Originally Posted by jannis
Can I refuse to get involved if I am the only MD or health professional onboard?
Your own professional and ethical standards are the same wherever you might be in the world, regardless of jurisdiction. If they are at all similar to mine, then these would ensure that you always become involved, to a level consistent with your experience. (Possible exception, if too much ethanol consumed?)
On a similar note, I don't think being on an aircraft is ever a good enough reason for me to take decisions that I am not adequately qualified to take elsewhere. This would include the decision to divert -- surely the captain has the final call, once he has enough information about the degree of urgency.