Active Maintenance Time
That part of the maintenance time during which a maintenance action is performed on an item, either automatically or manually, excluding logistic delays. NOTE 1 A maintenance action can be carried out while the item is performing a required function. NOTE 2 For a more detailed description and interpretation of maintenance times, see Figure 4 and Annex C.
Source: API STD 2000, Venting Atmospheric and Low-pressure Storage Tanks, Sixth Edition, November 2009. Global Standards