My Captain at the time and I had problems with a ferry fuel system in a Twin Otter. With his experience and wisdom, he resolved it, while I simply flew (this was not a one pilot problem). I also required lung power to fix the problem.
This crew:
https://www.baaa-acro.com/city/honolulu?page=1
Was not so lucky.
When I approve ferry fuel systems, I'm looking for all the possible failure modes, as there is much less frequently a plan B!