Recently went through audit to recertify to ISO 9001:2008/AS9100 Rev B. We struggle with writing effective root cause statements. Our first nonconformance was for NOT having an established system for flowing down customer requirements to purchasing and then on to supplier. We are a very small company and this information has always been communicated by email as well as noted on our production schedules. We thought the root cause of our NCR was that neither the customer service nor purchasing procedure gave guidelines on HOW to flow down the information. We stated that and we added purchasing to our work traveler and we added this step to our procedures. Our auditor told us that our root cause statements for all our NCRs were 'weak' and unacceptable. Auditor asked "WHY wasn't this information on our procedures." I am seriously at a loss for the next step in the WHY process. We have struggled with root cause statements for almost 4 years of ISO/AS certification. Why don't the registrars 'train' us in this mindset?