(2)
ARTS IIA -A programmable radar-tracking computer subsystem capable of modular expansion. The ARTS IIA detects, tracks, and predicts secondary radar targets. The targets are displayed by the means of computer-generated symbols, ground speed and flight plan data. Although it does not track primary radar targets, they are displayed coincident with the secondary radar as well as the symbols and alpha numerics. The system has the capability of communicating with Air Route Traffic Control Centers and other ARTS II, IIA, III, and IIIA facilities.

(3)
ARTS III - The Beacon Tracking Level (BTL) of the modular programmable automated radar terminal system in use at medium to high activity terminals. ARTS III detects, tracks and predicts secondary radar derived aircraft targets. These are displayed by means of computer generated symbols and alpha numeric characters depicting flight identification, aircraft altitude, ground speed and flight plan data. Although it does not track primary targets, they are displayed coincident with the secondary radar as well as the symbols and alpha numerics. The system has the capability of communicating with Air Route Traffic Control Centers and other ARTS III facilities.

(4)
ARTS IIIA - The Radar Tracking and Beacon Tracking Level (RT&BTL) of the modular, programmable Automated Radar

Terminal System. ARTS IIIA detects, tracks, and predicts primary as well as secondary radar derived aircraft targets. This more sophisticated computer-driven system upgrades the existing ARTS III systems by providing improved tracking, continuous data recording and fail-safe capabilities.
AUTOMATED SURFACE OBSERVATION SYSTEM/ASOS (NGA) - The primary surface weather observing system of the United States. It provides continuous minute-by-minute observations and performs the basic observing functions necessary to generate a Surface Aviation Observation (SAO) and other aviation weather information.
AUTOMATED WEATHER OBSERVATION SYSTEM / AWOS (NGA)
- A real time weather observation system used to broadcast local minute-to-minute weather data directly to aircraft.
AUTOMATIC ALTITUDE REPORTING - That function of a transponder which responds to Mode C interrogations by transmitting the aircraft's altitude in 100-foot increments.
AUTOMATIC CARRIER LANDING SYSTEM/ACLS - United States Navy final approach equipment consisting of precision tracking radar coupled to a computer data link to provide continuous information to the aircraft, monitoring capability to the pilot and a backup approach system.