You guys think way too complicated.

 

On the contrary.

It depends whether you are more challenged by the space or time visualization dimension.

Anyway, you didn't answer the question as posed.   Surely you can think of a failure

mode other than operator error.

Yep!

 

Every tank that feeds an engine directly must have a carefully constructed slosh chamber to ensure there is no unporting of the fuel during some uncoordinated maneuver (maybe any maneuver, but especially climb and descent**).  Usually such tanks cannot be fully utilized - i.e. sizable amounts of unusable fuel.  An aux tank with a pump only needs baffles to keep large amounts of fuel from sloshing about and, in level flight, can be completely emptied if so constructed.  

 

I have a small airplane but I can (and have) completely drained the wings into the 9 gal header. The header is the sole supplier of fuel to the engine and is kept within one gallon of being full until the wings are empty.  Should I have a complete failure of most everything electrical, I have about 1.25 hours (or more, reduced power, LOP) to find an airport. The header provides a head to the fuel to assist a pump find fuel should it cavitate from having the vapors. Out of the 43 gallons I can carry, I can use 42.4.  I have no selector valve, hence no selection election error.  Both wings are emptied in unison, thus no lateral trim imbalance during cruise.  If any part doesn't work, I land.  I don't contemplate flights over the Big Pond.

 

I am not suggesting you consider a header tank - there are some that are nervous about it becoming an anti-fungal foot bath.  For airplanes with two wings but more than two tanks, I would transfer pump the aux tank(s) to the wing(s), thus a simpler system that makes more fuel usable.

 

To each his own.  Results may vary.