the AVIONICS MASTER POWER switch to the EXT PWR position allows avionics isolation from DC GPU power to
be overridden, de-energizing the avionics power relay, and applying power to the avionics equipment from the DC
b. Single-Phase AC Power. Two static inverters supply 400 Hz single-phase 115 volt and 26 volt AC electrical
power to the avionics equipment. During normal operation, the #1 inverter supplies 115 volts AC and 26 volts AC
power to the #1 avionics systems and the #2 inverter supplies AC power to the #2 avionics system. If either inverter
fails, the total single-phase AC electrical load is shifted to the remaining inverter automatically unless a ground fault
exists. Either inverter is capable of supplying the entire AC electrical load. AC power from the inverters is routed
through fuses located in the nose avionics compartment. The single phase inverters are controlled by two switches
placarded #1 and #2 1ø INVERTER - ON , located on the overhead control panel (Fig. 2-13).
c. Three-Phase AC Power. Three phase AC electrical power for operation of the inertial navigation system and
mission avionics is supplied by two 3000 volt-ampere, solid state, three phase inverters. The three phase inverters
are controlled by two three-position switches placarded 3ø AC CONTROL, #1 and #2 INV, RESET- ON - OFF ,
SECTION II. COMMUNICATIONS
The communications equipment group consists of an intercom system connected to individual audio control panels
for the pilot and copilot which interface with VHF, ARC-210, BU VOW, VHF-FM transceivers, and provide reception of
audio from VOR, localizer, marker beacon, TACAN/DME, and ADF receivers. An onboard Radio Control Unit (RCU),
CDU 7000, remotes through MCDUs provides crew with radio management. Operate the RCU in accordance with
the vendor s operator manual.
3-5. MICROPHONES, SWITCHES, AND JACKS.
Headset microphone boom and oxygen mask microphones can be utilized in the aircraft.
a. Control Wheel Microphone Switches. The pilot and copilot are each provided with bi-level microphone
switches placarded MIC, INTPH - XMIT , located behind the outboard handgrip of their respective control wheels
(Fig. 2-29). When the control wheel microphone switches are depressed to the irst level (INTPH position), voice
audio signals from the respective microphone are routed to the intercom system (the position of the transmitter-in-
tercom selector switch is disregarded). When the control wheel microphone switches are depressed to the second
level (XMIT position), voice audio signals from the respective microphone are routed to the transmitter selected by
the transmitter-intercom selector switch (located on the respective audio control panel, Fig. 3-1).
b. Cockpit Floor Foot-Operated Microphone Switches. The pilot and copilot are each provided with a foot-
operated microphone switch, placarded MIC , located on the cockpit loor, forward of their respective seat positions.
Depressing the foot-operated microphone switches routes audio signals to the device selected by the transmitter-
intercom selector switch located on the respective audio control panel (Fig. 3-1).
c. Microphone Jack Selector Switches. Two switches, placarded MIC, HEADSET OXYGEN MASK , located
on the left and right sides of the instrument panel (Fig. 2-22 and 2-23), provide a means of selecting which micro-
phone jack is connected to the audio system. When the pilot or copilot s switch is set to the HEADSET position, the
headset jack is connected to the respective audio system. When set to the OXYGEN MASK position, the oxygen
mask jack is connected to the respective audio system.
3-6. AUDIO CONTROL PANELS.
a. Description. Separate identical audio control panels (Fig. 3-1), located on the left and right subpanels (Fig.
2-11), and are provided for the pilot and copilot. Each audio control panel is powered by its respective 2-ampere
circuit breaker placarded AUDIO PILOT or AUDIO COPIL , located on the overhead circuit breaker panel (Fig. 2-12).