Way-point Displacement Area The rectangular area formed around the plotted position of the waypoint. The rectangle is oriented along the desired track with the waypoint at its centre. Its dimensions are two times the appropriate plus-or-minus along-track and cross-track displacement error values. W-Code Encryption Code to encrypt the P-code into the Y-Code. Weather Office A generic external entity providing the FDPS with meteorological information. What-if-probing (AMAN) An optional AMAN feature that allows the controller to test different control solutions before taking a decision. What-if-probing usually involves utilisation of a tentative trajectory (very advanced AMAN only). Wide Area Augmentation A wide area augmentation is defined as providing additional satellite signals over a wide area in order to enhance the integrity and/or availability and/or accuracy of the GNSS services. Wide Area Augmentation System A service being developed by the FAA to provide wide area DGPS and integrity information to aviation users. Wide Area Differential GNSS A real-time DGNSS system that is made available over a large area - possibly global. Wide Area Differential GPS A real-time DGPS system that is made available over a large area - possibly global. Wide Area Network Wide Area Networks are used to interconnect geographically dispersed routers and host computers. These sub networks may be internally complex packet switching entitles of their own, or they may be as simple as point-to-point dedicated lines. Wide Area GPS Enhancement programme WAGE provides Equivalent Range Deviations (ERDs) to authorised users through sub frame 4 of the GPS navigation message. Wider System The area defined within the overall environment that provides resources to, and legitimises the operations of, each of the systems operating within it. It also formulates the initial design of the systems operating with it and makes known its expectations of each system operating within it. Window A restriction in real space (and/or time). Work Breakdown Structure A deliverable-oriented grouping of project elements which organises and defines the total scope of the project. Each descending level represents an increasingly detailed definition of a project component. Project components may be products or services. Work Package A deliverable at the lowest level of the work breakdown structure. A work package may be divided into activities.

Working Memory
Also known as short-term memory, working memory stores information currently being used or attended to. It has as a capacity of between five to nine ‘chunks’ of data at any one time, and data not attended to is lost within about 30 seconds. Skilled representations and mental models are active in working memory when used to support task performance.
Working Practices
Customs and practices developed to ensure a consistent approach to the structuring of work in the various operational functions at ATS units.
Working Time
Any period during which the workers are working, at the employer’s disposal and carrying out their duties, in accordance with national laws and / or practice (after CD, 1993).