non return valves
If either of the non return valves on the transfer pumps is jammed in the closed position,
are there any flight deck warnings? Pitch change will have interesting results.
Having studied the diagram of the fuel system left me with an uncomfortable feeling.
I have fixed wing experience only. 16000 hours on many types, some with good fuel systems and a few which gave me concern. The one thing that always stops any engine is lack of fuel.