Note 1 to entry: Availability depends upon the combined characteristics of the reliability (192-01-24), recoverability (192-01-25), and maintainability (192-01-27) of the item, and the maintenance support performance (192-01-29).

Note 2 to entry: Availability may be quantified using measures defined in Section 192-08, Availability related measures.

time interval

up time

down time

enabled time

externally disabled time

enabled time

down time

operating time

non-operating time

operating time

non-operating time

idle time

standby time

externally disabled time

preventive maintenance time

time to restoration

corrective maintenance time

fault detection time

administrative delay

maintenance time (see Figure 2)

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