King Kma 20 Audio Panel Manual

As instructors we are sometimes quite guilty of assuming “everyone knows that”, whatever “that” may be.Just a simple question from a student however can quickly make us realize it’s a false assumption.So it was a question from a student concerning the operation of an audio panel made me realize that it is probably worth offering some explanation about its operation.

The audio panel in question was the KMA 24, probably one of the most common audio panels found in planes.

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Bypass the KMA 26’s audio amplifier and directly connects Com 1 to the pilot’s microphone and headphones. This provides a fail-safe method of communication should the unit fail. The “PA” position may be selected when the aircraft is configured with the KMA 26 driving a dedicated passenger address speaker. The KMA 26 has an “Auto Com”. Bendix/King KMA28 Audio Amplifier/Intercom/Marker Beacon Receiver that you use insulated washers to isolate the ground return path from the airframe to all headphone and microphone jacks. 2.4.2 Existing KMA-24 Installation If the installation replaces a KMA-24 (series –00, -01, -02 or -03), the existing 44 pin connector can be used for the.

King Kma 20 Audio Panel Manual Youtube

In an overall view, the KMA 24 audio panel has two rows of buttons, flanked on the left by marker beacon lights and on the right by a rotary knob whose principle function allows the user to select COM 1 or COM 2.The top row of buttons directs the selected audio output to the speaker in the aircraft.The bottom row of buttons directs the selected audio output to your headset.

Marker beacon lights are used in many ILS instrument approaches.If the ILS approach has marker beacons (not all of them do), the most common ones are the outer marker (the blue light marked “O”) and the middle marker (the amber light marked “M”).The inner/airway marker (the white light marked “A”) is generally only installed at major airports.Marker beacons emit a 75-Mhz signal.When the aircraft passes over an outer marker, the blue marker beacon light is seen.A middle marker beacon illuminates the amber marker beacon light.In addition, an audible tone may be heard.If you want the audible signal to come through the speaker, press MKR (#9) on the top row of buttons.If you want it to come through your headset, press MKR on the bottom row of buttons.

The 75 Mhz signal transmitted by the marker beacons is a carrier frequency.This carrier frequency is modulated into a 400 hz, 1300 hz or 3000 hz signal for the OM, the MM, and the IM respectively.

TST - test the marker beacon lights.Pressing this button causes all the marker beacon lamps to illuminate.SENS - the button just to the right of the amber marker beacon lamp selects the sensitivity of the marker beacons.HI allows the marker beacon signal to be detected approximately one mile before passing over the beacon.At this point, if you had HI sensitivity selected, you would want to switch to LO sensitivity.A word of caution concerning the TST button.Bendix King notes that the TST button should not be pushed when the autopilot is coupled on an ILS approach.Some autopilots, including Bendix King models, use the marker beacons to change the sensitivity of the autopilot.Next to the “O” marker beacon lamp is a photoelectric cell which controls the brightness of the marker beacon lamps.
TEL – controls audio for a radio telephone.Alternately some KMA 24 audio panels replace the TEL function with HF, for operation with a high frequency transceiver.Note that this function, either TEL or HF, must also be selected on the rotary knob on the right side of the audio panel.
1 COM – controls audio received from COM 1 communications radio.Again, the top row button directs output to the aircraft speaker, and the bottom row button directs it to your headset.
COM 2 – controls audio received from COM 2 communications radio.
1 NAV – controls the audio received from the NAV 1 radio.This includes any weather information, such as HIWAS as well as the Morse code IDENT.Many nav radios have a switch on the radio for IDENT.This must be selected in addition to selecting either speaker or headset for the audio.
NAV 2 – ditto for the NAV 2 radio.
DME – allows you to hear the Morse code identifier for any DME that is co-located with VOR or localizer stations.Most DME receivers have the ability to enter a frequency separately from the nav radios.However the most common method of operation is to remote the DME receiver to either nav 1 or nav 2.
MKR – allows you to hear the marker beacon audio signals.
ADF – allows you to hear the Morse code identifier of an NDB station.During an NDB approach, most instructors teach their students to keep the Morse code identifier for the NDB on during the entire approach to verify integrity of the signal.Unlike VOR receivers, ADF receivers do not display an OFF flag, so the Morse code is the only way to ensure the data being received by the ADF receiver is valid.
AUTO – this is probably the most confusing button for pilots when they first work with the audio panel.The rotary switch on the right side of the KMA 24 can be set for either COM 1 or COM 2.The rotary switch controls the transmission frequency.So if you have COM 1 selected with the rotary switch, when you push the transmit button, you are transmitting on COM 1.The AUTO button allows you to automatically slave the received audio information to whichever frequency you have selected with the rotary switch.By pressing the AUTO button in the bottom row (headset), you will automatically hear the transmissions from either COM 1 or COM 2, depending on which one has been selected by the rotary switch.So with AUTO selected, you may switch back and forth between COM 1 and COM 2 with the rotary switch without having to reselect COM 1 or COM 2 using the push buttons.If you desire to hear audio from the other com radio, you may do so by simply pressing the appropriate button for either speaker or headset.For example you are listening and transmitting on COM 1 but would like to listen to ATIS at the same time.You may do this by putting the ATIS frequency in COM 2 and pressing the COM 2 button for either speaker or headset.Warning – it can be confusing to try to listen to two frequencies at the same time.
The rotary switch on the right side is used to select the desired transmitter for the cockpit microphones.COM 1 and COM 2 have been previously discussed.The INT position selects cabin intercom.This allows the crew to address the passengers over the cabin speaker.The EXT position allows the crew to address people on the ramp through an external ramp hailer speaker, if one is installed.

In putting this discussion together, I found a good pilot guide to operation of the KMA 24 audio panel on the Bendix King website.It is a downloadable pdf file, and the web address is

Pilot Guide to the KMA 24 Audio Panel

The PMA7000 series audio panel not only provides a great set of capabilities, it also lends itself nicely for upgrading an existing Bendix/King KMA24 audio panel. The PMA7000B is KMA24 pin compatible, making the cost of the upgrading less expensive. None of the existing wires going to the KMA24 have to be disturb, only a new intercom wire harness has to be built, reducing the amount of installation time.

With our renown 6-place IntelliVox® automatic Voice Operated Relay (VOX) intercom system, adjusting a squelch circuit is a thing of the past. And with over 20+ years of field experience, find out just how easy it is to forget you are even using an intercom, it just works! No more clipping or missed syllables.

The PMA7000B provide 3-com capability with the option to easily convert Com 3 to a full duplex cellular telephone interface. It also has our pioneered 'Split Mode'. This allows the pilot to be on Com 1 while the copilot is on Com 2, freeing up the pilot to work with ATC while the copilot gets weather information or finds out just where the lowest fuel cost is on the field while still in the air.

Check list of capabilities:

IntelliVox® automatic VOX system with individually gated microphone
6 Place hi-fi stereo intercom with Soft Mute™
2 music mute modes: Mute On and Mute Off (ICS button)
Built-in Marker Beacon Receiver
Hardwired Satelite Telephone connection (in lieu of Com 3) which provides provides dedicated On/Off hook switches for unprecedented flexibility
Split mode for dual audio panel capability
2 hi-fidelity stereo music source inputs
3 isolation modes - Pilot Isolate, All, and Crew
4 unswitched inputs
Selectable music muting for passengers
Selectable special intercom mode with 'Alternate Intercom Mode'
RAM (Radio Active Mute) eliminates constant back ground noise from radio static
2-year Pro-Support Warranty

King Kma 20 Audio Panel

The only knob that is on the panel is a concentric volume control for the Crew and Passengers intercom volume. The all push button controls of the PMA7000B allows for easy selection of Coms and other Nav aids.

The PMA7000B has four un-switched and un-muted inputs. This adds flexibility when installed with today's advanced warning systems, like Skywatch or TAWS.

Here are the steps it takes to replace a KMA24 with a PMA7000B:

Step 1 - remove KMA24 from tray
Step 2 - remove the connector from KMA24 tray
Step 3- remove tray
Step 4 - install PMA7000B tray
Step 5 - install connector in PMA7000B tray
Step 6 - install PMA7000B into tray

BUT.........

You will not have any intercom functions until that portion of the install is completed.

That's why there is second connector. This connector must be wired by your avionics shop that will provide all of the intercom functions, telephone interface, and music inputs.

The PMA7000B is plug and play with the original PMA7000M-S, the PMA6000M-S, and the KMA28.