Active Reflector A device used in Primary Radar systems for geo-graphical alignment and system performance checking: It generates a signal from a stationary installation with an artificial Doppler shift which en-sures that a stationary target will be presented on an ATC screen after Moving Target Detection (MTD) or Moving Target Indicator (MTI) processing. Active Way-Point A way-point to or from which navigational guidance is being provided. For a parallel offset, the active way-point may or may not be at the same geo-graphical position as the parent way.point. When not in the Parallel offset mode (operating on the parent route), the active and Parent way-points are at the same geographical position. Activity An element of work performed during the course of a programme / project or within the scope of a service. Actual implementation date Date by which a Convergence and Implementation Programme Objective has been achieved. Actual Time of Arrival Filled in on arrival. Also used for ATO. Actual Time Over Filled in when an aircraft passes (flies over) a co-ordination point (e.g. a beacon). ADA A higher-order programming language for use in embedded real-time avionics computers. (ANSI / MIL/STD/1815). Added function See Advanced Functionality Tool Address Domain An (ATN) Address Domain is a set of address for-mats and values administered by a single address authority. Under the ISO plan, any address authority may define sub-domains within its own domain, and delegate authority within those sub-domains. Addressing Authority An (ATN) Addressing Authority defines formats and/or values of NSAP addresses within its jurisdiction. Adequate Warning Time The desired warning time for particular alerts given by a particular Safety Net in a particular region (SNET) type. The value is determined externally, based on human factors and aircraft performance considerations. Adjacent Track Track provided to an ARTAS Unit by one of its adja-cent Units. Adjacent Unit Two ARTAS Units are adjacent if a Domain of Co-operation is defined between them. Administrative Domain A collection of (ATN) end systems, intermediate systems and sub networks operated by a single or-ganisation or administrative authority. An adminis-trative domain may be internally divided into one or more routing domains. Adopted airports (AMAN) Airports especially defined being considered within the AMAN operational horizon.