AIRCOM  Digital air/ground communications services provided 
by SITA. A system similar to ACARS. 
AIR DATA  Those parameters that can be derived from knowl-
edge of the air mass surrounding the aircraft. 
Airways  The standard ICAO IFR routes 
AIS  Aeronautical Information Services 
AISC  Aeronautical Industry Service Communication 
AIV  Accumulator Isolation Valve 
A/L  Autoland 
ALC  Automatic Level Control. A circuit used to maintain 
the output of a transmitter regardless of variations in 
the attenuation of the system. 
ALS  Advanced Landing System 
ALT  (1) Airborne Link Terminal 
(2) Altitude 
Altitude  A continuous return across the display at a range 
Ring  equivalent to aircraft altitude (WXR). 
ALTS  Altitude Select 
ALU  Arithmetic and Logic Unit 
AM  Amplitude Modulation. A signal where the carrier sig-
nal is varied in amplitude to encode voice or data 
information. 
AMASS  Airport Movement Area Safety System 
AMC  Avionics Maintenance Conference 
AMCP  Aeronautical Mobile Communications Panel 
AME  Amplitude Modulation Equivalent. An AM type signal 
that processes the modulated information signal and 
carrier frequency separately and then reconstructs 
the two signals to make an equivalent AM signal. 
AMI  Airline Modifiable Information 
AMLCD  Active Matrix Liquid Crystal Display 
AMOSS  Airline Maintenance and Operations Support System 

AMP  Audio Management Panel 
AMPL  Amplifier 
AMS  Apron Management Service 
AMS(R)S  Aeronautical Mobile Satellite (Route) Service 
AMSS  (1) Aeronautical Mobile Satellite Service 
(2) Aeronautical Mobile Satellite System 
AMTOSS  Aircraft Maintenance Task Oriented Support System. 
An automated data retrieval system. 
AMU  Audio Management Unit 
AMUX  Audio Multiplexer 
A/N  Alphanumeric 
Aneroid  An evacuated and sealed capsule or bellows which