DIR  Director 
Directed  A DME operating mode that allows an FMCS to select 
Mode  one to five DME stations for interrogation. 
DISCH  Discharge 
DITS  Data Information Transfer System 
DL  Data Link 
DLC  Data Link Control Display Unit 
DLGF  Data Load Gateway Function 
DLM  Data Link Management Unit 
DLODS  Duct Leak and Overheat Detection 
DLP  Data Link Processor 
DLS  Data Load System 
DLU  Download Unit 
DMA  Direct Memory Access 
DME  Distance Measuring Equipment. A system that pro-
vides distance information from a ground station to 
an aircraft. 
DME/N  Abbreviation for a DME normal system. 
DME/P  Abbreviation for a DME precision system. 
DMM  (1) Digital Multimeter 
(2) Data Memory Module 
DMS  Debris Monitoring Sensor 
DMU  Data Management Unit 
DOC  Documentation 
DOD  Department of Defense 
DOP  Dilution of Precision 
Doppler  The change in frequency observed at the receiver 
Effect  when the transmitter and receiver are in motion rela 
tive to each other. 
DOT  Department of Transportation 

DOTS  Dynamic Ocean Tracking System 
Downlink  The radio transmission path downward from the air-
craft to the earth. 
DPR  Dual Port RAM 
DPSK  Differential Phase Shift Keying 
DRER  Designated Radio Engineering Representative (FAA) 
Drift Angle  The angle between heading and track. It is due to the 
effect of wind currents. Sometimes called the crab 
angle. 
DRMS  Distance Root Mean Square 
DRN  Document Release Notice 
DSARC  Defense System Acquisition Review Cycle 
DSB  Double Side Band. An AM signal with the carrier 
removed. Requires the same bandwidth as the AM