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tifier legend are backlit with electrolumines-
cent lighting.
The CDH controls (Figure 16-18) are as follows:
• Transfer Key – Alternately selects either
the COM (top) or NAV (bottom) fre-
quency to be connected to the tuning
knobs.
• Tuning Knobs – Used to change the fre-
quency indicated by the tuning cursor.
• Normal/Emergency Mode Switch – This
rotary knob provides alternate selection
of Normal and Emergency modes (See
Emergency Mode annunciation, below).
• NAV Audio On/Off Switch – This switch
is used to toggle NAV audio ON or OFF
when in the EMER audio mode on the
audio control panel. In this mode, COMM
1 and NAV 1 audio levels default to a
preset level. The pilot will want to re-
ceive COMM 1, but will not usually want
to monitor NAV 1 audio continuously.
• Squelch (SQ) Switch – Used to toggle
COM squelch On or Off.
• NAV Audio On Annunciator – Indicates
when NAV audio has been selected on.
The CDH annunciations are as follows (Figure
16-18):
• System Installation Annunciator – The
number 1 in the upper left corner of the
display indicates the CDU can only be
used to control COM1 and NAV1.
• Tuning Cursor – The tuning cursor an-
nunciator is a lighted triangle which is
controlled by the transfer key. It indi-
cates which frequency can be changed
by the tuning knobs.
• Transmit (TX) Annunciator – Indicates
when the COM transmitter is on.
• Emergency Mode Annunciator – Indicates
when the CDH has been placed in the
emergency mode. In the normal mode
there is no annunciation. In the emer-
gency mode, COM1 and NAV1 are tuned
exclusively by the CDH. This annuncia-
tor is not related to the emergency COM
frequency of 121.5, nor to the EMER se-
lection on the audio control panel.
The CDH has two modes of operation, normal
and emergency. In the normal mode, the CDH
acts as a tuning source in addition to the two
RMUs and/or FMS. The displays always show
the frequencies to which the radios are tuned.
This information is obtained via the radio sys-
tem bus. Tuning a radio is accomplished by se-
lecting the appropriate unit (COM or NAV)
with the transfer key, and then turning the tun-
ing knobs until the desired frequency is set.
The data is sent to the COM or NAV unit via
an auxiliary bus and the CDH verifies that the
radio has accepted the tuning command by
listening to the echoed frequency on the radio
system bus.
In the emergency mode, RMU and FMS tun-
ing capabilities are inhibited and the COM and
NAV units are tuned exclusively by the CDH.
An “AUX ON”message is displayed at the top
of the COM 1 and NAV 1 windows of the #1
RMU to indicate that tuning through the RMUs
is inhibited. Tuning through the CDH is no
different when EMRG is selected, but the CDH
does not look at the radio bus data to check the
echoed frequency
L E A R J E T 4 5
P I L O T T R A I N I N G M A N U A L
16-27
FOR TRAINING PURPOSES ONLY
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