Northern Airborne Technology AA83-001 User Manual rev.4.10

SM09-2

AA83-001 InterMUSIC™
Stereo Intercom System

INSTALLATION AND OPERATION MANUAL

REV 4.10 October 20, 2004

Northern Airborne Technology Ltd.

1925 Kirschner Road

Kelowna, BC, Canada.

V1Y 4N7

Telephone [phone]

Facsimile [phone]

Copyright 2004 by Northern Airborne Technology

CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.

SM09-2 Rev. 4.10 AA83-001 InterMUSIC™ Stereo Intercom System Manual

Periodically NAT will release manual amendments. In order to maintain the most
accurate and up to date manual these amendments should be carried out immediately
upon receipt and recorded on the following amendment record.

AMENDMENT RECORD

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Insert any Amendment Instruction sheets after this page.

Oct 20, 2004 Page ii

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SM09-2 Rev. 4.10 AA83-001 InterMUSIC™ Stereo Intercom System Manual

Table of Contents

Section Title Page

1 Description

1.1 Introduction 1-1

1.2 Purpose of Equipment 1-1

1.3 Features 1-1

1.3.1 Stereo & Intercom Special Features 1-1

1.3.2 Communication Functions 1-1

1.4 Specifications 1-2

1.4.1 Electrical Specifications 1-2

1.4.2 Physical Specifications 1-3

1.4.3 Environmental Specifications 1-3

2 Installation

2.1 Introduction 2-1

2.2 Unpacking and Inspection 2-1

2.2.1 Warranty 2-1

2.3 Installation Procedures 2-1

2.3.1 Warnings 2-1

2.3.2 Cautions 2-2

2.3.3 Cabling and Wiring 2-2

2.3.4 Installation Notes 2-2

2.3.5 Adjustments 2-3

2.3.6 Setting Music Input Compatibility 2-4

2.3.7 Mechanical Installation 2-4

2.3.8 Post-Installation Checks 2-5

2.3.9 Final Check 2-6

2.4 Continued Airworthiness 2-7

2.5 Accessories Required 2-7

2.6 Installation Drawings 2-7

3 Operation

3.1 Introduction 3-1

3.2 General 3-1

3.2.1 Stereo & Intercom Special Features 3-1

3.2.2 Communication Functions 3-1

3.3 Controls and Indicators 3-2

3.3.1 ICS VOL/VOX 3-2

3.3.2 MUSIC VOL/COPILOT VOX 3-2

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SM09-2 Rev. 4.10 AA83-001 InterMUSIC™ Stereo Intercom System Manual

Section Title Page

3.3.3 Annunciator 3-2

3.3.4 VOX Operation 3-3

3.3.5 Mode Switch 3-3

3.3.6 Automatic Fail-safe 3-4

3.3.7 Muting Explanation 3-5

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SM09-2 Rev. 4.10 AA83-001 InterMUSIC™Stereo Intercom System Manual

Section 1 Description

1.1 Introduction

This manual contains information on the AA83-001 InterMUSIC™. All derivative products
will be covered by manual supplements, which can be obtained from NAT as required.

Information in this section consists of purpose of equipment, features and specifications.

1.2 Purpose of Equipment

The AA83-001 is a 4-place stereo voice-activated intercom that provides full intercom
capabilities for the pilot and copilot and two passengers (PAX). It provides
entertainment and communication audio in full stereo to all four headsets, and

transceiver control for both the pilot and co-pilot. The InterMUSIC
intercoms allows several installation configurations - from single unit systems, to fully
independent stations for the pilot, copilot and passengers. For expanded systems, tie
line connections are compatible with other NAT systems including AA80, AA82, AMS4x
and AA9x series units.

™

family of stereo

1.3 Features

1.3.1 Stereo & Intercom Special Features

The stereo music audio is muted during transmit or intercom operation and when radio
receive audio is detected, permitting greater intelligibility of incoming transmissions.
The AA83-100 muting depth adjustment ranges from complete music muting to gentle
background music on command, with a fast attack and slow level return for optimum
user comfort. Each microphone is individually gated, for the best possible noise
performance during VOX operation. A front panel annunciator allows easy visual
setting of the VOX threshold, and also indicates transmit operation.

1.3.2 Communication Functions

The AA83-001 provides full boom-mic transmit and ICS functions for the pilot and co-pilot,
and provides ICS and radio monitor operation for two additional passengers. Pilot priority
on transmit and pilot isolation (direct connection to the aircraft radio system) are standard
features on all NAT intercom systems. The AA83-001 can support PTT ICS operation for
all users, and can be wired to cyclic/yoke switches for both TX and ICS functions.

The balance adjustment pots permit signals to be shifted in the user's acoustic listening
space so that tower transmissions appear to come from one area, and intercom from
another. This greatly aids in signal recognition and more accurately reproduces a
natural listening environment for the flight crew.

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1.4 Specifications

1.4.1 Electrical Specifications

Input Power: +11 to +32 Vdc. Nominal 14/28 Vdc systems

Supply Current: 0.4 A max. (full output power, all users)

Headset Power: Typical 100 mW into each side each headset
(300 Ω ear element)

4 headsets total
Total maximum power 400 mW per channel

Indicators: Transmit (Green LED)
ICS (Amber LED)

Inputs: 4 microphones 'carbon equivalent'
250 mVrms for full output
150 Ω input impedance

2 TX keylines Active ground, for Pilot & Copilot

4 ICS keylines Active ground, for all users

2 music inputs Compatible, left & right
Configurable for either Walkman™/Discman™

phones compatible (3 Vp-p), or Line Output
compatible (100-500 mV @ 10 kΩ)

1 Aircraft radio input

2.5 Vrms for full output
1 kΩ input impedance

1 bi-directional ICS Tie Line
1 Vp-p for full output

2.2 kΩ input impedance

Outputs: 4 aircraft stereo headsets (300 Ω/side)

Not designed for 8 Ω headsets

1 radio microphone output to aircraft audio

panel

1 TX keyline output (hard ground for TX).

Logic: TX, active ICS, and incoming Receive Audio all

mute the music channel (Muting depth
adjustable)

Fast attack, slow return of music signal

Pilot TX priority

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SM09-2 Rev. 4.10 AA83-001 InterMUSIC™Stereo Intercom System Manual

1.4.2 Physical Specifications

Dimensions excluding front panel:

Height 1.30" (33.0 mm)

Length 5.60" (142.2 mm)

Width 2.60" (66.0 mm)

Weight 0.6 lbs (283.5 g) excluding external hardware

Mounting Horizontal or vertical through-panel mounting

1.4.3 Environmental Specifications

Temperature:
Operating -40° C to +70° C

Storage -55° C to + 85° C (survival)

Altitude 25,000 feet

Humidity 95% Non-condensing

Shock DO-160C category "P", panel mounting 6 G.

End of section 1

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SM09-2 Rev. 4.10 AA83-001 InterMUSIC™ Stereo Intercom System Manual

Section 2 Installation

2.1 Introduction

Information in this section consists of: unpacking and inspection procedures, installation
procedures, post-installation checks, and installation drawings.

2.2 Unpacking and Inspection

Unpack the equipment carefully and locate the warranty card. Inspect the unit visually
for damage due to shipping and report all such claims immediately to the carrier
involved. Note that each unit should have the following:

- AA83-001 InterMUSIC™

- Warranty Card

- Operator’s Manual

- Release certification

- Installation kit (Section 2.5)

Verify that all items are present before proceeding and report any shortage immediately
to your supplier.

2.2.1 Warranty

Complete the warranty card information and send it to NAT when the installation is
complete. If you fail to complete the warranty card, the warranty will be activated on
date of shipment from NAT.

Note: An appropriately rated facility, e.g. Certified Aircraft Repair Station, must install this

equipment in accordance with applicable regulations. NAT Ltd’s warranty is not
valid unless the equipment is installed by an authorized NAT Dealer. Failure to
follow any of the installation instructions, or installation by a non-certified individual
or agency will void the warranty, and may result in a non-airworthy installation.

2.3 Installation Procedures

2.3.1 Warnings

Do not bundle any lines from this unit with transmitter coax lines. Do not bundle any
logic, audio, or DC power lines from this unit with 400 Hz synchro wiring or AC power
lines. Do not position this unit next to any device with a strong alternating magnetic field
such as an inverter, motor or blower, or significant audio interference will result.

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2.3.2 Cautions

In all installations, use shielded cable exactly as shown and ground as indicated.
Significant problems may result from not following these guidelines.

All audio installations can be seriously degraded by incorrect wiring and shielding, and
may result in abnormal cross-talk, hum and ground-loop noise. Be especially careful
with all microphone wiring and Tie Line wiring, as these lines carry the lowest level
signals in the aircraft.

All microphone and headset jacks should be electrically isolated from the airframe or
significant ground loop noise may result.

2.3.3 Cabling and Wiring

All unshielded wire should be to MIL-W-22759 or equivalent. For shielded wire
applications, use Tefzel MIL-C-27500 shielded wire with solder sleeves (for shield
terminations) to make the most compact and easily terminated interconnect. Follow the
wiring diagrams in Section 2.6 as required.

Allow 3 inches from the end of the wire to the shield termination to allow the hood to be
easily installed. Note that the hood is a ‘clamshell’ hood, and is installed after the wiring
is complete. Aircraft harnessing should permit the unit to be lowered from the panel for
easy access to all side adjustments. Do NOT mount the unit until all adjustments have
been carried out.

All wiring should be at least 22 AWG, except power and ground lines, which should be
at least 20 AWG. Ensure that the ground connection is clean and well secured, and
that it shares no path with any electrically noisy aircraft accessories such as blowers,
turn and bank instruments or similar loads. Power to this unit must be supplied from a
separate breaker (1/2 A) or fuse (1/2 A fast), and not attached to any other existing
breaker without additional protection. The correct fuse is included with the AA83-001.

2.3.4 Installation Notes

All AA95/AMS4X Audio Controllers used with the AA83-001 must have the ICS Tie Line
and Gain Modifications installed. This will only be a concern on Audio Controllers with
S/N 1918 or before. If the AA83-001 is used with a second unit such as an AA82, you
may wish to install the 2.2 kΩ resistor shown in the installation drawing. This is used to
equalize ICS Tie Line loading when changing from the tie to split connections. If you
are not familiar with Tie Line techniques, request the installation bulletin from NAT
covering Tie Line theory and practice.

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2.3.5 Adjustments

The unit ships from the factory with all internal adjustments set to the normal test levels.
Once installed in the aircraft, it may be desirable to change some of these settings to
best suit the local operating environment.

CAUTION

Before performing the following adjustments ensure the aircraft radio’s
volume control is set to produce 2.5 Vrms ±10 % at the input to the
AA83-001, or the mute functions may not operate correctly.

The internal adjustments are located along the sides of the unit and are as follows:

2.3.4.1 ICS, RX, and MUSIC BAL.

These potentiometers are used to adjust the headset stereo balance.

Note: The balance adjustment pots permit signals to be shifted in the user's acoustic

listening space so that tower transmissions appear to come from one area, and
intercom from another. This greatly aids in signal recognition and more
accurately reproduces a natural listening environment for the flight crew.

2.3.4.2 ICS and MUSIC BASS

These potentiometers are used to adjust the amount of bass audio to the headsets.
Rotating ccw will lower the bass level, and cw will raise it.

2.3.4.3 RX VOL

To reduce the receive audio volume, rotate this potentiometer ccw, and to increase the
volume, rotate it cw.

2.3.4.4 MUSIC MUTE

The music mute level can be adjusted using this potentiometer.

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2.3.6 Setting Music Input Compatibility

The AA83-001 (S/N 1091and up) can be configured to be Low-Z or High-Z circuits by
two internal jumpers (J103 and J104), which can be accessed by removing the cover
and top PCB from the AA83-001. The AA83-001 is normally shipped from the

factory as a Low-Z version.

2.3.5.1 Jumper Adjustment

Refer to Component Locator AA83\001\924-0 in Section 6 of the AA83-001
Maintenance Manual. If any further information is required, contact the Product Support
department at NAT Ltd.

Note: The AA83-001 is a static sensitive device. Use proper ESD handling procedures

when the cover is removed.

The two types of music inputs are configured by the position of jumpers J103 and J104,
located on the main PCB near the access hole for Q101. Music input type is
determined as follows:

Low Z/Walkman™ compatible J103 and J104 Installed

High Z/Pre-Amp compatible J103 and J104 Removed

To gain access to the jumpers, remove the cover from the AA83-001. Remove the top
PCB by removing three panhead screws and carefully lifting it straight up.

When reassembling the unit ensure the pins and connector are aligned properly before
screwing the PCB down.

2.3.7 Mechanical Installation

The AA83-001 can be installed in a vertical or horizontal attitude directly on the
instrument console, using the AA83-IKC Installation kit (see Section 2.5 for details).

Before the unit is mounted, make all functional tests and trimpot adjustments. Be sure
the harness has enough clearance to permit the unit to be dropped down for re­adjustment, if needed later. Make sure unit is securely fastened to the panel, and that
the connector locks are tightened before any flight is attempted.

For proper installation, refer to the Drill Template (AA83\001\921-0) and the following
steps:

Note: The mounting nuts on the panel pots should not be removed at any time.

a) After deciding the attitude (vertical or horizontal) of the unit, drill the required

mounting holes in the aircraft panel and insert the AA83-001 from behind the panel.

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b) Remove the protective plastic film from the black metal faceplate, and position it

with the appropriate legend orientation facing out. Secure with the mounting
screws provided.

Note: Ensure that the aircraft panel is tightly ‘sandwiched’ between the

AA83-001 and the faceplate.

c) Rotate the inner and outer shafts of the ICS VOL / VOX potentiometer fully ccw.

The outer knob may be rotated by hand, but it may be necessary to temporarily
attach the inner ICS knob to facilitate this action. Align the white markers on the
knobs to the LIVE position on the faceplate label. Using a 0.05" Allen key,
tighten the knobs onto the potentiometer shafts.

d) Rotate the shaft of the MUSIC VOL potentiometer fully ccw. Align the white

marker on the knob to the MIN position on the faceplate label. Using a 0.05"
Allen key, tighten the knob onto the potentiometer shaft.

Note: Make sure there is enough clearance between the concentric knobs so

that rotating one does not also move the other. A piece of paper makes a
good spacer when setting up the clearance.

2.3.8 Post-Installation Checks

If any preset requires adjustment, be sure this is carried out before the aircraft leaves,
and that the unit and its mating connector are secured before departure. Make all
required log book entries, electrical load, weight and balance amendments and other
paperwork as required by your local regulatory agency.

2.3.7.1 Voltage/resistance checks

Do not attach the AA83-001 until the following conditions are met.

Check the following:

a) Check P101, pin <1> for +9 to +32 Vdc relative to ground.

b) Check P101, pin <16> for continuity to ground (less than 0.5 Ω).

c) Check P101, pins <11> and <12> for continuity to ground (less than 0.5 Ω) when

the relevant ICS switch is keyed.

d) Check all mic, phone, music, and key lines for shorts to ground or adjacent pins.

Check all key lines for correct operation.

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2.3.7.2 Power On checks

Install the AA83-001 and power up the aircraft’s systems, and turn on the radios and
accessories required. Verify normal operation of all functions. Refer to Section 3 for
specific operation details.

a) Begin with only the pilot's headset installed, no hand mic. Check for correct radio

operation (both receive and transmit) and ICS operation. Check yoke (or cyclic)
switch action.

b) If there is a music source in the system turn it on and verify that music is heard in

all modes except PLT ISO. Check for proper mute operation.

Note: Unusual buzzes, hums or other background audio may be symptomatic of

multiple grounds or noisy external systems sharing the same wire bundle.
Incorrect jack wiring is a common fault, especially for passenger stations, and
may cause loss of audio, a tone on the headset lines, or other problems.

c) Plug in the copilot's headset. Check for correct radio and ICS operation. Check

pilot's transmit priority. Check yoke or cyclic switch functions, if applicable.

d) Plug in the hand mic (if applicable to the installation), and test for correct

operation in all modes. It must activate the transmitter(s) in all cases.

e) Plug in any remaining headsets, and check for correct ICS operation.

f) To verify proper operation, all functions and levels should be checked in-flight.

Be sure headsets are of good quality and are installed correctly. Unless the AA83-001
has specifically been wired for mono operation NEVER USE MONO AIRCRAFT
HEADSETS in the system, as they will short out one side of the AA83-001 power
amplifier when installed in stereo jacks. This may result in eventual unit failure, which
IS NOT COVERED BY WARRANTY.

2.3.9 Final Check

Fly the aircraft and check levels and operation of all functions. You may wish to change
Bass or Balance controls after flight, depending on how the system performs with
regard to ambient noise.

Upon satisfactory completion of all performance checks, make the required log
entries and complete the necessary Regulatory Agency paperwork before
releasing the aircraft for service.

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2.4 Continued Airworthiness

Maintenance of the AA83-001 is ‘on condition’ only. Periodic maintenance of this
product is not required.

2.5 Accessories Required

Installation kit p/n AA83-IKC is required to complete the installation. The kit consists of
the following:

Quantity Description NAT Part #

1 D-min 44 Pin Female Crimp Installation Kit D44SL-IKC
1 AGC 1/2A Fuse 23-00-005
3 5/8” 6-32 Black Pan Head Screw 25-11-427
1 Fluted 1/8” ICS Knob 40-21-ICS3
1 Fluted 1/8” Music Knob 40-21-MUS3
1 Hole Overlay 43-10-083
1 Rectangular Faceplate 50-04-831

The NAT Part #: D44SL-IKC consists of:

Quantity Description NAT Part #

1 D-min 44 Socket Housing 20-20-044
44 Mini D Crimp Socket 20-26-703
1* Jack Screw Set 20-27-002
1* Lock Clip Set 20-27-004
1 25 pin Connector Hood 20-29-026

* Use as required.

2.6 Installation Drawings

DRAWING REV. DESCRIPTION TYPE

AA83\001\302-0 1.00 InterMUSIC System Block Diagram
AA83\001\403-0 1.20 InterMUSIC Stereo Intercom Interconnect
AA83\001\405-0 1.00 InterMUSIC Stereo Intercom Connector Map
AA83\001\921-0 1.00 Drill Template Mounting Plate

Section 2 ends after these Drawings

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Section 3 Operation

3.1 Introduction

Information in this section consists of the functional and operational procedures for the
AA83-001 InterMUSIC™ stereo intercom.

3.2 General

The AA83-001 InterMUSIC™ is a stereo intercom system that supports a pilot, copilot
and two passengers. It provides entertainment and communication audio in full stereo
to all four headsets, and transceiver control for both the pilot and copilot. The

InterMUSIC™ family of stereo intercoms allows several installation configurations from
single unit systems, to fully independent stations for the pilot, copilot and passengers.
Tie Line connections are compatible with other NAT systems including AA82, AMS40
and AA95 series units for expanded systems.

3.2.1 Stereo & Intercom Special Features

The stereo music audio is muted during transmit or intercom operation and when radio
receive audio is detected, permitting greater intelligibility of incoming transmissions.
The AA83-001 muting depth adjustment ranges from complete music muting to gentle
background music on command, with a fast attack and slow level return for optimum
user comfort. Each microphone is individually gated, for the best possible noise
performance during VOX operation. A front panel annunciator allows easy visual
setting of the VOX threshold, and also indicates transmit operation.

3.2.2 Communication Functions

The AA83-001 provides full boom-mic transmit and ICS functions for the pilot and co­pilot, and provides ICS and radio monitor operation for two additional passengers. Pilot
priority on transmit and pilot isolation (direct connection to the aircraft radio system) are
standard features on all NAT intercom systems. The AA83-001 can support PTT ICS
operation for all users, and can be wired to cyclic/yoke switches for both TX and ICS
functions.

The balance adjustment pots permit signals to be shifted in the user's acoustic listening
space so that tower transmissions appear to come from one area, and intercom from
another. This greatly aids in signal recognition and more accurately reproduces a
natural listening environment for the flight crew.

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3.3 Controls and Indicators

ICS VOL (Inner)

PILOT VOX (Outer)

MUSIC VOL (Inner)

COPILOT VOX

(Outer)

Mode Switch

Annunciator

3.3.1 ICS VOL/VOX

The ICS VOL/PILOT VOX control is a fluted concentric rubber knob on the left side of
the front panel.

The inner (front) knob is the ICS VOL control, which is used to set Intercom volume. It is
at minimum volume when fully counter-clockwise (ccw). As the knob is rotated
clockwise (cw), the ICS volume for crew and PAX increases. The ICS is muted during
transmit operations.

The outer (rear) knob is the PILOT VOX control. For full information on VOX operation,
see section 3.3.4.

3.3.2 MUSIC VOL/COPILOT VOX

The MUSIC VOL control is a fluted concentric rubber knob on the right side of the front
panel.

The inner (front) knob is the MUSIC VOL control, which is used to set normal music
volume. The volume is at minimum when fully counter-clockwise (ccw), and as the knob
is rotated clockwise (cw), the volume increases. Music is muted during transmit
operations.

The outer (rear) knob is the COPILOT VOX control. For full information on VOX
operation, see section 3.3.4.

3.3.3 Annunciator

The front panel annunciator is a bi-colour LED that shows intercom status.

If the LED is illuminated green, it indicates transmit activity, and if it is red, it indicates
VOX activity. For transmit with sidetone or mic activity, it will illuminate amber. The
green LED also indicates a possible stuck mic if still lit after transmission is concluded.

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3.3.4 VOX Operation

The VOX control is used to set the level of audio required to activate the microphones.
The AA83-001 provides three modes of intercom operation, selected by the position of
the VOX control.

LIVE ICS When the VOX control is positioned fully ccw, the relevant mics will be

live, and any sound picked up will be processed by the ICS system (hot
mic).

KEYED ICS When the VOX control is positioned fully cw to the MAX position, the

intercom will be in a keyed-only mode.

VOX ICS When the VOX control is positioned between fully cw and fully ccw, the

intercom is in VOX mode. To establish the VOX threshold, rotate the
control ccw until the LED turns red, and then rotate the control cw until the
LED goes dark. Continue turning the control cw until the desired voice
sensitivity is set.

3.3.5 Mode Switch

The Mode switch is a red three-position toggle switch that is used to select the
operational mode of the AA83-001.

3.3.5.1 Normal Mode

In normal use, the AA83-001 serves as a common intercommunication system for up to
four users, and a flow-through interface for connection to the ship's external
communication system. The front panel controls allow both the pilot and copilot (plus
the passengers) to set their respective VOX trigger points independently to match
different headsets or noise locations.

For normal operation, the MODE switch is set to the NORMAL (down) position. A
transmit command from either the pilot or copilot will send their microphone signal
through to the aircraft communication system. Correct operation will be indicated by the
front panel indicator lighting green.

3.3.5.2 Pilot Isolation Operation

In normal operation, the pilot, copilot, and passengers hear the same signals from the
aircraft communication system. Sometimes this is not desirable from the pilot's
perspective, such as when he needs to communicate with the tower on approach or has
a heavy traffic load, and is not interested in the discussions on the intercom.

The MODE switch has a middle position, marked PILOT ISO, which disconnects the
pilot from the internal amplifier of the AA83-001 and connects the pilot directly to the
aircraft communication system. All other users are unaffected and continue to use the
entertainment and intercom functions of the AA83-001.

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The pilot has no ICS or music operation when selected to PIL ISO, and all his signals
are presented in mono format during this mode.

This mode is 'fail-passive', meaning that it requires no power to operate and is the same
mode the box goes into automatically when power is lost to the AA83-001. In this
way, switch over is immediate for the pilot and there is no possibility of lost
communication because of a lack of pilot action. Note that the pilot's boom mic is sent
directly to the radio in this mode, and only a PTT key input is needed to transmit.

3.3.5.3 Tie/Split Operation

The MODE switch has one further position, which can be used in expanded systems for
more complex audio circuits. If an outboard AA82 has been installed (or some other
NAT system with tie line capability), then this switch will open and close the tie line
output to create common or split intercom circuits with the external system.

In all positions other than SPLIT, the ICS tie line is sent to outside systems for common
intercom operation. This can be used for common communication from front to rear (for
example) in a larger aircraft. When set to the SPLIT position, the AA83-001 cuts the tie
line, breaking the two units into individual intercom circuits with isolated conversations.
In this way, many different circuit combinations can be set up, depending on what
device is hooked to the tie line.

With no external unit, the SPLIT position has no function within the AA83-001.

3.3.6 Automatic Fail-safe

In the event of a power failure, automatic fail-safe operation will be activated. This
routes the pilot’s phones, mic audio, and mic PTT directly to the COM radio. Copilot and
passengers will have no ICS, music, or receive functions.

The pilot mic is directly connected to the transceiver mic. Mic bias is provided by the
transceiver, not the AA83-001. The pilot TX keyline is directly connected to the
transceiver.

During receive mode, receive audio is directly connected from the audio source to the
pilot phones, and during transmit mode, the sidetone audio is directly connected from
the audio source to the pilot phones. In both cases, copilot and passengers have no
ICS, music, sidetone, or receive functions.

In the unlikely event of an AA83-001 circuit failure that results in a communication
problem, the automatic fail-safe mode can be enabled by pulling the AA83-001 circuit
breaker.

Note: In Automatic Fail-Safe mode, the receive/sidetone levels may require adjustment

at the audio source.

The pilot should confirm that all aspects of Automatic Fail-Safe operation are
working before accepting the aircraft into service.

Page 3-4 Oct 20, 2004

ENG-FORM: 806-0106.DOT

CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.

SM09-2 Rev. 4.10 AA83-001 InterMUSIC™ Stereo Intercom System Manual

3.3.7 Muting Explanation

When transmitting, any music will be muted quickly, and will slowly return when
transmission is completed. Music will also be muted when ICS or RX functions are
active. The degree of muting is set via the MUSIC MUTE adjustment explained in the
installation section of this manual. The relative volume of the music can be changed
from the front panel by the knob marked with a musical note.

Below is a simple chart to aid in understanding audio switching in the NORMAL
Operation mode. The following terms are used:

' Active' - Function being used.
' Muted' - Functions that are overridden by the active condition.
' Idle' - Functions that are not active, but still available for use.

Music ICS RX Pilot TX Copilot TX

Active Idle Idle Idle Idle
Muted Active Idle Idle Idle
Muted Idle Active Idle Idle
Muted Muted Idle Active Muted
Muted Muted Idle Idle Active

End of section 3

Oct 20, 2004 Page 3-5

ENG-FORM: 806-0106.DOT

CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.