| time interval for which the item is in a down state
NOTE 1 All times mentioned in the figure are time intervals or sequences of time intervals.
NOTE 2 In the bottom row, RT signifies required time and NRT signifies non-required time, although these are not normative abbreviated terms.
NOTE 3 In some cases, it can be possible to perform some maintenance when an item remains functioning as required; see also on-line maintenance. To keep Figure 1 simple, the time associated with such maintenance is not addressed in the figure.
Figure 1 – Times related to operation and maintenance
Note 1 to entry: Down time excludes disabled time due to lack of external resources, but includes maintenance time less any on-line maintenance time.
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