Forecasting for ERLA items?

Question

We are trying to enter sales forecast for our ERLA materials and then pass the demand down to the components.
Here is some background information:
      ERLA items are FERTs, but are not inventoried
      ERLA is the high-level item (kits) with material BOMs
      ERLA items are priced and invoiced in the sales order
      BOM components are inventoried and shipped to customers as unassembled kits
I tried to create a Product Group that mirrored the material BOM. Used Rough-cut planning to disaggregiate the demand down to the components. This works if the component only belongs to a single product group. If the component belongs to multiple product groups, the disaggregiation of the last product group overrode the earlier product group(s) data in the stock/requirements list. Our goal is to get the demand requirements down to the component level for production/procurement.
Is there another method of forecasting for these ERLA items and pass the components?
Is there some way to get the disaggregation to sum the demand at the component level, instead of overriding?

Answer 1

ERLA is item category group in material master, right?  FERT is your material type?  This is crucial since you can only run MRP for  quantity updating material (even though you will not have inventory for it).
I also assume the following: 
1. You have sales BOM that explode in sales order to issue the stock at unassemblied kits  ERLA served as the pricing.
2. You set the sales BOM to be able to used in MRP run as well.
This is a work around solution with some drawback.  Please try the following;  set the ERLA material with strategy planning w/o final assembly.  Maintain PIR at ERLA material.  System will explode the BOM and generate dependent requirement for unassembled kit.
Now if there is a sales order for ERLA material, sales order will consume PIR.  However, you will see double demand for sales order (assuming sales order BOM) for unassemblied kits and dependent requirement.  I recommend that you should not transfer the sales order requirement for unassemblied (setting at schedule line category in SD->Basic functions->Availability check ->transfer req -> define procedure for each scheduline line category).  This is to avoid double count of requirement for unassemblied kit.  You will need to run MRP at ERLA again to reflect the real demand of unassemblied kit (since sales order already consumed PIR).
The drawback is:
1. You will have convertible planned order at ERLA material for sales order.   You shouldn't do anything for this and make it firm then it will reflect the demand at the time you run MRP.  This is important since you need the planned order to pass the requirement to lower level.  You can't convert these to production order anyway since no routing is set up for ERLA.
2.  You need to run MRP at ERLA level to reflect the real demand for unassemblied kit.
I actually used this solution for one of my client.
Hope it helps.