ADI  Attitude Direction Indicator 
ADIRS  Air Data Inertial Reference System 
ADIRU  Air Data Inertial Reference Unit 
ADLP  Aircraft Data Link Processor 
ADM  Air Data Module 
ADMS  Airline Data Management System 
ADP  Air Driven Pump 
ADRAS  Airplane Data Recovery and Analysis System 
ADS  (1) Automatic Dependent Surveillance 
(2) Air Data System 
ADSB  Automatic Dependent Surveillance – Broadcast 
ADSEL  Address Selective. A SSR system electronic-ally 
arranged to address each transponder selectively. 
Only a particular transponder will respond,thus 
avoiding garbling. ADSEL uses a monopulse tech-
nique to provide more accurate bearing measure-
ment. ADSEL is compatible with DABS. (Refer to 
Mode S transponders.) 
ADSP  Automatic Dependent Surveillance Panel 
ADSU  (1) Automatic Dependent Surveillance Unit 
(2) Automatic Dependent Surveillance System 
AECU  Audio Electronic Control Unit 
AED  Algol Extended for Design 
AEEC  Airlines Electronic Engineering Committee 
AEP  Audio Entertainment Player 
AERA  Automated En Route traffic control 
AES  Aircraft Earth Station 
AFC  (1) Automatic Frequency Compensation 
(2) Automatic Frequency Control 
AFCAS  Automatic Flight Control Augmentation System 
AFCEA  Armed Forces Communications & Electronics 
Association 

AFCS  Automatic Flight Control System 
AFD  Adaptive Flight Display 
AFDC  Autopilot Flight Director Computer 
AFDS  Autopilot Flight Director System 
AFEPS  ACARS Front End Processing System 
AFIS  (1) Automatic Flight Information Service 
(2) Airborne Flight Information System 
AFS  Aeronautical Fixed Service 
AFSK  Audio Frequency Shift Keying 
A/G  Air-Ground 
AGACS  Automatic Ground-Air Communication System (also 
known as ATCSS,or DATA LINK) 
AGARS  Advanced General Aviation Research Simulator 
AGC  Automatic Gain Control. AGC is used to maintain the 
output level of the receiver. 
AGL  Above Ground Level 
AGS  Air/Ground System 
AHOE  Air/Oil Heat Exchanger 
AHRS  Attitude Heading Reference System 
AI  Alternative Interrogator 
AID  Altered Item Drawing. A drawing that details what