Thanks for your reply mate.
most unlikely, and if it is the APU causing the 'imbalance' (40kg per hour - you must have very good eyesight!!) then it happens pumps on or off.
I'm a little picky and try to be a perfectionist.
I guess an imbalance of 6 to 8 kg is nothing to be worried about. This is when using the AFT1 pump.
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One more question. If the amount of fuel in the CTR tank exceeds 5,000 kg, are the CTR tank pumps turned off prior to takeoff?