3-6. Interphone System.
affects intercom volume only. It does not affect volume
of other audio inputs selected with the pushbuttons.
a. Description. Identical audio control panels are
provided for the pilot and copilot. The controls and
(2) Speaker audio select buttons. Selects
switches on each panel provide for audio reception of
desired audio inputs to be heard on the speakers.
interphone, communication, navigation audio signals,
and a choice of transmission on VHF, UHF, and HF (if
(3) MIC SELECT switch. The MIC SELECT
installed). Cabin speakers and crew headphones are
switch performs several functions. It routes microphone
utilized for audio reception. Aircraft power for speaker
audio and keying to the appropriate system and switches
and headphone isolation amplifiers is derived from
the speaker amplifier output to the appropriate speaker.
separate sources to provide a high degree of audio
In the 1, 2, 3, or 4 positions, microphone audio and
integrity. The power is routed through 3-ampere circuit
keying are routed to the appropriate transceiver and the
breakers placarded SPKR 1 and SPKR 2, and 1-ampere
speaker amplifier output is connected to the cockpit
circuit breakers placarded PHONE 1 and PHONE 2,
speakers. In the PA position, microphone audio is
located on the lower right sub panel.
routed to the speaker amplifier. The speaker amplifier
output is connected to the passenger address speakers.
b. Audio Panel (KMA 24H).
The controls and
In the INT position, microphone audio is routed to the
switches on the KMA 24H audio control panel (fig. 3-1)
intercom output. In INT, 1, 2, 3, or 4 positions, any audio
provide for selection and volume control of interphone,
output selected on the top row of pushbuttons will be
communication, and navigation audio signals.
heard through the cabin speakers. Keying causes the
output audio to be muted and the sidetone audio to be
c. Controls and Functions.
(1) INT VOL control. Volume of the intercom
Permits the flight crew to
input is controlled by the INT VOL control. This control
INT VOL switch
SPEAKER audio select buttons
MIC SELECT switch
PHONE audio select buttons
Figure 3-1. Audio Control Panel
3-2 Change 5