I have seen this often. I get a yellow FUEL LOW CENTER message on the upper EICAS. So I turn off the center fuel pumps. Then a few minutes later FUEL IN CENTER. Make up your mind Boeing! Is this a bug?

 

 

have a read of fcom2    12.10.7 gives you the indications  and errors of  fuel indications

have a read of fcom2    12.10.7 gives you the indications  and errors of  fuel indications

 

I know what they mean, I am wondering why it tells me to turn off center fuel pumps then minutes later says to turn them back on because there is fuel in the center.

Varying fuel levels on the sensors. Just leave the pumps off, the jet pumps will empty the center tank in due course.

I have seen this often. I get a yellow FUEL LOW CENTER message on the upper EICAS. So I turn off the center fuel pumps. Then a few minutes later FUEL IN CENTER. Make up your mind Boeing! Is this a bug?

 

Does this happen inflight or on the ground?

I think there is a difference between fuel low and empty.  If i remember correctly you get the fuel low message first followed by a low pressure thats when i turn it off. 

 

Marc. 

This is accurate and occurs on the real airplane if you run the tanks that low. The fuel is sloshing and momentarily uncovering the fuel level sensor enough to trigger it.

 

Most airline SOPs require the pumps to be shut off with a sizable amount of fuel still left in the center tanks. (TWA800 rule)

This is accurate and occurs on the real airplane if you run the tanks that low. The fuel is sloshing and momentarily uncovering the fuel level sensor enough to trigger it.

 

Most airline SOPs require the pumps to be shut off with a sizable amount of fuel still left in the center tanks. (TWA800 rule)

wouldn't that result in an "Fuel in center" message?

 

I also thought the center fuel tanks were running dry by their own without the pumps running. I know it isn't at a fast rate but at what amount should this be then?

 

Lucky for me there are still days that this forum teaches me new stuff. thanks Tabs.

wouldn't that result in an "Fuel in center" message?

 

No.

On the 777-200 we dont turn on the center pumps unless there is 4800kg or more fuel in them.

The system is smart and the "Fuel in Center" message is inhibited untill several minutes after departure (dont know exactly but feels like 10minutes).

With more than those 4800KG of fuel in the center tank I think "Fuel in Center" message is not inhibited I think.

I also thought the center fuel tanks were running dry by their own without the pumps running. I know it isn't at a fast rate but at what amount should this be then?

 

You have to look up that value in the Fuel chapter. But yes you are correct. After you have turned off the center pumps you will see a little bit fuel remaining in the center tank (like 1000kg). When the fuel in the wing tanks goes down below a certain level (something like 13.000Kg or so on the 777-200) that little bit of fuel is sucked out of the center tank by a so called scavenge system and pumped into the main tanks.

I have seen this often. I get a yellow FUEL LOW CENTER message on the upper EICAS. So I turn off the center fuel pumps. Then a few minutes later FUEL IN CENTER. Make up your mind Boeing! Is this a bug?

Can you give us the details of your flight?

Like climb/cruise/descend and how much fuel you had.

 

It is probably normal.

When you are in climb and get the "fuel low center" that is because you dont have a lot of fuel in the tanks and because of your pitch up attitude it is in the back of your tank.

When you then turn them pumps off and subsequently level off the plane, the fuel spreads evenly in the tank again so the sensors pick up the correct fuel level and thus you get "fuel in center".

 

That is exactly why you dont turn the center pumps on with little fuel in the center tanks.

To avoid these nuisance messages.

No.

On the 777-200 we dont turn on the center pumps unless there is 4800kg or more fuel in them.

The system is smart and the "Fuel in Center" message is inhibited untill several minutes after departure (dont know exactly but feels like 10minutes).

With more than those 4800KG of fuel in the center tank I think "Fuel in Center" message is not inhibited I think.

You have to look up that value in the Fuel chapter. But yes you are correct. After you have turned off the center pumps you will see a little bit fuel remaining in the center tank (like 1000kg). When the fuel in the wing tanks goes down below a certain level (something like 13.000Kg or so on the 777-200) that little bit of fuel is sucked out of the center tank by a so called scavenge system and pumped into the main tanks.

Can you give us the details of your flight?

Like climb/cruise/descend and how much fuel you had.

 

It is probably normal.

When you are in climb and get the "fuel low center" that is because you dont have a lot of fuel in the tanks and because of your pitch up attitude it is in the back of your tank.

When you then turn them pumps off and subsequently level off the plane, the fuel spreads evenly in the tank again so the sensors pick up the correct fuel level and thus you get "fuel in center".

 

That is exactly why you dont turn the center pumps on with little fuel in the center tanks.

To avoid these nuisance messages.

 

So do you turn on the fuel pumps when it says "Fuel in Centre"

Do you turn it off when it says "Fuel low centre"

 

Do you turn it on and off and on and off and on and off cycling through on and back off several times on and off till it finally stops telling you to turn the pumps on and then off again all the on and off***ing time? (on off)

 

I usually only encounter this issue several hours into a long flight where I had centre tank fuel.

 

Obviously I don't encounter this issue when I take-off with no intention of using whatever fuel, if any, is in the centre tank.

 

Flights of more than 10ish hours seem to be the sweet spot. Usually the centre tank off is in level flight at FL3x0

 

Usually I let it trick me once, then just ignore centre tank low till I'm less than about 300kg in centre tank. Then off it goes for the rest of flight.

 

... It is possible that all of the times that I have seen it, that I have been inside ActiveSky Next injected turbulence.

And that on all occasions it was between 2am and 4am (my house/bedroom) local time whereby I had been asleep for a bit, and had an alarm set for when my fuel state was within 1000kg of empty centre tank.

Found on real fcom:

 

Fuel Pump Operations

 

Before start, the main tank pump switches should all be pushed ON.

Before start, with center tank quantity more than 4,800 kilograms, the center tank

switches should be pushed ON.

During flight, when the FUEL IN CENTER message displays the center tank

pump switches should be pushed ON, when the FUEL LOW CENTER message

displays the center tank pump switches should be pushed off. The condition

statements for these messages are contained in Section 12.30, Fuel System EICAS

Messages.

If a center pump has low output pressure, the fuel pump switch PRESS light

illuminates and the message FUEL PUMP CENTER (L or R) displays.

 

-200ER

With the main tank pumps ON, a scavenge system operates automatically to

transfer any remaining center tank fuel to the main tanks. Fuel transfer begins

when either main tank quantity is less than 13,100 kilograms. Center tank quantity

must be below 15,900 kilograms.

-300ER

With the main tank pumps ON, a scavenge system operates automatically to

transfer any remaining center tank fuel to the main tanks. Fuel transfer begins

when either main tank quantity is less than 23,900 kilograms. Center tank quantity

must be below 15,900 kilograms

So do you turn on the fuel pumps when it says "Fuel in Centre"

Do you turn it off when it says "Fuel low centre"

 

yes

Do you turn it on and off and on and off and on and off cycling through on and back off several times on and off till it finally stops telling you to turn the pumps on and then off again all the on and off***ing time? (on off)

No, that is not normal.