User Guide

Series III Avionics
Pilot's Guide
Page 39
DMS-44A Controls
The DMS-44A has only three controls, all located on
the SD-442B Selector-Display Unit. Each is a
momentary, spring-loaded type that releases when
finger pressure is removed. On-off power is through
an external switch such as a radio or avionics
master switch, or a dedicated DME switch. Volume
control of DME station identification audio is also
external, typically located on an audio panel.
NAV - Alternately places annunciator 1, 2, or RNV
in display.
1 - Selects NAV System 1 as the controller of
the DME channel.
2 - Selects NAV System 2 as the controller of
the DME channel.
RNV - Allows the SD-442B Selector Display to
be used as a "repeater" display or
RNAV-computed distance to a waypoint
and ground speed. This allows RNAV
data to be available during times it might
not be displayed by the RNAV System (for
example, when other data is selected for
display on some types of RNAV's).
HOLD
- Pressing and releasing this switch does the
following:
A. Locks the appropriate channel of the
DMS-44A to the current DME frequency in
use. Aircraft wiring will effect the way in
which the hold feature works. In some
installations, pin 58 ground, the hold switch
will only place the corresponding channel in
hold. In others, pin 58 open, the hold switch
will place the displayed channel into hold.
B. Displays the current NAV frequency that
determines the DME channel.
C. Disconnects control of the DMS-44A from the
NAV Receiver.
D. Displays annunciation HLD.
The purpose of this switch is to allow the
NAV Receiver to be set to other frequencies
without affecting DME operations. The DME
continues to function on its "holding" channel.
Pressing and releasing this switch while in
the HLD mode will return control back to the
indicated NAV System (1 or 2).