In engineering projects, it is common for critical components with long and unreliable delivery times to be purchased at an early stage in the project, well before the project activities, where these components will be consumed, are specified. Advance procurement is used to this end.
You can only use advance (preliminary) procurement if you are working with stock. This means that you must use item category L when assigning your components to ensure that stock can be managed. To offset the requirements for procurement against those of consumption, the components must be managed in the same (sales order or project) stock.
Planned Independent Requirements and Preliminary Purchase Requisition
The following list distinguishes between two scenarios: (1) Planned independent requirements, and (2) Preliminary purchase requisition.
Planned independent requirements: Assemblies that need to be produced well in advance of consumption are allocated as stock-items with the indicator planned independent requirement set for the procurement activity. The MRP run then generates a planned order, which triggers a production process. The production order will be delivered to stock where it will be consumed later by a second allocation to the consuming activity.
Preliminary purchase requisition: Assemblies that need to be ordered well in advance of consumption are allocated as stock-items with the indicator preliminary purchase requisition set for the procurement activity. The system then generates a preliminary purchase requisition, which triggers a purchasing process. The goods receipt for the component builds up stock. You can allocate the component to the consuming activity later, thus reserving and then consuming the stock.