probability for an item to be in a state to perform as required at a given instant
Note 1 to entry: In this Technical Report the word “availability” used alone stands for “instantaneous availability”.
Note 2 to entry: This is a time-dependent parameter.
Note 3 to entry: No matter if the item has failed before the given instant if it has been repaired before.
Note 4 to entry: For non-repairable items, Availability and Reliability are identical.
Note 5 to entry: When dealing with safety, A(t) is generally close to 1 and this property is used to develop
approximated formulae (see Clause 7).
Source: ISO/TR 12489:2013(E) Reliability modelling and calculation of safety systems. Global Standards