AIRPLANE
OPERATIONS
MANUAL
NAVIGATION AND
COMMUNICATION
JUNE 28, 2002
2-18-22
Page
1
Code
04
THIRD VHF COMMUNICATIONS SYSTEM
The airplane may be equipped with a third VHF communications
system. All functions of the Honeywell RC-833/853 System are
controlled by the RMU and by the CMU, if installed.
The active frequency will appear in the third COM window of the RMU
display when operating in voice mode. The desired frequency should
be selected by the pilot using the RMU select knob. Communication
can be established pressing the third COM button on the audio panel
and the PTT button.
When in data mode, the third VHF transmits the data on the frequency
selected by the CMU unit, while on the RMU’s third COM window the
active frequency will display “DATA”.
The third VHF has a pilot-activated self-test that performs a check of
individual parts. A self-test is initiated when power is supplied to the
RMU.
The Avionics Master DC Bus 1A supplies the third VHF
Communications System.
THIRD VHF COM NORMAL OPERATION
In order to operate the third COM unit for voice communications, it is
necessary to properly set the RMU. By pressing the PGE bezel button
on the RMU, the page menu will be displayed. On the page menu the
“SYS SELECT” option should be chosen. Once selected, the System
Select page will be displayed containing the available COM pairs (1/2,
1/3 and 2/3), bandwidth of each COM unit and the COM3 operating
mode.
After selecting the COM pair to the corresponding RMU, the change
between each COM mode of the selected pair is achieved by pressing
the “1/2” bezel button.
The switch between data and voice modes can be accomplished by
means of the “SYS SELECT” page. The voice mode can also be
entered selecting the COM3 window and turning the RMU knob. The
data mode cannot be entered during a voice transmission. If a CMU is
installed and connected to the third VHF, it will enter the data mode
and “DATA” will be displayed in active frequency window when the third
VHF starts a data transmission.
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