The AS9100 Rev D standard does not specify how you identify root cause analysis, so unless you have customer requirements telling you how you will do the root cause analysis you can choose any way you wish; 5 Why, fishbone, 8D, etc.
It is also useful to note that the new revision of AS9100 now allows you to made a determination for your process nonconformities to determine if you require the full root cause analysis and corrective action to address this (See clause 10.2.1 b). You do need to correct the problem and deal with the consequences, but you can then determine if you need to take action to eliminate the cause of the nonconformity. Again, if your customer is requiring you to perform full root cause analysis on a problem you will not have a choice.
For more information on the corrective action process in AS9100 Rev D see this article: https://advisera.com/9100academy/knowledgebase/corrective-actions-vs-continual-improvement-in-as9100/