hi,i recenty noticed that i can switch off all fuel pumps in the 737-NG and the engines are still running. i can also start engines with fuel pumps off.how is that possible?regardsmalte

gravitation feedThe fuel pumps are NOT some sort of valves, they simply ensure the fuel flow in all certified situation. But you don't need em on the ground in reality. It's highly recommended you turn em on though.

thanks very much, didn't know that!

Actually, fuel is not gravity feed.When the Main tank AC fuel pump's are off, each engine can draw fuel from its corresponding main tank through a suction feed line that bypasses the pumps.As the airplanes climbs, dissolved air released from the fuel in the tank due to the decrease in airpreasure can collect in the suction feed lines and restrict fuel flow. At high altitude with main tank fuel pumps off, thrust deterioration or engine flameout may occur as a result of the fuel flow reduction.Floyd