Part# 11-02791
MFR Model# SPA-400
DescriptionPart Number
SPA-400 S THRU 4 WAY (STANDARD)11-02791


The Intercom That Set The Standard
Sigtronics pioneered the voice activated intercom market in 1974 and continues to deliver value and performance today in the 4 or 6 place FAA TSO approved SPA-400 / 600 intercom series. With fail safe features that allow pilots to always hear the radio even if the intercom is off, and radio priority that assures ATC only hears the crew member transmitting, the SPA intercom series is the standard by which all others are judged.

Individual Mic Bias Allows
The Use of Different Brands of Headsets

General aviation headset microphones draw power from the intercom or radio mic line. Some poorly designed intercom systems hook all the headsets to one mic line so that all the headsets must share the same power. Because different headsets have different power requirements, one headset may draw just enough power to work but there may not be enough power left over for any of the other headsets to function. With this type of design two identical headsets will work most of the time but get different types and models then you will have a problem. The only way to fix this is to modify or replace the intercom system with one that uses separate mic input lines. All Sigtronics intercom systems use separate mic input lines and do not have this problem.

Compact Size
Choose either rectangular (horizontal or vertical) or circular faceplate mounting configuration to fit anywhere in the cockpit. With a compact 2.5" x 1" sized panel, the SPA system will easily fit in the tightest panels. All installation hardware including jack kit and pre-wired harness are included.

High Noise Environment N Series
The SPA-400N / 600N FAA TSO approved High Noise Environment Intercom Series is designed specifically for experimental, ultralights, warbirds, helicopters, and other high noise aircraft. Push to intercom as well as voice activated intercom is available as desired. Tested by Sigtronics at ambient noise levels of between 115-120 decibels, the SPA-400N / 600N outperformed all other intercoms on the market, panel mounted as well as portable.

California Prop 65 Warning Symbol

WARNING: Cancer and Reproductive Harm - www.P65Warnings.ca.gov.


  • FAA TSO approved.
  • Pilot fail safe feature allows pilot to always hear radios.
  • Works with all brands of General Aviation headsets.
  • Reversible face plate included for vertical or horizontal mounting.
  • Radio priority assures that ATC hears only the crew member transmitting.
  • Installation hardware included, including jack kit & pre-wired harness.


  • Size:4" x 2.5" x 1"
  • Weight Unit: 4.5 oz.
  • Weight Jacks & Harness: 5.5 oz.

Technical Data

Technical Information in PDF
Installation and
Installation and Operating
Installation and Operating
Installation and Operating
Installation and Operating
Panel Template
Radio Specific

Figure 4 installation drawing modification for specified radios.

For Apollo SL-40 Radio
For Com 120 Radio
For Garmin GNC250/XL Radio
For ICOM A-200 Radio
For ICOM A20, A21 Radio
For ICOM A3, A6 , A22, A24 Radios
For King KA 134 Audio Panel
For King KMA 20 Audio Panel
For King KY 97A Radio
For Microair 760 Radio
For Narco MK12D Radio
For U-174 / U Headset Jacks
It allows pilot and co-pilot to transmit and receive on the aircraft radio and intercom between themselves, while back passengers can have a separate conversation without interrupting the front two.
Panel Mount Intercom Transmit Sidetone Modification Circuit Board 1528, (SPA-400 S/N 6069006 to Current & SPA-600 S/N 1102528 to Current)
Panel Mount Intercom Transmit Sidetone Modification Circuit Board 1440, (SPA-400 S/N 6053486 to 6069005 & SPA-600 S/N 1101839 to 1102527)
Sidetone Modification

(Out of Production)
Panel Mount Intercom Transmit Sidetone Modification Circuit Board 1092-4, SPA-400 Panel Mount, S/N 61960 to 6053485
Sidetone Modification

(Out of Production)
Panel Mount Intercom Transmit Sidetone Modification Circuit Board 1092-3, SPA-400 Panel Mount, S/N 60975 to 61959
Sidetone Modification

(Out of Production)
Panel Mount Intercom Transmit Sidetone Modification Circuit Board 1092-2, SPA-400 Panel Mount, S/N 60500 to 60974
Sidetone Modification

(Out of Production)
Panel Mount Intercom Transmit Sidetone Modification Circuit Board 1092, SPA-400 Panel Mount, S/N 60001 to 60499.
This modification is used when a Sigtronics SPA Intercom is connected to a radio or audio panel that has a low impedance headphone output (less than 100 ohms).
Installation Instructions for use on Sigtronics Panel Mount Intercom Systems
This modification applies to a Sigtronics SPA-400/600 or ST-400 / ST-600 installations.
Add pilot isolate to a SPA-400 / SPA-600 Intercom.
Music input options for Sigtronics SPA panel mount intercoms.
Instructions designed to assist avionics technicians in diagnosing commí radio transmit problems following intercom installation.
Helpful Hints
Communicating in Unusually High Noise Environments
  • Frequently Purchased With
  • Customers Also Viewed


Replaced a previous model just like it it worked as expected

Charles K Verified Purchase


September 26, 2023

Captain’s side kept cutting out last year and this year the co-pilot’s side kept cutting out. With the new Sigtronics intercom controller the issue was significantly reduced but on occasion the co-pilot’s side still cuts out. However there was significant improvement

Rick W Verified Purchase


July 20, 2023

Perfect and the price is right

David S Verified Purchase


June 4, 2023

Works great

Thomas P Verified Purchase


November 9, 2022

I am pleased with the product and look forward to many hours of clear clean communications in the cockpit.

April 23, 2020

Great customer support. A 5min call with Dino, to troubleshoot what turned out to be a small issue, saved ton of time and money. Thanks!

David R
October 10, 2017


Please note, Aircraft Spruce's personnel are not certified aircraft mechanics and can only provide general support and ideas, which should not be relied upon or implemented in lieu of consulting an A&P or other qualified technician. Aircraft Spruce assumes no responsibility or liability for any issue or problem which may arise from any repair, modification or other work done from this knowledge base. Any product eligibility information provided here is based on general application guides and we recommend always referring to your specific aircraft parts manual, the parts manufacturer or consulting with a qualified mechanic.

Q: Dose the SPA-400N include headphone jacks and wiring harness?

Yes, jack kit and pre-wired harness are included with the installation hardware.

Q: Is this SPA-400 S THRU 4 WAY (STANDARD) part # 11-02791 TSO approved and can it work with 2 place C150?

Yes, this intercom is FAA TSO approved for use in certified aircraft.

Q: Can I use one of the passenger mic inputs for my iPad? Are the impedence and gain levels for an iPad audio out the same as aircraft headsets so I can make a direct connection?

No the intercom will not allow this.

Q: Will an SPA-400S work with an existing TKM MIchel Radio(MX170C)?

The intercom does not have specific requirements for audio being fed through. As long as it is wired correctly, you will not have any issues.

Q: Will this work with an ICOM-A220? This radio has a built in intercom but it doesn’t function very well and I’d like to use this one instead.

Yes, as long as it is wired correctly, it will work.

Q: Does the SAS-640 support 6 place communication intercom (meaning 6 individual people can communicate on this system)?

Yes, that is correct.

Q: I have a SPA 400 that is on the outs. It is 30+ years old. have things changed or will this wiring harness be plug and play?

The harness will be plug and play, it's the same

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