MYSTERIOUS FUEL BURN PROBLEM ON AN LGT DURING CLIMB. ENGINES #1 AND #2 REPORTEDLY SET TANK TO ENGINE BURNED FUEL FROM #2 TANK.

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THIS RPT COVERS A PERCEIVED MALFUNCTION W/IN THE FUEL SYS. WHERE FUEL WAS BEING DRAWN FROM ONLY 1 TANK; BY OBSERVING THE FUEL QTY INDICATORS; WHEN THE COCKPIT FUEL PANEL WAS CALLING FOR FUEL FEED FROM ALL 3 TANKS TO THEIR RESPECTIVE ENGS. THE PROB WAS FIRST CALLED TO MY ATTN BY THE S/O AS WE CLBED THROUGH FL190 FOR FL220. AT TKOF; THE FUEL QTY INDICATORS READ 7200; 7400; 7300 #. THEY NOW READ 7000; 3800; 7000 #. ALL THE FUEL WAS COMING FROM THE #2 TANK. THE FUEL PANEL WAS IN THE NORMAL CONFIGN; I.E.; ALL PUMPS ON; #1 AND #3 XFEED VALVE SWITCHES OFF AND #2 XFEED VALVE SWITCH OPEN. I OBSERVED A DECREASE IN THE #2 FUEL QTY INDICATION EQUIVALENT TO THE BURN OF ALL 3 ENGS AND NO DECREASE IN THE QTY INDICATORS OF THE #1 AND #3 TANKS. WHEN THE #2 PUMPS WERE TURNED OFF FOR 2 MIN; A DECREASE IN THE FUEL QTY INDICATIONS WAS SEEN IN ALL 3 FUEL QTY INDICATORS. IT WAS DETERMINED THAT FUEL FROM #1 AND #3 TANKS COULD BE USED TO FEED THE #2 ENG. WITH SITUATION STABILIZED; THE FLT OPERATED IN SOMEWHAT NORMAL TANK TO ENG CONFIGN EXCEPT FOR THE #2 TANK PUMPS OFF. SOMETHING HAD HAPPENED! IMMEDIATE FOCUS WAS ON THE #1 AND #3 XFEED VALVE SWITCH POS DURING CLB. THE S/O STATES POSITIVELY THAT THESE VALVES WERE NOT IN ANY OTHER POS DURING CLB THEN CLOSED. I HAVE NO KNOWLEDGE OR BELIEF TO DISBELIEVE HIS STATEMENT. THE S/O FURTHER STATES THAT IF HE HAD HAD THESE VALVES OPEN DURING CLB; HE WOULD HAVE ADMITTED THIS AS THIS IS NOT THAT BIG OF A PROB. EXCEPT IF IT LED TO ENG FLAME OUT. AGAIN; IF A MISTAKE HAD BEEN MADE AT THE S/O PANEL; IT COULD HAVE BEEN QUICKLY AND QUIETLY RECTIFIED BY HIM ALONE; POSSIBLY EVEN W/O MY KNOWLEDGE. THIS ACFT IS EQUIPPED WITH STD FUEL PUMPS AND SO; IF THE XFEEDS ARE OPEN AND ALL PUMPS ARE ON; VERY LITTLE IF ANY XFEEDING IS SUPPOSED TO OCCUR UNTIL ANOTHER TANK'S PUMPS HAVE BEEN TURNED OFF. SOMETHING HAPPENED! I HAVE NO KNOWLEDGE IF ANYTHING LIKE THIS HAS EVER HAPPENED BEFORE. IF SO; WHO WOULD KNOW; AND WHAT WAS THE PROB? THE ACFT FUEL SYS WAS CHKED W/O FINDING ANY MALFUNCTION. NOT THE FIRST TIME THAT A SYS HAS GND CHKED OK! I FLEW THIS ACFT 3 MORE LEGS THAT DAY W/O A RECURRENCE.