| ability to be in a state to perform as required under given conditions
Note 1 to entry: Availability considers two states, the up state (available) and the down state (unavailable). All time intervals, such as administrative delay (see Figure 1), are defined either as belonging to one of these two states or are excluded. (It is to be noted that the definition of Dependability does not refer to “states” as it has a much broader meaning. See 192-01-22 for further clarification).
Note 2 to entry: Availability depends upon the combined attributes of the reliability (192-01-24), maintainability (192-01-27), supportability (192-01-31) and the maintenance and support provided.
Note 3 to entry: Availability can also be affected by delays before any maintenance and support action is recognised. For example, delays due to fault detection time and administrative delay.
Note 4 to entry: Given conditions include aspects that affect availability, such as: mode of operation, stress levels (see 192-01-37 for examples), environmental conditions, and maintenance defined in the life profile.
Note 5 to entry: Availability may be quantified using measures defined in 192-08, Availability related measures.
NOTE 1: All times mentioned in the figure are time intervals or sequences of time intervals.
NOTE 2: Each time interval can be defined as required time (IEV 192-02-08) or as non-required time (IEV 192-02-09).
NOTE 3: In some cases, it may be possible to perform some maintenance when an item (IEV 192-01-01) remains functioning as required, see also on-line maintenance (IEV 192-06-30). To keep Figure 1 simple, the time associated with such maintenance is not addressed in the figure.
Figure 1 - Time intervals related to operation and maintenance
|