Quite some long time ago I seem to recall a case of an aircraft accident in UK where both pilots on board were held to blame by the CAA. One of the pilots claimed that he could not be held liable because he wasn't a designated member of the crew. The CAA disagreed, stating that if you're sitting in a crew seat and qualified to fly the type you're part of the crew. Unfortunately I cannot recall when or where this was, but the thought has always stuck with me since.