Navigation Selector Switches
(a)
The navigation selector switches are rotary/pushbutton switches. These switches are used to select the navigation system for monitoring. Any number of the switch may be selected at the same time permitting the monitoring of more than one system. Clockwise rotation of the switch increases the volume level for monitoring. Counterclockwise rotation of the switch decreases the volume level.
BOOM/MASK Switch
(a)
The BOOM/MASK select switch is a two-position locking toggle. The switch connects the boom mic (headset) or the mask (oxygen mask) to the input.
(b)
When the oxygen mask is selected, the flight deck speakers cannot be muted.
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(6)
AIRPLANES WITH ASP P/N -20, -40, -60, -61, -64;
ALT/NORM Switch
(a) ALT/NORM mode select switch must be set in the NORM position to permit operation of the panel control. In the ALT position, the MIC selection assume a fixed configuration consistent with an emergency mode regardless of the selection made. The captain's or observer's PTT will then key VHF-1 and the first officer's PTT will key VHF-2. When in the ALT position, the volume control is preset.
(7)
V-B-R Filter Switch
(a) The V-B-R filter switch control filtering of the received navigation system audio. In the V (Voice) position, only voice audio will be heard. In the R (Range) position, only range audio (Morse code identifier) will be heard. In the B (Both) position, both voice and range audio will be heard.
(8)
AIRPLANES WITH ASP P/N -60, -61, -62, -64;
SPKR switch
(a) The SPKR switch is the off-on/volume control for the interphone speaker. This control is not used on the observer audio selector panel.
3. AIRPLANES WITH DIGITAL AUDIO CONTROL SYSTEM; Remote Electronics Unit (Fig. 3)_______________________
A. The remote electronic unit (REU) is a digitally controlled, multiplexed audio management unit. The REU manages the communication between the flight deck stations, service and flight interphone, and all related communication, radio, navigation, and recorder system. The REU determines which selections have been made on the ASP, and then sends appropriate signals to the selected systems.
B. The REU contains:
(1)
Three identical station cards for captain, first officer and observer. The station cards provide response to inputs from three audio selector panels.
(2)
One audio accessory unit (AAU) card which contains circuitry for an altitude alert warning tone, flight and service interphone, and various audio accessory functions.
(3)
One mother board which contains and provides interconnection for the captain's, first officer's and observer's station cards and AAU card.
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C. The outside of the REU case contains several screw adjustments. These are designed for in-shop test station adjustment only and should not be adjusted on the airplane.
D. Power to the REU is 28V dc dual power sources (battery bus and Bus
No. 2). The REU provides dc power to the ASPs.AIRPLANES WITHOUT DIGITAL AUDIO CONTROL SYSTEM; Audio Accessory Unit
____________________
A. The audio accessory unit (AAU) contains circuitry necessary to interface together with various interphone systems, the PA system, and various call system. The AAU manages the communication between the flight deck stations, service and flight interphone, and all related communication, radio, navigation, and recorder system. The AAU determines which selections have been made on the ASP, and then sends appropriate signals to the selected systems.
B. The front panel adjustments on the face of the audio accessory unit are
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