B727 CREW LANDED WITH FUEL IMBAL CAUSED BY FUEL XFEED VALVE LEAKAGE.

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SUSPECT WE LANDED WITH FUEL IMBAL EXCEEDING A LIMITATION DUE TO A PROBABLE FUEL XFEED VALVE/FUEL QUANTITY INDICATOR MALFUNCTION. WE WERE ORIGINALLY DISPATCHED WITH A RELEASE FUEL OF 24000 LBS. AFTER ACFT FUELING; TANK QUANTITY GAUGES READ AS FOLLOWS: TANK #1 = 8140 LBS; TANK #2 = 8120 LBS; TANK #3 = 8200 LBS. THE SO'S FUEL PANEL WAS SET UP WITH THE #2 XFEED MANIFOLD VALVE OPEN; AND #1 AND #3 CLOSED (PER SOPA/FUEL DISTRIBUTION). AFTER PUSHBACK; WE ACCOMPLISHED A DELAYED ENG START (OF ENGS #1 AND #2) AND TAXIED TO RWY 25L AT LAX. WE STARTED ENG #3 APPROX 5-8 MINS PRIOR TO TKOF AS SUBSEQUENTLY OUR RWY WAS CHANGED TO RWY 25R. 20 MINS ELAPSED FROM INITIAL BRAKE RELEASE TO WHEELS UP; BUT ON INITIAL PUSHBACK WE WAITED UNTIL THE TUG WAS AT A COMPLETE STOP AND BRAKES RESET BEFORE STARTING THE ENGS AS THE PUSH WAS UP GRADE. CLBING THROUGH APPROX FL190; THE SO STATED SOMETHING WAS NOT RIGHT WITH THE FUEL; AND HE SUSPECTED THE #1 FUEL QUANTITY GAUGE WAS MALFUNCTIONING. IT READ 8300 LBS. THE FUEL IN TANK #2 WAS 7200 LBS AND TANK #3 READ 6000 LBS. AS WE HAD DELAYED STARTING THE #3 ENG; WE WERE NOT SURE WHY TANK #3 WAS INDICATING LESS THAN TANK #2 -- OR WHY TANK #1 INDICATED MORE THAN OUR PUSHBACK FUEL. THE XFEEDS IN TANKS #1 AND #3 WERE STILL CLOSED AND #2 OPEN. WE TESTED AND MONITORED ALL GAUGES FOR 3-4 MINS. I WAS NOT CONVINCED TANK #1 GAUGE WAS RELIABLE. WE TESTED FUEL BURNS AND QUANTITY INDICATIONS FOR ALL 3 ENGS. WE MONITORED FUEL BURN FROM #3 ENG FIRST AND CALCULATED FUEL USAGE BASED ON TIME. IT CHKED OUT. THEN WE XFED 400 LBS FROM TANK #3 TO ENG #2 TO NOTE THE QUANTITY IN THOSE TANKS. CONSUMPTION AND INDICATIONS WERE NORMAL. AT THIS TIME; TANK #1 QUANTITY STARTED TO DECREASE FROM 8300 LBS TO 7900 LBS. WE THEN XFED TANK #1 TO ENG #2. WE MONITORED TIME AND FUEL FLOW AGAIN AND QUANTITIES DIMINISHED AT A PLAUSIBLE RATE. WE NOTED THAT THE XFEED VALVE POS INDICATOR LIGHTS WORKED 'AS PUBLISHED (IN AGREEMENT)' WHEN SELECTED. HOWEVER; TANK #1 INDICATED A QUANTITY 2400 LBS GREATER THAN TANK #3 (TANK #1 - 7900 LBS; TANK #2 = 4800 LBS; TANK #3 - 5500 LBS) AT THAT TIME. MY EXPERIENCE ON THE B727 HAS SHOWN ME THAT FUEL QUANTITY GAUGES ARE MORE PRONE TO INACCURACY THAN XFEED VALVE POS INDICATORS -- AND/OR THE VALVE OP ITSELF. SO I WAS NOT ENTIRELY CONVINCED THAT THE #1 GAUGE WAS INDEED RELIABLE. THEREFORE; I WAS RELUCTANT TO EVENLY BAL TANKS #1 AND #3. TANK #1 HAD INDICATED 200 LBS MORE AT LEVELOFF THAN AT TKOF. I WAS CONCERNED THAT TANK #1 MAY ACTUALLY HAVE LESS FUEL THAN DEPICTED (BASED ON TIME AND BURN) AND I DID NOT WANT TO RUN THE TANK DRY! SOME R AILERON TRIM WAS REQUIRED; AND AFTER DISCUSSION; WE BEGAN TO THINK THAT PERHAPS TANK #1 MIGHT HAVE MORE FUEL THAN TANKS #2 AND #3. AT THIS TIME THOUGH; WE WERE ON THE DSCNT INTO SMF AND STILL NOT CONVINCED THE FUEL GAUGES WERE PROVIDING ACCURATE DATA. AS THE REMAINING FLT SEGMENT WAS SHORT; I ELECTED TO XFEED ANOTHER 600 LBS FROM TANK #1 TO ENG #2 -- BUT AS A RESULT; THE LIMITATION OF 1000 LBS IMBAL BTWN TANKS #1 AND #3 WAS EXCEEDED. WE CALLED SMF AND REQUESTED THAT THE FUEL TRUCK AND A MECH MEET OUR ACFT; SO WE COULD DETERMINE THE SOURCE OF THE IMBAL. IN THE ARR AREA; I HAND FLEW THE ACFT TO VERIFY ITS CTLABILITY AND NOTED NO PROBS. THE ACFT USED LESS THAN 1 UNIT OF R AILERON TRIM AND A SMALLER AMOUNT OF R RUDDER TRIM. THE WX WAS CAVOK AND LIGHTS WINDS (140-160 DEGS AT 6 KTS). IT WOULD BE SAFE TO LAND WITH A POSSIBLE (AND NOT POSITIVELY CONFIRMED) IMBAL. I PREFERRED THAT OPTION; IN CASE THE GAUGE WAS INACCURATE -- AND DID NOT WANT TO USE ANY MORE FUEL THAN I HAD TO FROM TANK #1. AT THE GATE; WE MET WITH THE FUELER AND MECH AND CONFIRMED THE WING TANK TOTAL. THEY MATCHED THE SO'S COCKPIT GAUGES INDICATIONS. THUS; UPON COMPLETION OF THE FLT; OUR TANK QUANTITIES WERE 6000 LBS; 3500 LBS; 4000 LBS. THE MECH ALSO STUCK THE WING TANKS LATER AND STATED THAT TANK #1 HAD MORE THAN 3. IT WAS SUSPECTED THAT THE #1 FUEL XFEED VALVE MAY HAVE FAILED PARTIALLY OPEN EVEN THOUGH THE VALVE POS (AGREEMENT) LIGHT CONSISTENTLY MATCHED PLACEMENT WITH THE SWITCH. THIS WOULD FURTHER EXPLAIN THE IMBAL. NO PERSON OR ACFT WAS HARMED; YET A LIMITATION WAS EXCEEDED -- ONE THAT UNDER NORMAL CIRCUMSTANCES WOULD NOT HAVE BEEN. HOWEVER; WITH THE INFO AVAILABLE TO US AT THE TIME ENRTE; I FELT IT WISER AND A SAFER COURSE OF ACTION TO HAVE A MANAGEABLE IMBAL RATHER THAN AN ENG FAIL DUE TO A FAULTY FUEL GAUGE AND FUEL STARVATION.