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Fuel Leak + crossfeeds

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Doing a flight from EGLL to Funchal, Madeira Over France, I got a warning that there was a fuel imbalance. The left fuel tanks seemed to be losing fuel at a much higher rate than the right. APU was off. On investigation, crossfeeds were closed, all fuel pumps (bar centre, no fuel in centre) were open. No matter if I closed the fuel pumps on the left the fuel leak continued.This raises the questions, is the T777 programmed to produce faults from time to time, or am I missing something else ?Activating the crossfeeds didn't seem to help.Any ideas ?Also, if i want to transfer fuel from the left to the right or vice versa which crossfeeds need to be opened ?ThanksDavid P.

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DOH !!!It's me. I forgot I had fspassengers running. I suspect it is that that caused the fuel leak (have it set to 10% probability of failure)But, the question still remains. How do the crossfeeds work ?Thanksdp

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Normally, the fuel in the left tank will provide fuel to the left engine, and fuel in the right tank will feed the right engine. The crossfeeds allow fuel from the right tank to feed the left engine and vice versa. This is how you would correct a fuel imabalnce.You wouldn't be transfering fuel from one tank to another. What you would be doing is turning off the pumps in the tank with less fuel in, so it doesn't feed any of the engines, and allowing the tank with more fuel in feed both engines.For example - say I had 40T in the left tank, and 30T in the right tank, and wanted to correct the imbalance. Normally, the right tank feeds the right engine, left tank feeds the left engine. I turn on the crossfeeds, then turn off the pumps for right (30T) tank. The right tank is now isolated and is not feeding fuel to either engines, as the pumps are switched off. But with the crossfeeds open, the fuel from the left left (40T) tank is able to provide fuel to both engines (the fuel feeds across from left to right, hence cross feed). I would then wait for the fuel in the left tank to reach 30T, then activate the pumps in the right tank, and close the crossfeeds.Also, if a fuel leak is suspected, you should never open the crossfeeds. Fuel from the good side would then be able to feed across to the leak side, and leak out. This happened some years back to an Airbus over the atlantic. The pilots didn't suspect a leak, and open the crossfeeds to correct an imbalance. Their error caused ALL of the fuel to leak out, and they managed to glide to an island in the middle of the atlantic.-Phil

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Just for your info - I tried the system sometime ago and PSS 777 crossfeed works fine as advertised above.John R

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