PS Engineering PAC24 User manual

9800 Martel Road
Lenoir City, TN 37772
www.ps-engineering.com
PAC24
Audio Control Panel and Intercom System
Installation
and
Operation Manual
FAA-Approved TSO C50c
JAA-Approved JTSO C50c
Document P/N 200-240-0010
Revision 29, September 2021
PS Engineering, Inc. 2021 ©
Copyright Notice
Any reproduction or retransmittal of this publication, or any portion thereof, without the expressed written permission of PS
Engineering, Inc. is strictly prohibited. For further information contact the Publications Manager at PS Engineering, Inc., 9800
Martel Road, Lenoir City, TN 37772. Phone [phone], email [e-mail].
In certified aircraft, warranty is not valid unless this product is installed by an
Authorized PS Engineering dealer.

Table of Contents
SECTION I GENERAL INFORMATION .........................................................................................................1-1
Contents
SECTION I GENERAL INFORMATION.........................................................................1-1
1.1 INTRODUCTION.............................................................................................................1-1
1.2 SCOPE................................................................................................................................1-1
1.3 EQUIPMENT DESCRIPTION........................................................................................1-1
1.4 APPROVAL BASIS - ........................................................................................................1-2
1.5 SPECIFICATIONS...........................................................................................................1-2
1.6 EQUIPMENT SUPPLIED................................................................................................1-3
1.7 EQUIPMENT REQUIRED BUT NOT SUPPLIED.......................................................1-4
1.8 LICENSE REQUIREMENTS..........................................................................................1-4
SECTION II - INSTALLATION.........................................................................................2-1
2.1 GENERAL INFORMATION...........................................................................................2-1
2.1.1 SCOPE..............................................................................................................................2-1
2.1.2 UNPACKING AND PRELIMINARY INSPECTION...................................................................2-1
2.2 SYSTEM CONFIGURATION .................................................................................................2-1
2.2.1 DISASSEMBLY AND ACCESS..............................................................................................2-1
2.2.2 SINGLE/DUAL CONFIGURATION JUMPERS J4 &J5............................................................ 2-3
2.2.3 DIP SWITCH CONFIGURATIONS........................................................................................ 2-4
2.2.4 PASSENGER AND EXPANSION DIP SWITCH CONFIGURATIONS ........................................2-4
2.2.5 DIP SWITCH CROSS REFERENCE.......................................................................................2-6
2.3 EQUIPMENT INSTALLATION PROCEDURES.......................................................................2-8
2.3.1 MOUNTING REQUIREMENTS.............................................................................................2-8
2.3.2 COOLING REQUIREMENTS ................................................................................................2-9
2.3.3 MOUNTING RACK INSTALLATION ....................................................................................2-9
2.3.4 TRAY AND CONNECTOR ASSEMBLY.................................................................................2-9
2.4 CABLE HARNESS WIRING..................................................................................................2-9
2.4.1 NOISE................................................................................................................................ 2-9
2.4.2 EXISTING KMA 24H INSTALLATION..............................................................................2-10
2.4.3 POWER ............................................................................................................................2-10
2.4.4 COMMUNICATIONS PUSH-TO-TALK (SINGLE PANEL INSTALLATION).............................2-10
2.4.5 AUDIO PANEL INTERFACE .............................................................................................. 2-10
2.4.6 TRANSMIT INTERLOCK ...................................................................................................2-10
2.4.7 "SWAP"MODE ................................................................................................................2-11
2.4.8 BACKLIGHTING............................................................................................................... 2-11
2.4.9 UNSWITCHED INPUTS......................................................................................................2-11
2.4.10 PA MUTE (J3, PIN 8).....................................................................................................2-11
2.4.11 PUBLIC ADDRESS (J3, PIN B)........................................................................................2-11
2.4.12 INTERCOM WIRING........................................................................................................2-11
2.4.13 ENTERTAINMENT INPUT (J3 PIN 7)............................................................................... 2-12
2.4.14 INTERCOM EXPANSION (P/N 11606 OR 11606R)..........................................................2-12
2.4.15 CVR OUTPUT................................................................................................................2-13
2.5 ADJUSTMENTS..................................................................................................................2-13
2.6 COMMUNICATIONS ANTENNA INSTALLATION NOTES...................................................2-13
2.7 TELECOMMUNICATIONS INTERFACE..............................................................................2-14
2.8 PAC24 PIN ASSIGNMENTS ...............................................................................................2-15

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page ii Rev. 29, Sept. 2021
2.9 POST INSTALLATION CHECKOUT....................................................................................2-16
2.10 UNIT INSTALLATION ......................................................................................................2-16
2.10.1 OPERATIONAL CHECKOUT............................................................................................2-16
2.11 FINAL INSPECTION.........................................................................................................2-17
SECTION III OPERATION................................................................................................3-1
3.1 SCOPE................................................................................................................................3-1
3.2 PAC24 CONTROLS ............................................................................................................3-1
3.3 POWER SWITCH (3) (EMG-FAIL SAFE OPERATION).......................................................3-1
3.3.1 SINGLE PANEL FAIL SAFE OPERATION.............................................................................3-1
3.3.2 DUAL PANEL FAIL SAFE OPERATION ...............................................................................3-1
3.4 COMMUNICATIONS SELECTION (2)...................................................................................3-2
3.4.1 TELEPHONE OPERATION (S5 SWITCH 4SELECTED ON)...................................................3-2
3.4.2 STUCK MICROPHONE PROTECTION ..................................................................................3-2
3.4.3 SWAP MODE (REMOTE TRANSFER OF COM TRANSCEIVERS) ............................................ 3-2
3.4.4 OBSERVER TRANSMIT SELECTION (PART NUMBER –0400 SERIES)...................................3-3
3.5 RECEIVE AUDIO SELECTOR (1).........................................................................................3-3
3.5.1 SPEAKER AMPLIFIER (4)...................................................................................................3-3
3.5.2 KEY “CLICK”....................................................................................................................3-3
3.6 SPLIT MODE .......................................................................................................................3-3
3.6.1 SPLIT MODE,SINGLE PANEL.............................................................................................3-3
3.6.2 SPLIT MODE,DUAL PANEL...............................................................................................3-4
3.6.3 SPLIT MODE,OBSERVER PANEL (-04XX)........................................................................3-4
3.7 INTERCOM OPERATION .....................................................................................................3-4
3.7.1 INTELLIVOX®VOX-SQUELCH..........................................................................................3-4
3.7.2 VOLUME CONTROL (3) .....................................................................................................3-5
3.7.3 INTERCOM MODES (5) ......................................................................................................3-5
3.7.4 ENTERTAINMENT INPUT ...................................................................................................3-6
3.8 TELEPHONE MODE.............................................................................................................3-6
SECTION IV- WARRANTY AND SERVICE...................................................................4-1
4.1 WARRANTY.........................................................................................................................4-1
4.2 FACTORY SERVICE.............................................................................................................4-1
APPENDIX A –INSTALLATION DRAWING ...................................................................A
APPENDIX B SINGLE UNIT INTERCONNECT WIRING (DOES NOT APPLY TO
050-240-0400, DUAL OBSERVER).............................................................................................A
APPENDIX C DUAL INTERCONNECT RADIO WIRING (ALL VERSIONS).............B
7.1 DUAL PAC24 CREW AUDIO WIRING,STANDARD (-0100, -0500, -0503) UNITS ................C
7.2 DUAL PAC24INTERCOM AUDIO WIRING WITH OBSERVER CONFIGURATION UNITS (050-
240-0400 ONLY)............................................................................................................................D
7.3 DUAL PAC24INTERCOM AUDIO WIRING WITH OBSERVER CONFIGURATION (050-240-
0400 ONLY)AND EXPANSION UNITS...............................................................................................E
APPENDIX D- INSTRUCTIONS FOR FAA FORM 337 AND CONTINUING
AIRWORTHINESS ......................................................................................................................A
8.1 INSTRUCTIONS FOR FAA FORM 337, AUDIO PANELS.........................................................A
8.2 INSTRUCTIONS FOR CONTINUING AIRWORTHINESS,AUDIO PANELS ...............................A
APPENDIX E –RTCA DO160D (EUROCAE ED-14) ENVIRONMENTAL
QUALIFICATION FORM...........................................................................................................A

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page iii Rev. 29, Sept. 2021
1.2 SCOPE...............................................................................................................................................................1-1
1.3 EQUIPMENT DESCRIPTION........................................................................................................................1-1
1.4APPROVAL BASIS -........................................................................................................................................1-2
1.5 SPECIFICATIONS...........................................................................................................................................1-2
1.6 EQUIPMENT SUPPLIED................................................................................................................................1-3
1.7 EQUIPMENT REQUIRED BUT NOT SUPPLIED .......................................................................................1-4
1.8 LICENSE REQUIREMENTS..........................................................................................................................1-4
SECTION II - INSTALLATION.........................................................................................................................2-1
2.1 GENERAL INFORMATION...........................................................................................................................2-1
2.1.1 SCOPE ............................................................................................................................................................2-1
2.1.2 UNPACKING AND PRELIMINARY INSPECTION .....................................................................................................2-1
2.2 SYSTEM CONFIGURATION...................................................................................................................................2-1
2.2.1 DISASSEMBLY AND ACCESS...............................................................................................................................2-1
2.2.2 SINGLE/DUAL CONFIGURATION JUMPERS J4 &J5 ..............................................................................................2-3
2.2.3 DIP SWITCH CONFIGURATIONS.........................................................................................................................2-4
2.2.4 PASSENGER AND EXPANSION DIP SWITCH CONFIGURATIONS............................................................................2-4
2.2.5 DIP SWITCH CROSS REFERENCE........................................................................................................................2-6
2.3 EQUIPMENT INSTALLATION PROCEDURES..........................................................................................................2-8
2.3.1 MOUNTING REQUIREMENTS..............................................................................................................................2-8
2.3.2 COOLING REQUIREMENTS .................................................................................................................................2-9
2.3.3 MOUNTING RACK INSTALLATION......................................................................................................................2-9
2.3.4 TRAY AND CONNECTOR ASSEMBLY ..................................................................................................................2-9
2.4 CABLE HARNESS WIRING ...................................................................................................................................2-9
2.4.1 NOISE...............................................................................................................................................................2-9
2.4.2 EXISTING KMA 24H INSTALLATION...............................................................................................................2-10
2.4.3 POWER ...........................................................................................................................................................2-10
2.4.4 COMMUNICATIONS PUSH-TO-TALK (SINGLE PANEL INSTALLATION).................................................................2-10
2.4.5 AUDIO PANEL INTERFACE ...............................................................................................................................2-10
2.4.6 TRANSMIT INTERLOCK....................................................................................................................................2-10
2.4.7 "SWAP"MODE................................................................................................................................................2-11
2.4.8 BACKLIGHTING...............................................................................................................................................2-11
2.4.9 UNSWITCHED INPUTS ......................................................................................................................................2-11
2.4.10 PA MUTE (J3, PIN 8)....................................................................................................................................2-11
2.4.11 PUBLIC ADDRESS (J3, PIN B)........................................................................................................................2-11
2.4.12 INTERCOM WIRING........................................................................................................................................2-11
2.4.13 ENTERTAINMENT INPUT (J3 PIN 7)................................................................................................................2-12
2.4.14 INTERCOM EXPANSION (P/N 11606 OR 11606R)...........................................................................................2-12
2.4.15 CVR OUTPUT...............................................................................................................................................2-13
2.5 ADJUSTMENTS...................................................................................................................................................2-13
2.6 COMMUNICATIONS ANTENNA INSTALLATION NOTES ......................................................................................2-13
2.7 TELECOMMUNICATIONS INTERFACE.................................................................................................................2-14
2.8 PAC24 PIN ASSIGNMENTS ................................................................................................................................2-15
2.9 POST INSTALLATION CHECKOUT......................................................................................................................2-16
2.10 UNIT INSTALLATION.......................................................................................................................................2-16
2.10.1 OPERATIONAL CHECKOUT............................................................................................................................2-16
2.11 FINAL INSPECTION .........................................................................................................................................2-17
SECTION III OPERATION................................................................................................................................3-1
3.1 SCOPE...............................................................................................................................................................3-1
3.2 PAC24 CONTROLS.............................................................................................................................................3-1
3.3 POWER SWITCH (3) (EMG-FAIL SAFE OPERATION)..........................................................................................3-1
3.3.1 SINGLE PANEL FAIL SAFE OPERATION ..............................................................................................................3-1
3.3.2 DUAL PANEL FAIL SAFE OPERATION.................................................................................................................3-1
3.4 COMMUNICATIONS SELECTION (2).....................................................................................................................3-2
3.4.1 TELEPHONE OPERATION (S5 SWITCH 4SELECTED ON)......................................................................................3-2
3.4.2 STUCK MICROPHONE PROTECTION....................................................................................................................3-2
3.4.3 SWAP MODE (REMOTE TRANSFER OF COM TRANSCEIVERS)................................................................................3-2
3.4.4 OBSERVER TRANSMIT SELECTION (PART NUMBER –0400 SERIES). ......................................................................3-3
3.5 RECEIVE AUDIO SELECTOR (1)...........................................................................................................................3-3

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page iv Rev. 29, Sept. 2021
3.5.1 SPEAKER AMPLIFIER (4) ...................................................................................................................................3-3
3.5.2 KEY “CLICK”....................................................................................................................................................3-3
3.6 SPLIT MODE........................................................................................................................................................3-3
3.6.1 SPLIT MODE,SINGLE PANEL .............................................................................................................................3-3
3.6.2 SPLIT MODE,DUAL PANEL ...............................................................................................................................3-4
3.6.3 SPLIT MODE,OBSERVER PANEL (-04XX) .........................................................................................................3-4
3.7 INTERCOM OPERATION.......................................................................................................................................3-4
3.7.1 INTELLIVOX®VOX-SQUELCH ..........................................................................................................................3-4
3.7.2 VOLUME CONTROL (3)......................................................................................................................................3-5
3.7.3 INTERCOM MODES (5).......................................................................................................................................3-5
3.7.4 ENTERTAINMENT INPUT ....................................................................................................................................3-6
3.8 TELEPHONE MODE .............................................................................................................................................3-6
SECTION IV- WARRANTY AND SERVICE ...................................................................................................4-1
4.1 WARRANTY.........................................................................................................................................................4-1
4.2 FACTORY SERVICE..............................................................................................................................................4-1
APPENDIX A –INSTALLATION DRAWING................................................................................................... A
APPENDIX B SINGLE UNIT INTERCONNECT WIRING (DOES NOT APPLY TO 050-240-0400)...........B
APPENDIX B DUAL INTERCONNECT RADIO WIRING (ALL UNITS) ......................................................B
7.1 DUAL PAC24 CREW AUDIO WIRING,STANDARD (-0100, -0500, -0503) UNITS....................................................B
7.2 DUAL PAC24INTERCOM AUDIO WIRING WITH OBSERVER CONFIGURATION UNITS (050-240-0400 ONLY).......B
7.3 DUAL PAC24INTERCOM AUDIO WIRING WITH OBSERVER CONFIGURATION (050-240-0400 ONLY)AND
EXPANSION UNITS..............................................................................................................................................................B
APPENDIX C- INSTRUCTIONS FOR FAA FORM 337 AND CONTINUING AIRWORTHINESS............ C
8.1 INSTRUCTIONS FOR FAA FORM 337,AUDIO PANELS........................................................................................... C
8.2 INSTRUCTIONS FOR CONTINUING AIRWORTHINESS,AUDIO PANELS ................................................................... C
APPENDIX D –RTCA DO160D (EUROCAE ED-14) ENVIRONMENTAL QUALIFICATION FORM..... D
Rev
Date
Change
9
March 2005
Clarified Expansion Grounding, also pin out diagram on 2-11
10
March 2006
Added cross reference tables for DIP switch settings 2.3.2
11
January 2007
Added Vertical Orientation Units
12
May 2007
Clarified DIP switches, Section 2.3
13
September 2007
Added Appendix F, P-T-T- Modifications
14
August 2008
Added information on DIP Access & Observer minimum
15
September 2008
Clarified PA Speaker configuration
16
October 2008
Corrected expansion unit part number
17
March 2009
Added information on hot mic mode disable, §3.7.4.2
18
April 2009
Corrected drawing notes
19
May 2008
Added Special Mission –0503 units
20
Oct 2009
Regenerated wiring diagrams for improved resolution
21
March 2010
Clarified Expansion wiring & DIP switch setting
22
February 2012
Redesigned Front Panel and implemented schematic changes
23
April 2013
Added notes on unswitched audio §2.4.9 & §2.4.14
24
December 2013
Corrected text for Crew mode in §3.7.3.2
25
February 2015
Changed number of connector pins supplied
26
May 2015
Improved graphic depictions for configurations
27
August 2018
Added Night Vision Goggle Compatible units
28
July 2020
Corrected table 2-4, in §2.2.4
29
September 2021
Revised Appendices for clarity, reformatted

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 1-1 Rev. 29, Sept. 2021
1 Section I GENERAL INFORMATION
1.1 INTRODUCTION
The PAC24 represents the finest in high-performance cockpit audio control and intercommunications. Us-
ing proprietary IntelliVox® design, this unit eliminates the requirements for intercom squelch adjustments.
The unit is designed for outstanding ergonomics and visually defined mode annunciation and selection.
The PAC24 was designed as either a single or a dual audio panel system.
In addition, a version is available that supports a 3rd transmit seat if desired (050-240-0400).
The PAC24 –0500 is available where a vertical orientation would be appropriate.
Before installing and/or using this product, please read this manual completely. This will ensure that you
will take full advantage of all the advanced features in the PAC24.
1.2 SCOPE
This manual provides detailed installation and operation instructions for the PS Engineering PAC24-series
of Audio Selector Panel/Intercom Systems. This includes the following units:
Model
Description
Part Number
PAC24
Standard (single or dual installation)
050-240-0100
PAC24
Observer 3rd Transmit Seat (Qty. 2 PAC24s)
050-240-0400
PAC24
Standard (same as -0100), with Vertical Orientation
050-240-0500
PAC24
Special Mission Application Units, Vertical
050-240-0503
PAC24
Standard PAC24, but with NVG Compatibility
050-240-8100
PAC24
Observer 3rd Transmit Seat (Qty. 2 PAC24s) with NVG
Compatibility
050-240-8400
PAC24
Standard/NVG (same as -8100), with Vertical Orientation
050-240-8500
Where the functions are identical to all units, it will be referred to herein as a PAC24. Otherwise, the appli-
cable units will be specified.
NOTE: Observer configuration (-0400) units cannot be mixed with Standard configuration units.
Observer units MUST be dual installations.
1.3 EQUIPMENT DESCRIPTION
The PAC24-series is a state of the art audio isolation amplifier and audio selector that contains an automat-
ic voice activated (VOX) intercom system. It can switch up to five transceivers (Com 1, Com 2 Com 3
Com 4 and Com 5) and 4 receivers (Nav 1, Nav 2, AUX (or ADF in –0500, -0503) and MKR).
•Five transceivers
•Full Duplex available (COM 5)
•Split mode in single audio panel installation
•Four switched receivers
•Two Unswitched inputs
•Speaker amplifier
•Separate Public Address output
•Push-button control with LED indication
•Intercom with Pilot Isolate and ALL mode (Crew mode with expansion unit)
•Monaural music input with SoftMute™

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 1-2 Rev. 29, Sept. 2021
The Duplex Telephone mode (COM 5) allows the PAC24 to act as an audio interface between aircraft
headphone and microphones and specific aircraft approved (FAA/FCC) cellular telephone equipment.
Warning : Use of non-aviation approved cellular telephone equipment may be prohibited by regulation.
PS Engineering is not responsible for unauthorized airborne use of cellular telephones.
For airborne use, the PAC24 must be interfaced with an approved system.
A fail-safe mode connects the pilot headphone and microphone to COM 1 if power is removed for any rea-
son, or if the power switch is placed in the Off (Fail-safe) position.
A voice activated (VOX) intercom is included in the PAC24. This system has PS Engineering’s exclusive
IntelliVox® circuitry that eliminates manual adjustments. The system contains five independent VOX mic
circuits, and only opens the specific microphone channel in use.
The intercom system incorporates pilot isolate (ISO) and ALL modes. A crew mode is ONLY available
with external expansion module P/N 11606.
A dual volume controls intercom level for the pilot, inner knob, and copilot/passengers (outer knob). Inter-
com squelch is automatic.
The PAC24 is form fit and function compatible with the King Radio KMA24H, part number 066-1055-71,
and may be compatible with 066-1055-70 depending on application.
1.4 APPROVAL BASIS -
FAA-TSO Approval.
The PAC24 Audio Selector Panels are FAA approved under TSO C50c (Audio Amplifiers). In addition, the
PAC24 is JAA-JTSO approved under LBA.N-O.10.510/003JTSO.
All systems comply with relevant portions of EUROCAE ED-14C/DO-160D (Environmental Conditions and Test Pro-
cedures for Airborne Equipment), ED12B/DO-178B (Software Considerations for Airborne Equipment) and ED-
18/DO-214 (Audio Systems Characteristics and Minimum Operational Performance Standards for Aircraft Audio Sys-
tems).
Operation is subject to the following conditions:
This device may not cause harmful interference.
This device must accept any interference received, including interference that may cause undesired opera-
tion.
1.5 SPECIFICATIONS
TSO COMPLIANCE
Audio Selector/Intercom:
C50c, Class A
APPLICABLE DOCUMENTS:
RTCA/DO-214
RTCA/DO-160D
RTCA/DO-178B
ENVIRONMENTAL Qualifications:
B1ZCABSRXXXXXXZBBBATMXXE2XXX
Temperature Range:
Operating:
Storage:
-20ºC to +55ºC with short term operating at +70°C
-55ºC to +85ºC
Altitude:
Up to 50,000 feet in a non-pressurized area of the
cockpit.
DIMENSIONS:
Height: 1.3 in. (3.3 cm) Width: 6.25 in. (16.9 cm)
Depth: 6.8 in. (17.3 cm) behind panel
WEIGHT (With Rack & Connectors):
1.5 lb. (0.54 kg)

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 1-3 Rev. 29, Sept. 2021
Specifications, Continued.
POWER REQUIREMENTS (Including Internal Lighting):
Voltage:
11 to 33 VDC
Maximum Current:
2.5 Amp (Externally protected by a 3 Amp circuit
breaker.)
Typical operating current:
Speaker off:
Speaker on, 28V, full radio volume
350 mA
1.5 A
Audio Selector Specifications
Audio selector panel input impedance:
510 
Input Isolation:
-60 dB (min.)
Speaker Muting:
-60 dB (min.)
Speaker Output (into 4 ) with no clipping
14 VDC:
28 VDC:
3 Watts (min.)
10 Watts (min.)
Receiver Inputs:
10
(Com 1, Com 2, Com 3, Com 4, Com 5, Nav 1,
Nav 2, ADF, DME, MKR)
Unswitched Inputs:
2
(examples: GPS WPT, Value, Autopilot Discon-
nect, Altimeter DH)
Transmitter Selections:
5
(Com 1, Com 2, Com 3 Com 4, Com 5)
Speaker Impedance:
4 –8 
Headphone Impedance:
150 –1000 
Headphone Output:
38 mW each headset, no clipping <1% THD
120 mW each headset with < 10% THD into
150
Microphone Impedance:
150 - 600 
Intercom Specifications
Intercom Positions:
Minimum of 5 places (with individual IntelliVox® cir-
cuits)
Music Input:
1 (Monaural)
Music Muting:
>-30 dB "Soft Mute" when Com or intercom active.
Distortion:
<1% THD @ 38 mW into 150
<10% THD @ 120mW into 150 
Mic Freq. Response, 3 dB:
300 Hz - 6000 Hz
Music Freq. Response, 3 dB:
100 Hz - 18kHz
1.6 EQUIPMENT SUPPLIED
1 ea. of the following units:
Model
Description
Part Number
PAC24
PAC24 Audio Control Panel with intercom
050-240-0100
PAC24 Observer
PAC24 Audio Control Panel for Observer installation (3rd Transmit seat)
050-240-0400
PAC24 Vertical
PAC24 Audio Control Panel with intercom, Vertical Orientation
050-240-0500
PAC24 Special
PAC24 Audio Controller, Special Mission Version, Vertical
050-240-0503
PAC24 /NVG
PAC24 Audio Control Panel with intercom
050-240-8100
PAC24 Observer /NVG
PAC24 Audio Control Panel for Observer installation (3rd Transmit seat)
050-240-8400
PAC24 Vertical /NVG
PAC24 Audio Control Panel with intercom, Vertical Orientation
050-240-8500
Observer (-0400 & -8400) units
must be dual installations, and
cannot be mixed with other part
numbers.

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 1-4 Rev. 29, Sept. 2021
PAC24 Installation Kit: 250-240-0001
Description
Quantity
Part
Number
PAC24 installation rack assembly
1
475-240-0040
Molex Connector Shell w/key, 50 pin, key 17/18
1
120-425-5002
Gold Plated Crimp Pins
42
425-001-0002
4 40 X 7/16 screw w/nylon patch
4
475-440-0007
Grounding bar
1
430-007-0001
6-32 X 3/4 pan head Phillips screw
2
475-632-0038
6-32 Nut Flat
2
475-632-0003
6-32 Lock Nut
2
475-632-0004
Cable Clamp
1
625-001-0002
#6-32 x ½” Flat head Phillips screw
6
475-632-0012
#6-32 Clip Nut
6
475-630-0002
Parts identification sheet
1
002-250-0240
1.7 EQUIPMENT REQUIRED BUT NOT SUPPLIED
a) Circuit Breaker: 1 ea. 3 amp
b) Cockpit Speaker, 4 recommended
c) Cabin or External Speaker 4 recommended
d) Headphone Jacks (as required)
e) Microphone Jacks (as required)
f) Headphones, 150 as required
g) Microphones, as required
h) Interconnect Wiring
1.8 LICENSE REQUIREMENTS
None

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 2-1 Rev. 29, Sept. 2021
NOTE
2 Section II - Installation
2.1 GENERAL INFORMATION
2.1.1 SCOPE
This section provides detailed installation and interconnect instructions for the PS Engineering PAC24-
Series Audio Control Panel/Intercom System.
Please read this manual carefully before beginning any installation to prevent damage and post-installation
problems. Installation of this equipment requires special tools and knowledge.
NOTE: The PAC24 requires specialized knowledge and tools for an effective installation. An appropriate-
ly rated Certified Aircraft Repair Station must install this equipment in accordance with applicable regula-
tions. PS Engineering, Incorporated warranty is not valid unless the equipment is installed by an authorized
PS Engineering, Incorporated 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 an unairworthy installation.
2.1.2 Unpacking and Preliminary Inspection
Use care when unpacking the equipment. Inspect the units and parts supplied for visible signs of shipping
damage. Examine the unit for loose or broken buttons, bent knobs, etc. Verify the correct quantity of com-
ponents supplied with the list in Section 1.6 (B). If any claim is to be made, save the shipping material and
contact the freight carrier. Do NOT return units damaged in shipping to PS Engineering. If the unit or ac-
cessories shows any sign of external shipping damage, contact PS Engineering to arrange for a replace-
ment. Under no circumstances attempt to install a damaged unit in an aircraft. Equipment returned to PS
Engineering for any other reason should be shipped in the original PS Engineering packaging, or other UPS
approved packaging.
2.2 System Configuration
The PAC24 can be easily configured for many different applications. This includes dual audio
panel installations.
The information below describes the various circuit jumper configurations and internal
switch selections. There are two sections, the first explains what each switch does, and the
second is a list of specific configurations. For more information, consult PAC24 Configuration
Quick Reference Guide, document number 200-240-0310.
In a single installation, with no options, no action is required.
In dual installations, place the DIP switches into the proper position to configure the PAC24 as the pilot, or
copilot panel.
By designating a pilot or copilot panel, the aircraft commander, or pilot, will have priority for transmissions
and intercom mode selection. Note:
Bold=Default settings (as shipped from factory)
Units are shipped as single unit configuration, 28V lighting.
PAC24 units MUST be reconfigured before any other configuration is used.
2.2.1 Disassembly and access
To access the circuit jumpers and DIP switches, remove the top cover by removing the two (2) screws at
the sides holding the cover in place.

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 2-2 Rev. 29, Sept. 2021
Figure 2-1 Cover Screw Locations
Figure 2-2 Locations
DIP Switches
Remove 2 top screws
Circuit Jumpers

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 2-3 Rev. 29, Sept. 2021
2.2.2 Single/Dual configuration jumpers J4 & J5
Single System or Pilot Audio Panel
Copilot Audio Panel
J4 ON (installed)
J4 OFF (Removed)
J5 Jumper Pins 1 & 2
J5 Jumper Pins 2 &3
Figure 2-3 Circuit Jumper Configurations: Pilot Audio Panel (left) Copilot audio panel (right).
C
H
A
S
S
I
S
J4
J5
Pilot Audio Panel
J4 Installed
J5 Pins 1 & 2
C
H
A
S
S
I
S
J4
J5
Copilot Audio Panel
J4 Removed
J5 Pins 2 & 3

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 2-4 Rev. 29, Sept. 2021
2.2.3 DIP Switch Configurations
Figure 2-4 DIP Switch positions
2.2.3.1 Pilot/Copilot Audio Panel DIP Switch Configuration
Switch
S5
2
OFF
Single
PAC24
Installation
ON
Pilot unit –Dual
Installation
ON
Copilot unit –
Dual Installation
3
OFF
OFF
ON
Table 2-1 Pilot/Copilot Dual Panel Selection Switch (S5)
2.2.4 Passenger and Expansion DIP Switch Configurations
2.2.4.1 Pass 3 / Expansion (P/N 11606) –J3, pin a configuration (S2)
As shipped, the PAC24 is 5-place intercom, and the ability to convert the system from a 5-place intercom
to use an expansion unit that will allow up to 8 places on the intercom per audio panel.
Switch
S2
3
ON
Pass 3 Mic Input
OFF
P/N 11606 Expan-
sion Power out
4
OFF
ON
S2
S3
S5
S4
1 2 3 4

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 2-5 Rev. 29, Sept. 2021
2.2.4.2 Pass 1 / Expansion (P/N 11606) –J3, pin 22 configuration (S2)
Switch
S3
1
ON
Pass 1 mic input
OFF
P/N 11606 Expan-
sion audio input
2
OFF
ON
2.2.4.3 Pass 2 / Expansion (P/N 11606) - J3, pin 23 configuration (S3)
Switch
S3
3
ON
Pass 2 mic input
OFF
P/N 11606 Expan-
sion audio output
4
OFF
ON
2.2.4.4 CVR –J3, pin 2 configuration (S2
Cockpit Voice Recorder audio output connector pin 2
Switch
S2
1
ON
CVR Output
OFF
OPEN
2
OFF
ON
2.2.4.5 14-Volt Backlighting / Swap –J3, pin 18 configuration (S4)
The installer has the option of implementing PS Engineering’s patented “Swap” function, which allows the
pilot to switch between Com 1 and Com 2 with an external switch. The Swap command is controlled
through the unused backlight input, and selected by the internal DIP switch.
Switch
S4
1
ON
14 V lighting
control
OFF
Swap switch
2
OFF
ON
2.2.4.6 28-Volt Backlighting / Swap –J3, pin U configuration (S4)
Switch
S4
3
ON
28 V lighting
control
OFF
Swap switch
4
OFF
ON
2.2.4.7 Backlight 14/28V
Switch
14 V
28V
1
On
Off
2
Off
On
3
Off
On
4
On
Off

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 2-6 Rev. 29, Sept. 2021
14 V Aircraft
28 V aircraft
Pin 18= 14 V input
Pin 18=Swap
Pin U=Swap
Pin U =28 V input
2.2.4.8 Expansion Mode (P/N 11606) / Telephone configuration (S5)
Switch
S5
1
On
Expansion Unit Present (P/N 11606 installed)
4
On
Duplex Telephone mode for Com 5
NOTE: Set both audio panels the same in a dual installation
2.2.4.9 Observer System Installation Configuration (S5)
NOTE: -0400 must be interfaced with other like part number units and are always dual installations.
When the Observer versions are used (Part Number 050-240-0400) the cockpit unit is configured as
“Crew” and the Observer station is configured as “Observer.”
Switch
S5
2
ON
Crew unit –
Observer Installa-
tion
ON
Observer unit –
Installation
3
OFF
ON
Switch
S3
1
OFF
P/N 11606 Expansion In
enabled
2
ON
3
OFF
P/N 11606 Expansion Out
enabled
4
ON
Switch
S2
3
ON
Pass Input
4
OFF
In an observer unit, jumpers J4 and J5 should be configured like a copilot's unit in dual installation.
2.2.5 DIP Switch Cross reference.
Single Installation- 28 Volt Aircraft
Single panel with Expansion (P/N 11606)
28 Volt Aircraft
SW2
SW3
SW4
SW5
SW2
SW3
SW4
SW5
1
ON
ON
OFF
OFF
1
OFF
OFF
OFF
ON
2
OFF
OFF
ON
OFF
2
ON
ON
ON
OFF
3
ON
ON
ON
OFF
3
OFF
OFF
ON
OFF
4
OFF
OFF
OFF
See
notes
4
ON
ON
OFF
See notes
J4- On/ J5- Pins 1 & 2
J4- On/ J5- Pins 1 & 2
Table 2-2 Single Audio Panel DIP switch settings

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 2-7 Rev. 29, Sept. 2021
Dual PAC24 - Pilot Panel- 28 Volt Aircraft
Dual PAC24- Copilot Panel- 28 Volt Aircraft
SW2
SW3
SW4
SW5
SW2
SW3
SW4
SW5
1
ON
ON
OFF
OFF
1
ON
ON
OFF
OFF
2
OFF
OFF
ON
ON
2
OFF
OFF
ON
ON
3
ON
ON
ON
OFF
3
ON
ON
ON
ON
4
OFF
OFF
OFF
See
notes
4
OFF
OFF
OFF
See
notes
J4- On/ J5- Pins 1 & 2
J4- Off J5- Pins 2 & 3
Table 2-3 Dual Audio Panel DIP Switch Settings without expansion
Dual PAC24 with Expansion (P/N 11606)-
Pilot Panel- 28 Volt Aircraft
Dual PAC24 with Expansion (P/N 11606)-
Copilot Panel- 28 Volt Aircraft
SW2
SW3
SW4
SW5
SW2
SW3
SW4
SW5
1
ON
OFF
OFF
ON
1
ON
OFF
OFF
ON
2
OFF
ON
ON
ON
2
OFF
ON
ON
ON
3
OFF
OFF
ON
OFF
3
OFF
OFF
ON
ON
4
ON
ON
OFF
See
notes
4
ON
ON
OFF
See
notes
J4- On/ J5- Pins 1 & 2
J4- Off/ J5- Pins 2 & 3
Table 2-4 Dual Audio Panel DIP Switch Settings with expansion
Dual PAC24 Observer (-0400)-
CREW Panel- 28 Volt Aircraft
Dual PAC24 Observer (-0400)-
Observer Panel- 28 Volt Aircraft
SW2
SW3
SW4
SW5
SW2
SW3
SW4
SW5
1
ON
OFF
OFF
OFF
1
ON
OFF
OFF
OFF
2
OFF
ON
ON
ON
2
OFF
ON
ON
ON
3
ON
OFF
ON
OFF
3
ON
OFF
ON
ON
4
OFF
ON
OFF
See
notes
4
OFF
ON
OFF
See
notes
J4 - On/ J5- Pins 1 & 2
J4 - Off/ J5- Pins 2 & 3
Table 2-5 Dual Audio Panel with Observer (-0400) Function, DIP switch settings
Dual PAC24 Observer (-0400) w Expansion (P/N
11606)- Crew Panel- 28 Volt Aircraft
Dual PAC24 Observer (-0400) w Expansion (P/N
11606)- Observer Panel- 28 Volt Aircraft
SW2
SW3
SW4
SW5
SW2
SW3
SW4
SW5
1
ON
OFF
OFF
ON
1
ON
OFF
OFF
ON
2
OFF
ON
ON
ON
2
OFF
ON
ON
ON
3
OFF
OFF
ON
OFF
3
OFF
OFF
ON
ON
4
ON
ON
OFF
See
notes
4
ON
ON
OFF
See
notes
J4- On/ J5- Pins 1 & 2
J4- Off/ J5- Pins 2 & 3
Table 2-6 Dual Audio Panel with observer (-0400) and with Expansion (P/N 11606)

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 2-8 Rev. 29, Sept. 2021
PAC24 Rear Connector
2
a
CVR Audio
No Connect
Pass 3
Expansion power
S2
22
23
Pass 1 Mic
Expansion in
Pass 2 Mic
Expansion out
S3
18
U
14V light Hi
Swap
28V light hi
Swap
S4
Expansion Active
Dual System
Copilot Unit
TEL/Duplex
S5
Logic
+5
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
Figure 2-5 DIP switches shown schematically
General Notes
•If telephone is connected, turn SW5-4 to ON for all panels. Otherwise set it to OFF
•For 14V aircraft, change SW4 1-4 to ON, OFF, OFF, ON
•For CVR output, change SW2 1-2 to ON, OFF. NOTE: IRS cannot be used
2.3 Equipment Installation Procedures
2.3.1 Mounting Requirements
The PAC24 must be rigidly mounted to the instrument panel of the aircraft structure and within view and
reach of the pilot position(s). Installation must comply with FAA Advisory Circular AC 43.13-2A. The unit
may be mounted in any area where adequate clearance for the unit and associated wiring bundle exist.
Avoid installing the audio panel close to high current devices or systems with high-voltage pulse type out-
puts, such as DME or transponders.
NOTE: The mounting hole configuration for the PAC24 is identical to the
KMA-24H -71 Audio Selector Panels.

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 2-9 Rev. 29, Sept. 2021
2.3.2 Cooling Requirements
Forced air cooling of the PAC24 is not required. However the unit should be kept away from heat produc-
ing sources (i.e. defrost or heater ducts, dropping resistors, heat producing avionics) without adequate cool-
ing air provided. Outside, ram air cooling of the unit is not permitted, and may result in damage.
2.3.3 Mounting Rack Installation
Remove the unit from the mounting tray by unscrewing the 3/32" hex-head screw that is between the RCV
and XMT legends. Use caution to avoid hitting the photo-detector lens. Carefully slide the unit free of the
tray. Set the unit aside in a safe location until needed. Install the tray using six clip nuts (475-630-0002),
and six FHP 6-32 x ½" screws (475-632-0012). The audio selector panel must be supported at front and
rear of the mounting tray.
2.3.4 Tray and Connector Assembly
The unit connector mates directly with the circuit board in the PAC24. The connector is a Molex crimp-
type, and requires the use of a Molex hand crimp tool, EDP P/N 11-01-0203, CR6115B (or equiv.). The
connector is mounted to the unit tray with #4-40 screws (475-440-0007), from the inside of the tray. Ensure
that proper strain relief and chafing precautions are made during wiring and installation, using the cable
clamp (625-001-0002). Secure the ground bar (430-630-0002), if desired using, #6-32 nuts (475-632-0003)
and #6-32 lock nuts (475-632-0004).
2.4 Cable Harness Wiring
Referring to the appropriate Appendix, assemble a wiring harness as required for the installation. All wires
must be MIL-SPEC in accordance with current regulations. Two- and three-conductor shielded wire must
be used where indicated, and be MIL-C-27500 or equivalent specification. Proper stripping, shielding and
soldering technique must be used at all times. It is imperative that correct wire be used.
Refer to FAA Advisory Circular 43.13-2A for more information. Failure to use correct techniques may
result in improper operation, electrical noise or unit failure. Damage caused by improper installation will
void the PS Engineering warranty.
2.4.1 Noise
Due to the variety and the high power of radio equipment often found in today's general aviation aircraft,
there is a potential for both radiated and conducted noise interference.
The PAC24 power supply is specifically designed to reduce conducted electrical noise on the aircraft power
bus by at least 50dB. Although this is a large amount of attenuation, it may not eliminate all noise, particu-
larly if the amplitude of noise is very high. There must be at least 13.8 VDC present at the bottom connect-
or, pin 25, of the PAC24 for the power supply to work in its designed regulation. Otherwise, it cannot ade-
quately attenuate power line noise. Shielding can reduce or prevent radiated noise (i.e., beacon, electric
gyros, switching power supplies, etc.) However, installation combinations can occur where interference is
possible. The PAC24 was designed in a RFI hardened chassis and has internal Electromagnetic Interfer-
ence (EMI) filters on all inputs and outputs.
Ground loop noise occurs when there are two or more ground paths for the same signal (i.e., airframe and
ground return wire). Large cyclic loads such as strobes, inverters, etc., can inject noise signals onto the air-
frame that are detected by the audio system. Follow the wiring diagram very carefully to help ensure a min-
imum of ground loop potential. Use only Mil Spec shielded wires (MIL-C-275000, or better).Under no
circumstances combine a microphone and headphone wiring into the same shielded bundle. Always use a
2- or 3-conductor, shield wire as shown on the installation wiring diagram.
Radiated signals can be a factor when low level microphone signals are "bundled" with current carrying
power wires. Keep these cables physically separated. It is very important that you use insulated washers to
isolate the ground return path from the airframe to all headphone and microphone jacks.
Adding a high-performance audio control system, particularly in conjunction with high-performance active
noise canceling headsets, cannot improve on older avionics that were designed for cabin-speaker use. PS

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 2-10 Rev. 29, Sept. 2021
Engineering makes no claim that the audio panel will provide a noise-free audio quality under all installa-
tion conditions, particularly with older avionics.
2.4.2 Existing KMA 24H Installation
If the installation replaces a KMA-24H (series –71), and it is properly installed and wired, no other changes
are required except for removal of the keying pin. Other options not present in the KMA24H, such as en-
tertainment or “Swap” may require additional wiring. KMA-24H Speaker Power (J3, pin 7) is not required.
NOTE:
Many installation use external switching to provide crewmember isolation. These can usually be
eliminated. See below for details.
2.4.2.1 Single KMA24H -71 Installation
If the switch, labeled Isolate/Normal/Private is installed, the Primary/Secondary headphone switch should
be maintained. However, the connection to P241, Pins 21, 24, and Y should be removed.
2.4.2.2 Dual KMA24H -71 Installation
In a dual KMA24H-71 installation, we recommend that the ISO/Normal/Private switches be removed.
These switches apply a ground to logic inside the KMA24H.
THE CONNECTIONS BETWEEN THE AUDIO PANELS MUST BE LEFT INTACT. This includes Pins
V to V (Key Enable), 21 to 24 (Isolate /Isolate 22) and Y to Y (Private). PS Engineering uses these lines for
data bus communications between panels.
2.4.3 Power
The PAC24-Series are compatible with both 14 and 28 Volt DC systems. A three (3) Amp breaker is re-
quired. Power and ground wires must be a #18 AWG pair. Connect airframe power ground to J3 Pin 25
only. No dropping resistors are required.
2.4.4 Communications Push-to-Talk (single panel installation)
Unless the system is in split mode, only the person who presses their transmit PTT switch will be heard
over the radio. If the pilot and copilot both use the PTT, only the pilot position has access to the radio. The
pilot position will have PTT control regardless of the copilot PTT when the PAC24 is in the OFF/EMG
mode.
2.4.4.1 Communications Push-to-Talk (Dual Panel Installation)
The PAC24 automatically senses if the other audio panel is transmitting. If communications transceivers
selected for transmit are different (Com 1 pilot, Com 3 copilot), both panels will allow simultaneous, dual
transmission (split mode). If the same radio has been selected for transmit on both audio panels, the pilot
mic will have priority, and the copilot will not transmit.
2.4.5 Audio Panel interface
The PAC24 is designed to interface with standard aircraft avionics, and presents a 500receiver imped-
ance. For best results, a twisted-shielded cable is recommended from the avionics audio source to the audio
panel, with the shield grounded at the audio panel end.
Some avionics do not provide a separate audio low, and may introduce additional electrical noise into the
system. For best results, connect the audio low from the audio panel to the radio ground, using one conduc-
tor of the twisted-shielded cable.
2.4.6 Transmit Interlock
Some communications transceivers use a transmit-interlock system. To fully utilize the Split Mode feature,
this function must be disabled. Consult that manufacturer's installation manual.

PS Engineering
PAC24 Series Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-240-0010 Page 2-11 Rev. 29, Sept. 2021
2.4.7 "Swap" Mode
When a momentary, normally open, push-button switch is connected between pin U (14 V) or 18 (28V
lighting) on the unit connector and aircraft ground, the user can switch from Com 1 to 2 to 3 etc. by de-
pressing this switch without having to change the mic selection. This yoke-mounted switch eliminates the
need to remove your hands from the controls to change transceivers.
NOTE: Swap mode is active if the proper DIP switch selection is made internally to the unit.
2.4.8 Backlighting
The PAC24 has an automatic dimming of the pushbutton annunciator LEDs and marker lamps controlled
by a photocell. Control of the unit backlighting is through the aircraft avionics dimmer. Connect the dim-
mer control line to J3 pin 18 for 14-volt systems, and to J3 pin U for 28-volt systems. Pin 17 is light
ground.
If an external dimmer control is not used, a constant low-level back light illumination can be established for
nighttime viewing. Pin 18 or U (depending on system voltage) must be tied to power (J3, pin 25) for the
back lighting system to work. The photocell mounted in the unit face will automatically adjust the intensity
of the push-button annunciator LEDs.
2.4.9 Unswitched inputs
J3, pin 10 is the unswitched input number 1 and J3 pin 14 is unswitched input 2. These inputs are presented
to the pilot and copilot regardless of the audio configuration, and will always mute the entertainment in-
puts. These 510Ω inputs can be used for altimeter DH audio, GPS waypoint audio, autopilot disconnect
tones, or any other critical audio signal.
NOTE: In installations where an expansion unit is NOT used, the passenger and copilot audio output is
paralleled (J1, pin b). Therefore, unswitched audio will be heard by the passenger(s). Use an expansion
unit, P/N 11606, or 11606R (remote) to isolate passenger audio from unswitched alert audio.
2.4.10 PA Mute (J3, Pin 8)
Pin 18 of J3 is a TTL logic output that is pulled low during PTT operation. This serves as an input to exter-
nal public address system to prevent feedback during transmissions.
2.4.11 Public Address (J3, Pin B)
When the Speaker mode switch is in the PA mode, and the pilot’s PTT is activated, his voice is heard over
the PA speaker output on J3, Pin B. The copilot can continue to use the selected com.
In a dual installation, both the pilot and copilot panels can be connected to separate PA Speakers, for in-
stance, one ramp hailer, and one public address speaker.
NOTE: Connecting two audio panels to a single speaker for cockpit and/or cabin address
can result in damage to the audio panel.
2.4.12 Intercom wiring
See Appendices for intercom connection configurations. It is critical to the proper operation of this system
to have this connector wiring made in accordance with these diagrams. Use 2- and 3-conductor, MIL-spec
cable as shown. Connect the shields at the audio panel end only, and tie to the audio low inputs as shown.
2.4.12.1 Push to talk intercom
The PAC24 can be used as an IntelliVox® intercom, or, as a keyed intercom. Switching J3 pin W to
ground will inhibit the IntelliVox® and the intercom squelch will not open until the ICS PTT switch is ac-
tivated.
The following pins are used to control the intercom when PTT ICS is desired. Pin 11 must be grounded
through a momentary switch for the pilot to talk on the intercom (with W also grounded). Pin M must be
grounded through a momentary switch for the copilot to talk on the intercom (with W also grounded).