Follo up Material - Stock

Hi,

We are using Follup Up Material opcion from MM02 MRP4, for example to change Material A to B

So we change to Bil of Material List.

When the Stock is zero, the mrp calculate new Planning Orders to material B.

But , if the material A have some Purchase Order Pending to Receipt, this situation isn´t considered.

When Material A, the stock is cero,MRP Grenerate a new orders to Material B without consider Purchese Orders of Material A

So the Production Orders, Generated use Material B insted of Material A .. but in the future may be we have stock of Material A (for receipt pending).

How to we guaranteeing that the Material A it being used up to final (stock and pending receptions)?

Regars