Spare Part Pools - Simulation Assumptions

The underlying simulation assumptions for spare parts are:

• Spare parts are always required for corrective and preventive tasks.
• If a spare part pool has not been assigned to the task, then it is assumed that unlimited free spares are always available.
• Spare parts are never required for inspection tasks.
• Once a part is ordered from a spare part pool, it is considered to be dispensed by that pool, even if it was ordered and has not yet arrived by the end of the simulation (much the same way the block is charged for it, even if it does not arrive).
• If the spare parts pool cannot provide enough parts to a task (including restocks), the task will remain in "Waiting for spare parts" status to the end of the simulation.
• All restocking that occurs during simulation is based on the settings of the spare part pools.
• If the Restock as needed check box is selected, a restock will be triggered every time a task requests parts from the pool, if that request causes the number of items in the pool to drop below the limit specified in the Restock when stock drops to field.
• If the Can obtain emergency spares if needed check box is selected, an emergency restock will occur only once for each execution of a task, if there are insufficient parts in the pool to cover the request.
• If the Scheduled Restock and Restock as needed check boxes are selected, then if a spare part from a scheduled restock can arrive before a spare part from an on condition restock, the spare part from the on condition restock will be ordered but will not be used in the maintenance task.
• A block that triggers an emergency restock is charged for the additional emergency cost, even if it did not use the restock part(s) (e.g., another part became available from a scheduled restock first).
• The average stock level (ASL) metric in the simulation results is based on how many times the stock level was determined (e.g., every time a request is made, whether it is rejected or accepted, etc.). The average stock level is recorded at the beginning and at the end of each simulation.
• Off-site spare parts are ordered regardless of whether they will arrive before the simulation end time. This means:
  • When a block orders a spare part from an off-site pool, the part is ordered (and the block is charged for it) without regard to arrival time.
  • Off-site emergency spare parts will be ordered by both on-site and off-site pools without regard to arrival time.
  • On condition restock from off-site pools will be performed without regard to arrival time.