This standard defines a risk-performance based methodology for the surveillance of Design Suppliers compliant with EASA Part 21.A.239 (a) (3) and 21.A.239(c)@ and equivalent military DOA requirements (EMAR 21). That methodology is applicable to any level of Design Supplier??s (Sub Tier n) position in the supply chain of a DOA Holder. NOTE For convenience in this document the Tier n (who can be DOA holder itself or one of the Tier n below) is called ??purchaser?? when monitoring the subsequent design supplier (sub Tier n+1). It is assumed in this standard that the purchaser since DOA holder has already an Independent System Monitoring in place and effective