Service
1- An abstract noun which is used to designate functions, or a service rendered. It refers to a set of actions, both systems supported and manual, which have a clearly defined operational goal and which begin and end on an operational event.
2- An ARTAS Track Information Service is characterised by: the Track Selection the Item Selection (i.e. the composition of the track messages to be served); the Transmission Characteristics (i.e. the required type of data transmission). An Elementary Service is defined as a combination of one Track Selection and one Item Selection associated with one set of Transmission Characteristics. A Combined service is defined as a combination of several elementary services, so-called Background and Complementary services. The Background service defines the minimum service to be provided under all circumstances.
Service Access Point Conceptual point at which a service user accesses the service provider in a layered communication system associated with an address. Service Coverage The coverage provided by a radio-navigation system in that area of space volume in which the signals are adequate to permit the navigator to determine position to a specific level of accuracy. Coverage is influenced by system geometry, signal power levels, receiver sensitivity, atmospheric noise conditions and other factors which affect signal availability. Service Data Unit A unit of data transferred between adjacent layer entities which are encapsulated within a PDU for transfer to a peer layer. Service Manager Accountable for meeting the agreed service level within budget: Defines and gets agreement to the service level to be provided; Reports regularly to the Line Manager; Manages and develops the service team; Manages allocated resources to achieve agreed service level; Liaises with the customer. (EATMP Management Roles and Responsibilities). Session Layer The layer of the OSI reference model that establishes the rules of dialogue between two end-user entities. Session Service Selector The element of the session address that identifies the user of the session protocol entity. Sextant A double-reflecting instrument for measuring angles, primarily altitudes of celestial bodies. Shadowing Passive supervised practice on real equipment which is in operation. Shall, Should, Will, May 1- Shall : denotes a mandatory requirement;
2- Should : denotes a preferred requirement;
3- Will : denotes a statement of interest;
4- May: denotes an option. Shift The time of day on a given day that an individual or a group of individuals are scheduled to be at the workplace. (Tepas and Monk, 1987).

 
Shift Break Time within a shift when work is not required, usually a time period of less than 1 hour in duration. This includes lunch breaks, rest breaks, relief breaks, and all other forms of workplace release from work (Tepas an Monk, 1987). Shift Roster / Shift Schedule The sequence of consecutive shifts and off time assigned to a particular individual or group of individuals as their usual work schedule. Short Route Flight A flight operating within the AMAN operational horizon. Short-Term Sensory Store The short-term sensory store is related to the perception of information in the different receptor systems. Side Lobe Suppression A mechanism in an SSR transponder activated by the transmission (radiation) of a Control Pulse (P2 or P5) of amplitude greater than the antenna side lobe signals in space, which will enable the transponder to prevent itself from replying to the side lobe interrogation signals.