Air China fuel bonus is based on the amount of extra fuel you have in the tanks on arrival beyond the flight plan estimate.
SO
They simply load an extra 1500KG on departure, over burn about 500KG on a 10 hour sector carrying the extra fuel, then land at destination with 1000KG over plan and hey presto, you get a fuel bonus.
Its scary that they have a fuel saving bonus that ACTUALLY burns MORE fuel and they dont get it!!!!