Association
2- The plot-to-track association is the process of relating incoming surveillance sensor data to an already existing ARTAS track in a one to one relation
ATC Complexity Categories (En-Route & TMA)
A classification of Area and Approach Control Centres based on criteria that include:
-air traffic vollume (during a peak period)
-
traffic density (relation between traffic and airspace volume)

-
traffic complexity (eg.: route network, density, proximity of large airports)

This classification - which is no longer in use in EATM - was suggested in the ECAC En-Route Strategy for the 1990s (now superseded by the EUROCONTROL ATM 2000+ Strategy) to recognise that ATC systems should be tailored to cater for different levels of complexity and be adapted to the particuliar requirements and development possibilities of different air traffic density areas.
ATCO margin
The difference between the number of ATCOs required and ATCOs available.
Attenuation
1- The reduction of a correlation or regression coefficient from its theoretical true value due to the imperfect reliability of one or both measures entering into the relationship (CDSEPT, 1996).
2- Reduction in the strength or quality of a signal because of an intervening medium
Attitude
A mental position or feeling with regard to some matter.
Attitude Display Indicator
The ADI is the nucleus of primary flight instruments, providing pilots with both aircraft pitch and roll information along the longitudinal and lateral axis of rotation. Most modern ADIs are equipped with a flight director and mode enunciator which is integrated with the Auto Flight Control System. Navigation data is routed to the ADI's flight director, from either independent VOR, NDB, INS and/or GPS receivers or through a flight management system to provide pilots or the Auto Pilot with the appropriate lateral and vertical guidance.
Attitude Heading Reference System
The Attitude Heading Reference System provides attitude gyro, directional gyro (compass) and 3-axis rate/accelerometer data to the following aeroplane systems in EFIS equipped aircraft : Primary flight and multi-function displays; Weather radar system; Automatic Flight Control System; Ground Proximity Warning System; Traffic Alert and Collision Avoidance System; Stall Protection System; Fuel System; Flight Data Recorder; Body Rates and Linear Acceleration Data to the flight control system.
Audio Aids
Aids to communication which utilise the sense of hearing.
Audio-Visual Aids
The generation, recording, storage and reproduction of animated images and associated sounds (video, films and other).
Augmentation (GNSS)
GNSS augmentation is a technique of providing the system with input information, extra to that derived from the main constellation(s) in use, which provides additional range/pseudo-range inputs or corrections to, or enhancements of, existing pseudo-range inputs. This enables the system to provide a performance which is enhanced relative to that possible with the basic satellite information only.