737NG Center Tank?

[michal 44]

So in real life they don't land the 737 with any fuel in the center tank?

That would be probably a wrong conclusion. I think after TWA800, precisely because of the danger of explosion, some fuel must be left in the central tank, all pumps must be submerged and there is some sort of minimum amount of fuel you must have in the central tank. I don't know about exact numbers for the 737. Nothing to do with CG of course.

[Hawk777th 0]

Ya I didn't mean bone dry but low fuel sure their would be noway to get all the gas out of it.

[stevenp 1]

I thought it was for redundancy. Can't you fly the plane with no pumps on in the wings? And just gravity feed the fuel to the wings?

[CLett737 14]

From the FCOM: Fuel PumpsEach fuel tank uses two AC powered fuel pumps which are cooled and lubricatedby fuel passing through the pump. Center tank pumps produce higher pressurethan main tank pumps. This ensures that center tank fuel is used before main tankfuel, even though all fuel pumps are operating. Individual pressure sensorsmonitor the output pressure of each pump.[Option - with Center Tank Fuel Pump Auto-shutoff]Each center tank pump will automatically shut off, after a short delay, when thatpump’s sensor detects low output pressure. Now I dont know whether pmdg added the auto shutoff system in the center tank for this feature to work.

[Etai Charit 0]

The fuel is taken from the center tank until it's completely empty, only then from the wing tanks. The Master Causion will illuminate with "Fuel" indication. The Center tank fuel pumps low pressure will illuminate whilest the pump is on. The pumps would NOT TURN OFF AUTOMATICALLY so you must switch to off so they won't overheat and may fail or worse. There's a method to avoid the Master Caution disturbing warning, if you are already aware that the tank is almost empty (about 50 kg left): Open the Cross-Feed Valve and turn off one of the Center Fuel Pumps. Thus you won't get the Master Caution, everything's calm, and both engines would still dry out the center tank before feeding from the wings. When the center tank is fully empty, the remaining pump low pressure light will illuminate, so switch the pump off and close back the cross-feed.

[Nixon 30]

The reason that the centre tank fuel is used first is to relieve the bending moments on the wings. When a plane is on the ground gravity acts through the undercarriage. Therefore the wings act as cantilevers and the wing tips will bend downwards. In flight of course the fuselage is supported by the wings and therefore gravity will tend to push the fuselage down. By using the centre fuel first this effect reduces as the fuel reduces.RegardsNixon Thomas

[KriVa 307]

The fuel is taken from the center tank until it's completely empty, only then from the wing tanks. The Master Causion will illuminate with "Fuel" indication. The Center tank fuel pumps low pressure will illuminate whilest the pump is on. The pumps would NOT TURN OFF AUTOMATICALLY so you must switch to off so they won't overheat and may fail or worse. There's a method to avoid the Master Caution disturbing warning, if you are already aware that the tank is almost empty (about 50 kg left): Open the Cross-Feed Valve and turn off one of the Center Fuel Pumps. Thus you won't get the Master Caution, everything's calm, and both engines would still dry out the center tank before feeding from the wings. When the center tank is fully empty, the remaining pump low pressure light will illuminate, so switch the pump off and close back the cross-feed.

The FCOM clearly states the center pumps do shut off automatically. Although, that wasn't the case with older planes, the new ones sure do.

[Etai Charit 0]

From the FCOM: Fuel PumpsEach fuel tank uses two AC powered fuel pumps which are cooled and lubricatedby fuel passing through the pump. Center tank pumps produce higher pressurethan main tank pumps. This ensures that center tank fuel is used before main tankfuel, even though all fuel pumps are operating. Individual pressure sensorsmonitor the output pressure of each pump.[Option - with Center Tank Fuel Pump Auto-shutoff]Each center tank pump will automatically shut off, after a short delay, when thatpump’s sensor detects low output pressure. Now I dont know whether pmdg added the auto shutoff system in the center tank for this feature to work.

Different than the system I know, probobly like said before a newer pumps and/or logic. Most of the NG's, at least the old ones are as described, with no auto-shut of the pumps, so it is important to switch them off when low pressure is lit. About landing with a certain amount on the center tank - according to specific company procedures, all in all there's no safety instruction or rule. I know to empty it completely. By that logic, indeed landing with fuel in the center tank is a planning mistake and/or system operation error.

[CLett737 14]

Actually I think nick pointed that out in one of his videos that the plane was fitted with the auto shut off system. This was implemented because if the pilots forgot to turn off the center pumps once they were emptied, the pumps would overheat and explode the tank due to residual fuel vapour. I THINK that's why.

[KriVa 307]

After a bit more research... The auto-shut-off feature has been used since May 2004 :(

[Etai Charit 0]

After a bit more research... The auto-shut-off feature has been used since May 2004

Good to keep up. Thanks mate.

[Jack_C 1]

Hey all. Here's some procedures. If you are at the gate with more than 5000 pounds of fuel in the centre, then turn all 6 pumps on. If you have less than 5000 in the centre, turn the centre tank pumps on to prime them, then off. If you have less than 1000 in the centre, centre tank pumps off. So if you have 4000 pounds in centre, prime the pumps then turn them off. Then climbing through 10,000, turn centre pumps on until 1000 pounds then off. The reason you have the centre pumps off up to 10,000 with less than 5000 pounds is the deck angle (while climbing at 250 kts) can still potentially leave the centre pumps uncovered. Once you lower the nose, climbing through 10,000 the theory is the deck angle is low enough for fuel to cover the pumps again.....so they say. The NGX doesn't "incorporate" a nitrogen generation system so you would turn the centre pumps off at all times when below 1000 pounds. JackColwill

[CLett737 14]

With the main tank fuel pump No. 1 FWD Switch ON, the center tank fuelscavenge jet pump operates automatically to transfer any remaining center tankfuel to main tank No. 1. Fuel transfer begins when main tank No. 1 quantity isabout one-half. Once the fuel scavenge process begins, it continues for theremainder of the flight.

[Jack_C 1]

With the main tank fuel pump No. 1 FWD Switch ON, the center tank fuelscavenge jet pump operates automatically to transfer any remaining center tankfuel to main tank No. 1. Fuel transfer begins when main tank No. 1 quantity isabout one-half. Once the fuel scavenge process begins, it continues for theremainder of the flight.

Yes, but what are you saying? JackColwill

[CLett737 14]

Sorry I forgot to ask the question. But now I cant remember what it was.