This is just a curiosity question:I've always wondered why on the 737NG (any model) overhead panel as implemented, indicator warning lights for the center fuel tanks are always off regardless of the state of their respective pump switches.Those for left and right tanks come on when their pumps are off.Perplexedly yours,

>This is just a curiosity question:>>I've always wondered why on the 737NG (any model) overhead>panel as implemented, indicator warning lights for the center>fuel tanks are always off regardless of the state of their>respective pump switches.>>Those for left and right tanks come on when their pumps are>off.>>Perplexedly yours,>>>>>>>Because.....Center Tank Fuel Pump Low Pressure Lights - Illuminated amber if fuel output is low and Fuel Pump switch is ON.- Extinguished if fuel pump output pressure is normal, or Fuel Pump switch is OFF.Main Tank Fuel Pump Low Pressure Lights-Illuminated amber if fuel pump output pressure is low, or Fuel Pump switch is OFF.-Extinguished if fuel pump output pressure is normal.Make sense now?Floyd

With normal fuel configuration for a short flight (Center Tank empty and left and right tank 70%) you will see the lights on after loading the aircraft. You have to switch the pumps off. Best regardsStefan

"I've always wondered why on the 737NG (any model) overhead panel as implemented, indicator warning lights for the center fuel tanks are always off regardless of the state of their respective pump switches."The Boeing philosophy is such that amber/yellow and red are associated with abnormalities and attention should be paid to lights of that colour. At some point, CWT(Center Wing Tank) pumps have to be switched off to prevent the pumps overheating in an empty tank. With the CWT empty and the CWT pumps off, you don't really want to see amber pressure lights shining on the overhead panel (in this normal situation).This aside, previous messages on the subject of fuel pumps can be found using the Forum search function (and the possibility that indication anomalies may exist).Cheers.Ian.

Thanks for your replies!It still doesn't make sense to me why the center tank low pressure warning would behave somewhat differently from the other tanks, but I now understand the behavior of the panel.I guess I was considering the low pressure warning more as an indicator of pumps being on or off, which of course it isn't.Oh, and I read somewhere that the center tank should always contain some fuel, about 1,000lb or so slushing around, not used as a reserve mind you, just to keep fuel in there. Not sure what Boeing recommends.Cheers,

Hi Etienne,>It still doesn't make sense to me why the center tank low>pressure warning would behave somewhat differently from the>other tanks, but I now understand the behavior of the panel.>I guess I was considering the low pressure warning more as an>indicator of pumps being on or off, which of course it isn't.--: From Tim Metzinger's excellent tutorial, I found this: " ... the center tank has a gravity feed pickup, and the low-pressure lights for the center tank will only illuminate when the tanks are empty.">Oh, and I read somewhere that the center tank should always>contain some fuel, about 1,000lb or so slushing around, not>used as a reserve mind you, just to keep fuel in there. Not>sure what Boeing recommends.--: This according to Tim is "to cover the wiring in the tank and is the amount required to do so."The only explanation I have as to why is that I seem to remember that it prevents the possibility of sparking within the tank, which could happen if it remains empty or if the wires are exposed - but you may have to check that :-)cheers,Ronniehttp://ronnie.vandelaak.com/baw644.gif