Agreed with Pilchard and Three Bouyyy.In fact, this question includes the risk assessment and management and contingency planning of suppliers. especially the critical suppliers, it will affect delivering a product to the customer on time if the critical supplier stops and supply the material. so you need to do a risk assessment and management as well as contingency planning for the critical suppliers. the written investigation, on-site capability evaluation, sample testing, and small lot trial may be carried out by us to the critical supplier. whereas, we only may need to written investigation and on-site capability evaluation. We may need to quality inspection certificate for the critical suppliers, instead, no need for non-critical suppliers. In the sample planning of incoming material, the AQL values should be small a little for critical suppliers, but the AQL values should be big a little for non-critical suppliers and so on. so we should classification and control our suppliers according to critical suppliers and noncritical suppliers.