MD80 fuel system
The only thing I can think of is "fuel migration" from center to mains. It's due to leaking one-way check valves as the CTR fuel pressure is higher than the mains with all pumps on, fuel moves to the mains from CTR. MTC manual says 500#/hr migration from CTR to mains is OK...mains to CTR...no migration is allowed...it will ground the airplane. Ask me another question.