I just flew a short flight from Pheonix to Salt Lake City in a -900 and although I had the fuel tank selection on the center tank; it was feeding off the wing tanks. I even shut off the aft fuel pumps to see if this would force feed off the center tank but it did not. Why is that sometimes flights will feed off the center and other times off the wing tanks. Also, once you shutdown, and restart for another leg the a/t won't work. If you try engauging the a/t first light will flash. Help please.

>I just flew a short flight from Pheonix to Salt Lake City in>a -900 and although I had the fuel tank selection on the>center tank; it was feeding off the wing tanks. I even shut>off the aft fuel pumps to see if this would force feed off the>center tank but it did not. Why is that sometimes flights will>feed off the center and other times off the wing tanks. Also,>once you shutdown, and restart for another leg the a/t won't>work. If you try engauging the a/t first light will flash.>Help please.First things first; make sure that you have the main engine driven generaters online. The autothrottle "flash" you see is an indication that you are still on the APU driven gen and not the main engine driven gens. (NOTE: FOLLOW THE CHECKLIST!)For the fuel pumps; if you need to feed from the center tanks, turn on ALL fuel pumps. when the center tank empties, turn off the center tanks (i.e. The wing tank pumps should never be turned off!) See if that fixes your tank-feed issue.