User Guide

Series III Avionics
Pilot's Guide
Page 42
DMS-44A Notes
1. DME operates within a band of 252 internationally assigned frequency channels from 962 Megahertz
to 1213 Megahertz. All channels are not currently in use, but the DMS-44A is tunable to all 252.
2. DME equipment aboard the aircraft measures the delay between interrogation pulses transmitted and
reply responses received. This delay is converted to distance, and, as distance changes with time, to
ground speed. The distance is "slant range," not horizontal, over-the-ground distance.
3. If a single DMS-44A System is installed with two SD-442B Selector Displays, NAV System 1 may be
selected on one display and NAV System 2 on the other. Each NAV System may then select
separate DME stations.
4. When RNV is selected, the displayed distance is horizontal, not slant, range, distance to the
waypoint. Also, no DME station identification will be present.
5. When turned on, the DMS-44A will remember and display the last mode(s) used, and will be tuned to
the last channels selected before power was removed. On the ground, the display will probably be
flagged because of signal distortions.
6. Because of assigned "pairing" of VHF and MLS navigation facility frequencies with DME channels,
airborne DME equipment is designed to be tuned to the correct DME channel/ frequencies
automatically when a VHF navigation frequency or MLS channel is selected by the pilot. It is not
necessary to know actual DME channel and frequency assignments.
7. When the DMS-44A transmits its interrogation pulses and receives invalid responses or none, the
SD-422 Selector Display indicates this condition by flagging the display with dashes. This is a normal
condition when the ground DME station is out of range, the reply pulses are too weak or unreliable to
process, the ground DME station is out of service, or there is no DME station assigned to the VHF
navigation facility to which the NAV Receiver is tuned.