How many signatures are required to release and revise aerospace engineering (drawings) and what documents, document sections drive this? Can a single person sign for a release or a revision? Can a single person sign in two places?
I have seen different things in different businesses and want to know what is minimum requirement and where the come from. For safety reason seems like two is the minimum (with the correct skills).
As an international standard that encompasses all of aerospace, AS9100 does not dictate any specific guidance on how signatures or approval of documents work. This is due to the fact that there could be very different customer of legal requirement around this topic depending on which part of aircraft, space or defense your organization works. For this reason, I cannot give you one right answer but rather you need to identify these requirements in your legal or customer requirements (the needs and expectations of interested parties identified in clause 4.2), and then incorporate these requirements into the QMS.
Much of what you have indicated, such as not having the same person write and review a document, are fairly common but not necessarily the rule for any particular company.