FUEL IMBALANCE DIAGNOSIS

Fuel Quantity Indicator error annunciation?
Yes > NNC FUEL QTY IND INOP
No > Crossfeed (was) open?
Yes > With all Main Tank Fuel Boost Pumps ON different fuel pump output pressure may still cause a substantial fuel imbalance.

No > Takeoff with less than 1,000 kg or 2,000 lbs fuel in the CRT Tank and the CTR Tank Fuel pumps ON, may cause a substantial imbalance because the left pump runs dry while the other pump delivers fuel during climb

Set equal %N1 - Disengage A/P
Set aileron and rudder trim neutral
wings not level
Compare FU(Fuel Used) between engines
wings level (with significant imbalance)
Fuel Qty Ind. malfunction
> NNC FUEL QTY IND INOP

Compare FU between engines
FU equal
Using fuel from CTR tank?
FU not equal
Compare FF (Fuel Flow) and EGT
IF EGT not equal(and imbalance is limited)
Engines have a different fuel consumption
Fuel leak btwn FF-transmitter and Engine Fuel Nozzle
> NNC [ENGINE FUEL LEAK]
Accomplish the engine shutdown Fuel from all tanks is available for single engine.
When Fuel Qty in both tanks is back to balance, open crossfeed to maintain balance and to use all available fuel
Do not use FMC fuel predictions on single engine!

Using fuel from CRT Tank?
Yes CRT and Main Tank Qty decrasing at same rate, equal to FF per one engine?
No NNC [ENGINE FAILURE AND SHUTDOWN]
Yes CRT Tank fuel pump output pressure is lower than Main Tank fuel pump output pressure, or CTR Tank fuel pump is not ON : Switch Main Tank Fuel Boost Pumps to OFF
No NNC [ENGINE FAILURE AND SHUTDOWN]

Verify fuel leak after engine shutdown
Leak stops
Leak in engine pylon btwn Spar Fuel SOV and FF - transmitter
NNC [ENGINE FUEL LEAK]
The engine remains shutdown. Fuel from all tanks is available for single engine. When fuel qty in both tanks is back to balance, open crossfeed to maintain balance and to use all available fuel. For single engine, reduce FMC fuel predictions by 5%.

Have the cabin crew or a nearby airplane visually check for any fuel leak.

Leak continues
  Switch affected Main Fuel Tank Boost Pumps to OFF
   Leak continues at same rate Fuel leak in Main Tank
   Consider an engine relight You can run 2 engines from the remain main tank or the center tank with the crossfeed open.
Leak rate reduces Fuel leak in pipelines to Spar Fuel SOV
Keep crossfeed closed!
Consider an engine relight using fuel from main tank until engine fuel starvation.