four type 2−18SC−1 dischargers are installed:
one on each wing tip, and one on each elevator
tip.
■■Each static discharger consists of a resistive
coated fibre glass rod with a pellet of composite
carbon−based material at the tip. The pellet
is fitted into an aluminum alloy sleeve, which
in turn is fitted onto the discharger rod by
means of conductive epoxy cement. A resistant
sheathing is heat−shrunk over the entire length

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 deHavilland Dash 8 100/300 23 - Communications

Figure 22 – Static Discharging (Chelton)

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 deHavilland Dash 8 100/300 23 - Communications
COCKPIT VOICE RECORDER SYSTEM chance for survival of the unit in event of a crash. The
control unit contains a built-in microphone and pre--
(FAIRCHILD FA2100CVR) amplifier, HEADSET monitor jack, TEST pushbutton
Description switch, test monitor meter, and an ERASE pushbutton
switch. The front panel of the recorder unit contains a
The cockpit voice recorder (CVR) system provides phone MONITOR jack, a carrying handle, and the ULD.
continuous four-channel recordings of all flight crew The TEST switch, HEADSET jack and meter are used to
communications and conversations during the time test the cockpit voice recorder system.
the aircraft electrical system is powered. The system
recordings provide an aid in an investigation, should the Power Supplies and Grounds
aircraft be involved in an accident. The ac and dc power supplies and grounds for the
The system consists of a COCKPIT VOICE RECORDER system are shown in the block diagram. The 115 volt
(CVR) control unit, a cockpit voice recorder, and 400.Hz primary power supply is routed to the recorder
underwater locating device (ULD). The CVR control unit through energized contacts of a relay (K4) in the auto
picks up flight crew conversations which are applied to flight control system (AFCS) interface unit. The relay,
the recorder as amplified electrical signals. In addition, along with erase interlock relay K7, is powered from
the control unit provides facilities for monitoring recording the 28 volts dc Left essential bus on the left dc circuit
quality and for checking system operation; the unit also breaker panel, through the CVR circuit breaker located
contains a switch for erasing the recordings. The recorder at M2. The ground connection to the relay is routed
is a solid state unit that records data in a solid state through an acceleration switch. In event of a crash, the
memory capable of continuous 30-minute recording, and acceleration switch disconnects the ground to deenergize
is housed in an armored enclosure to ensure survival in the relay, which in turn disconnects the primary power to
event of a crash. The recorder automatically erases as the recorder, and shuts off the system. The ULD is not
it records, so that only the last halfhour of recording is electrically connected to the aircraft, or to the CVR unit.
retained. Power is provided by a self-contained battery with a life
expectancy of approximately two years.
Components
Operation
The main components of the system consist of the
COCKPIT VOICE RECORDER control unit and the System inputs and Recording
recorder unit. The control unit is located in the flight
The four channel inputs to the CVR system consists of
compartment. The recorder, with the ULD attached, is
channel 1, public address audio; channel 2, copilot’s
located in the tail cone; this position offers maximum
audio; channel 3, pilot’s audio; channel 4, control unit

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 deHavilland Dash 8 100/300 23 - Communications

Figure 23 – SSCVR and Component Locations

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 deHavilland Dash 8 100/300 23 - Communications
microphone audio. Each channel input is recorded in the PSEU. When the park brakes are applied, switch
digital memory. 3151-S1 in the center console closes to connect a
ground through the closed loop circuit in the PSEU to
System Monitoring
energize relay K7 in the AFCS interface unit. Power to
The quality of the recording may be checked at arty time relay K7 is provided from the same source as relay K4.
the system is operating by means of a 600 ohm headset The energized contacts of relay K7 complete the erase
plugged into the HEADSET jack on the control unit, or interlock signal from the control unit to the recorder With
plugging a PEI into the connector on the recorder unit. this circuit completed, the recording maybe completely
The audio output and the monitor meter indication on the erased in about five to ten seconds, by a bulk erase
control unit provide monitoring of all four channels at the sequence initiated from the ERASE pushbutton on the
same time. control unit. As a prevention against accidental erasure,
the pushbutton must be activated for at least two seconds
Test
to initiate the erasing process. During the erase period, a
The operation of all four audio channels may be checked 400 Hz tone will be heard in the headset.
by pressing the TEST pushbutton on the control unit
Underwater Locating Device
panel while a 600-ohm headset is plugged into the
HEADSET jack on the control unit, or plugging a PI into The underwater locating device (ULD) is mounted
the connector on the recorder unit. When the TEST on a bracket fastened to the front cover of the voice
pushbutton is pressed, a 600 Hz tone is applied to each recorder(CVR). The ULD is held in the bracket by a cover
of the four record channels alternately for approximately plate which is secured by four flat-head screws and
0.8 seconds. Each channel records the 600 Hz tone lockwashers. The ULD transmits ultrasonic pulses when
along with any audio inputs. The recording is detected immersed in water, to assist in locating a submerged
by the monitoring system to provide audio and a 600 Hz CVR. The unit consists of a small cylindrical transmitter-
tone at the headset, and the monitor meter indicates 8 pinger, powered by a self-contained mercury battery; it
(minimum). is activated automatically upon immersion in water. It
transmits on a frequency of 37 KHz for distances of up to
Recording Erase
one mile in all directions.
Recordings may be erased completely only when the
aircraft is on the ground and the park brakes are applied.
When the aircraft is on the ground, the proximity switch
sensor system in the landing gear operates to close
the loop circuit when logic equation E050 is satisfied in

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 deHavilland Dash 8 100/300 23 - Communications

Figure 24 – SSCVR Block Diagram (1 of 2)

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 deHavilland Dash 8 100/300 23 - Communications
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 deHavilland Dash 8 100/300 23 - Communications

Figure 25 – SSCVR Block Diagram (2 of 2)

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 deHavilland Dash 8 100/300 23 - Communications
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 DHC 8 -300
(Differences)
Chapter

23
COMMUNICATIONS
© Jazz Air LP, 2008. All rights reserved. No part of these materials may be reproduced, stored in any material form
(including photocopying or storing on any medium by electronic means) without the prior written permission of the
copyright holder, except in accordance with the provisions of the Copyright Act. The doing of any unauthorized act in
relation to a copyright work may result in a civil claim for damages and/or criminal prosecution.
 deHavilland Dash 8 100/300 23 - Communications
DHC-300 Differences −− A combined push on/push off switch−volume
control, labeled SERV/INT, for interphone
communication with ground crew members. The
Audio Integrating System switch contains a light which comes on when the
switch is selected ’on’.
Audio Control panel
−− A BOOM − MASK selector switch, to enable
The audio control panel contains: use of either boom microphone or oxygen mask
−− Five combined push on/push off switch−volume microphone.
controls for selection of the following −− A HOT MIC selector switch. In the ON position
communications system receiver−transmitters: the boom, mask, and hand microphones are
VHF1, VHF2, HF, UHF, and FM (Note that not automatically and continuously keyed (’hot’) for
all of these systems may be installed in a given interphone mode only.
aircraft). Each switch contains a light which comes
on when the switch is selected ’on’.
−− Seven combined push on/push off switch−volume
controls for selection of the following navigation
system receivers: VOR 1, VOR 2, DME 1, DME 2,
ADF 1, ADF 2, and MKR (marker beacon) (Note
that not all of these systems may be installed in a
given aircraft). Each switch contains a light which
comes on when the switch is selected ’on’.
−− Microphone/interphone rotary selector switch
with the following positions: VHF1, VHF2, HF,
UHF, FM, INT (interphone), and PA (passenger
address).
−− A combined push on/push off switch−volume
control, labeled SPKR VOL, for the associated
flight compartment speaker, pilot and copilot’s
only. The switch contains a light which comes on
when the switch is selected ’on’.

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 deHavilland Dash 8 100/300 23 - Communications

Figure 26 – ACP Series 300.

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