The FAA issued AD says that you must NOT have the centre tank pumps on unless you have 1000 LBS (453 KGS) minimum in the centre tank, except for defuelling or transferring. Also any time they are on, you must have someone in the cockpit monitoring them, and you must turn them off as soon as the low pressure lights come on.
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"I USED to be a PPRuNaholic, but now I'm CURED"