speaker system. Headphone audio is independent of
the position of these switches.
(4) AUDIO EMER / NORM Switch. A two-
position switch, placarded AUDIO EMER / NORM,
located on the pilot's side of the audio control panel,
provides a means of selecting a secondary audio
source in the event of a failure disabling both audio
amplifiers. When the switch is set to the EMER
position, power is removed from both audio amplifiers
and audio is routed directly from the receivers to the
headphones. Speaker audio and cabin public address
will be inoperative. When the switch is set to the
NORM position, audio is routed normally through
amplifier to speakers or headphones.
(5) INTPH/OFF Switch. The pilot and copilot
are each provided with a two-position switch placarded
INTPH OFF, located on their respective sides of the
audio control panel, which controls the operation of
their voice-actuated interphone systems. When the
switch is set to the INTPH position, the headset
microphone of the pilot at that station will be actuated
whenever the microphone is spoken into, and will be
heard by the other pilot. When both the pilot's and
copilot's INTPH switches are ON (up), continuous
voice-actuated intercom is available. When the switch
is set to the OFF position, voice-actuated intercom
operation is discontinued. The interphone switch is
connected through the speaker OFF switch to disable
the hot interphone when the speaker is ON.
(6) VOICE / BOTH / RANGE Switch. The
pilot and copilot are each provided with a three-
position switch placarded VOICE / BOTH / RANGE,
located on their respective sides of the audio control
panel, which controls selection of ADF voice or range
filtering. When the switch is set to the VOICE position,
identification. When the switch is set to the RANGE
position, the 1020 Hz range tone is enhanced, and
voice is suppressed.
(7) CABIN ADF Switch. A two-position
switch placarded CABIN ADF 1 / OFF / ADF 2,
located in the center of the audio control panel,
controls the selection of ADF audio which is routed to
the four cabin speakers. When set to the ADF 1 or
ADF 2 position, audio from the respective ADF 1 or
ADF 2 receiver is channeled to the cabin speakers.
When set to the OFF position, ADF audio is removed
from the cabin speakers.
(8) Pilot and Copilot Public Address Volume
Control. This knob, placarded PA, adjusts audio
volume to the four cabin speakers.
(9) Pilot and Copilot Headphone Volume
Control. This knob, placarded PH, adjusts audio
volume to headphones.
Volume Control. This knob, placarded SPKR, adjusts
audio volume to cockpit speakers.
(11) MKR / BCN / VOL Control. The marker
beacon volume control knob, placarded MKR BCN 1 &
2, VOL, is used to control the audio volume from the
marker beac on receivers.
(12) MKR BCN HI / LO / TEST Switch. A
three-position switch, placarded MKR BCN 1 & 2, HI /
LO / TEST, located on the audio control panel, selects
sensitivity of the marker beacon receivers and test
function. When the switch is set to the HI position, the
marker beacon receivers are set to high sensitivity.
When the switch is set to the LO position, the marker
beacon receivers are set to low sensitivity. When the
switch is held in the spring-loaded TEST position, the
marker beacon annunciator lights will be illuminated.
(13) Compass System Selector Switch. A
HEADING switch placarded
SYSTEM ON COMPASS 1 / NORM / ALL SYSTEMS
ON COMPASS 2 is located in the center of the audio
control panel. This switch allows the selection of
heading data to be all systems on compass 1 or all
systems on compass 2 or norm, pilot on compass 1
and copilot on compass 2.
(14) DME HOLD Switch. A push-on/push-off
switch, placarded DME HOLD PUSH/SW, located on
the audio control panel, controls selection of the DME
hold function. When the DME HOLD switch is pushed
to the on position, the DME/TACAN distance
frequency in the DME/TACAN receiver-transmitter will
be held constant regardless of the frequency selected
on the NAV 1 control unit. The DME HOLD switch will
illuminate when the DME hold function is selected, and
will be extinguished when DME hold function is
deselected. The DME HOLD switch is disabled in
TACAN mode or if the FMS is controlling the DME.
(15) DME/TACAN Volume Control. This
knob, placarded DME/TAC, located on the pilot's side
of the audio control panel only, adjusts DME or
TACAN audio volume.
(1) Turn-on Procedure. Electrical power is
applied to the audio control panel whenever electrical
power is applied to the aircraft and the AVIONICS
MASTER POWER SWITCH is set to the ON position.