Allen wrote:
"Mortimer Schnerd, RN" mschnerdatcarolina.rr.com wrote in message
...

On the C-402 for example, you had to burn a good 30 minutes on the
outboards (which were its mains) before you could switch to the inboards.
When you switched to the inboards, the fuel actually went from the
inboards to the outboards to the engine. If you didn't make room first by
burning the outboards first, the fuel pumped from the inboards would just
be pushed through the overflow valves on the outboard tanks and then you
get to sprinkle the landscape with expensive avgas.

You got that partially right. The aux tanks each have their own electric
fuel pump that pushes the fuel throught the selector valve and on to the
engine driven fuel pump. Excess fuel from the engine driven fuel pump is
routed back to the main (tip) tanks. The reason for running on the tip
tanks first for 60 (or 90 for the large aux tanks) minutes is to make room
for this bypass fuel.


Oops... it's been a while.



--
Mortimer Schnerd, RN
mschnerdatcarolina.rr.com