hi on a recent flight my 737-900NG was running out of fuel on the central tank, but i noticed that the wings were 100% full, i turned on the switch for crossfeed fuel but nothing happenened can someone explain me how to crossfeed fuel to the central tank?

The engines are feed from the wing tanks (see the AOM - Aircraft Operating Manual). All you have to do when the center tank is empty is turn off the pumps; real world they leave a couple of thousand pounds in there to keep the pump submerged, I think.The only time you ever need crossfed is to balance the wing tanks, such as when operating single engine.Be sure to refer to the AOM.

thanx that is for great help to me :)

When there is fuel in the center tank and the pumps are on the fuel comes directly from the center tanks. The center tank pumps operate at a higer pressure than the wing tanks so eventhough all the pumps are on fuel only flow to engines from the center tank. Once the center tank is empty the pumps get low pressure and the wing tanks then start to feed fuel to their respective engines. Center fuel is burned first during all normal operations. There is a limitation that if there is more than 1000 pounds of fuel in the center tank that the wing tanks must be full. Fuel can not be transferred from tank to tank with the crossfeed. All the crossfeed valve does is allow fuel from one side to go to the engine on the opposite side.The procedure we use now for center tank fuel is when it gets to 2000 pouond we open the crosfeed and turn off one pump. That way the remaining pump can send fuel to each engine. Once the low pressure light comes on the master caution will come on and the center pump is turned off and crossfeed closed. With two center tank pumps on the master caution will not come on when only one pump has low pressure.