Multiple Tasks on the Same Block

Certain additional simulation assumptions apply when multiple tasks (i.e., corrective, preventive, inspection and/or on condition tasks) apply to the same block:

• Downing events cannot overlap. For example, if a component is down due to preventive maintenance and a trigger suggests another preventive task, the suggestion is ignored.
• Non-downing events can overlap with downing events if they start at different times, provided that the non-downing event starts first. If the downing event starts first, then the non-downing event is ignored. If they start concurrently, the task with the highest priority will be performed.
• Preventive tasks and inspections cannot occur at exactly the time that the block or system comes up from another preventive task or inspection.

If multiple tasks are scheduled to occur at the same time for a block:

• If all are instantaneous (i.e., have a 0 duration), then all will occur.
• If any are non-instantaneous, then the tasks will be executed in order of priority, starting with the highest priority task, until one non-instantaneous task has been executed. In other words, only one non-instantaneous task will be executed, but all instantaneous tasks encountered prior to that in the priority list will be executed.

Tasks are prioritized as follows:

1. Tasks based on events in a maintenance group, where the triggering event applies to a block
2. Tasks based on system down
3. Tasks based on events in a maintenance group, where the triggering event applies to a subdiagram

If there is also a task based on interval scheduled to occur at the same time, the interval-based task OR the task highest in this priority list may be performed.

If a failure or preventive task occurs during a non-downing inspection, and the corrective task or the preventive task has a restoration factor, and the inspection task has a restoration factor, then both restoration factors are used (compounded).

If a corrective task is scheduled to be performed upon inspection and a preventive task occurs first, the preventive task will restore the block.

If a corrective task is scheduled to be performed upon inspection and a failure or preventive task occurs during a non-downing inspection, the restoration is compounded.