dream747
The fuel leak procedure is a bit ritualistic. The procedure LEAK FROM ENGINE/PYLON NOT CONFIRMED or LEAK NOT LOCATED also assumes that there is fuel in center tank. When there is no fuel in the center tank then it is straight forward case of leak from one side because the cross feed is always off and fuel imbalance will also be developing. But still leak can be from engine or tank. Even if leak is from engine it can be from upstream or down stream of fuel flow meter. In case of fuel leak down stream of FF meter the sum total of FU+FOB will match fuel at departure but the FF on that side will be high but in upstream leak case it will not match. So there are variables and to avoid too much thinking and hasty conclusion it is safer to run through the procedure.