Narrative:

Departed gate at stl with 20900 pounds fuel showing on the gauges as follows: #1 - 10000, #2 - 10000, center - 900 pounds. Takeoff with 19800 pounds evenly balanced. Burned off center tank fuel in climb. At about 50 NM past ict the #1 fuel gauge indicated 2000 pounds higher than #2. We had not noticed a large difference before that. The left wing felt heavy when the autoplt was disengaged but, because of moderate turbulence, we were unable to determine the exact trim requirements. I then balanced the fuel by burning the #1 indicated quantity down to the level of #2. (This was a mistake.) because the winds at FL350 were 40-50 KTS worse than flight planned and because of the moderate turbulence, we descended to FL310 and finally to FL280. Everything appeared normal until between abq and zun when the #1 fuel gauge increased to over 10000 pounds and then went totally blank. I cycled the fuel quantity circuit breaker but was unable to get a reading of any kind of the #1 fuel quantity gauge. Finally, in the descent, we got a reading on the #1 fuel quantity gauge of only 500 pounds. The #2 gauge showed 2800 pounds. The FMC showed a total of 4200 pounds but the total of the gauges was only 3300. Assuming the worst and not wanting to risk a flameout on the #1 engine. I immediately began to xfeed from the @3 tank. We called maintenance control and entered a holding pattern near the landing field. I wanted to get the fuel a little closer to the landing imbal limits but I did not want to run the risk of allowing the total to become dangerously low. Maintenance control informed us that the #1 fuel quantity gauge had been written up as unreliable several weeks prior but that they had not been able to duplicate the problem or take any action. I depressed the fuel quantity test button and got #1 = 270 pounds/#2 - 2050 pounds. I cycled the fuel quantity circuit breaker and got #1 = 550 pounds/#2 = 1200 pounds. By that time, the amount of conflicting data had become overwhelming. We did not know what to believe so we landed immediately. On taxi in the readings were #1 = 380 pounds and #2 = 1200 pounds. A maintenance technician immediately came to the cockpit and performed a bite test on the 3 fuel quantity gauges. He reported that all 3 failed the bite test. We were then informed that the #1 fuel tank drip stick tested as 'almost empty.' it now appears that we never really had as much as was indicated at departure. My initial balancing because the fuel gauges showed a 2000 pound split was inappropriate since there was no reason to assume that the fuel had gotten unbalanced. No rules were broken. We are using this report for the reason it was originally designed -- to share information with other pilots so that we might all learn. I suggest that all en route fuel/time/distance log checks be made by adding all tank quantities rather than relying solely on the totalizer. Such a procedure would have shown that the #1 gauge was faulty and that fuel balancing was not advisable. We would not have come so close to running out of fuel in the #1 tank.

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Original NASA ASRS Text

Title: MLG HAS FAULTY FUEL GAUGE SHOWING IMBAL. CALL UP TO MAINT CTL INDICATES WRITTEN UP AS UNRELIABLE.

Narrative: DEPARTED GATE AT STL WITH 20900 POUNDS FUEL SHOWING ON THE GAUGES AS FOLLOWS: #1 - 10000, #2 - 10000, CENTER - 900 POUNDS. TKOF WITH 19800 POUNDS EVENLY BALANCED. BURNED OFF CENTER TANK FUEL IN CLB. AT ABOUT 50 NM PAST ICT THE #1 FUEL GAUGE INDICATED 2000 POUNDS HIGHER THAN #2. WE HAD NOT NOTICED A LARGE DIFFERENCE BEFORE THAT. THE L WING FELT HVY WHEN THE AUTOPLT WAS DISENGAGED BUT, BECAUSE OF MODERATE TURB, WE WERE UNABLE TO DETERMINE THE EXACT TRIM REQUIREMENTS. I THEN BALANCED THE FUEL BY BURNING THE #1 INDICATED QUANTITY DOWN TO THE LEVEL OF #2. (THIS WAS A MISTAKE.) BECAUSE THE WINDS AT FL350 WERE 40-50 KTS WORSE THAN FLT PLANNED AND BECAUSE OF THE MODERATE TURB, WE DSNDED TO FL310 AND FINALLY TO FL280. EVERYTHING APPEARED NORMAL UNTIL BTWN ABQ AND ZUN WHEN THE #1 FUEL GAUGE INCREASED TO OVER 10000 POUNDS AND THEN WENT TOTALLY BLANK. I CYCLED THE FUEL QUANTITY CIRCUIT BREAKER BUT WAS UNABLE TO GET A READING OF ANY KIND OF THE #1 FUEL QUANTITY GAUGE. FINALLY, IN THE DSCNT, WE GOT A READING ON THE #1 FUEL QUANTITY GAUGE OF ONLY 500 POUNDS. THE #2 GAUGE SHOWED 2800 POUNDS. THE FMC SHOWED A TOTAL OF 4200 POUNDS BUT THE TOTAL OF THE GAUGES WAS ONLY 3300. ASSUMING THE WORST AND NOT WANTING TO RISK A FLAMEOUT ON THE #1 ENG. I IMMEDIATELY BEGAN TO XFEED FROM THE @3 TANK. WE CALLED MAINT CTL AND ENTERED A HOLDING PATTERN NEAR THE LNDG FIELD. I WANTED TO GET THE FUEL A LITTLE CLOSER TO THE LNDG IMBAL LIMITS BUT I DID NOT WANT TO RUN THE RISK OF ALLOWING THE TOTAL TO BECOME DANGEROUSLY LOW. MAINT CTL INFORMED US THAT THE #1 FUEL QUANTITY GAUGE HAD BEEN WRITTEN UP AS UNRELIABLE SEVERAL WKS PRIOR BUT THAT THEY HAD NOT BEEN ABLE TO DUPLICATE THE PROBLEM OR TAKE ANY ACTION. I DEPRESSED THE FUEL QUANTITY TEST BUTTON AND GOT #1 = 270 POUNDS/#2 - 2050 POUNDS. I CYCLED THE FUEL QUANTITY CIRCUIT BREAKER AND GOT #1 = 550 POUNDS/#2 = 1200 POUNDS. BY THAT TIME, THE AMOUNT OF CONFLICTING DATA HAD BECOME OVERWHELMING. WE DID NOT KNOW WHAT TO BELIEVE SO WE LANDED IMMEDIATELY. ON TAXI IN THE READINGS WERE #1 = 380 POUNDS AND #2 = 1200 POUNDS. A MAINT TECHNICIAN IMMEDIATELY CAME TO THE COCKPIT AND PERFORMED A BITE TEST ON THE 3 FUEL QUANTITY GAUGES. HE RPTED THAT ALL 3 FAILED THE BITE TEST. WE WERE THEN INFORMED THAT THE #1 FUEL TANK DRIP STICK TESTED AS 'ALMOST EMPTY.' IT NOW APPEARS THAT WE NEVER REALLY HAD AS MUCH AS WAS INDICATED AT DEP. MY INITIAL BALANCING BECAUSE THE FUEL GAUGES SHOWED A 2000 POUND SPLIT WAS INAPPROPRIATE SINCE THERE WAS NO REASON TO ASSUME THAT THE FUEL HAD GOTTEN UNBALANCED. NO RULES WERE BROKEN. WE ARE USING THIS RPT FOR THE REASON IT WAS ORIGINALLY DESIGNED -- TO SHARE INFO WITH OTHER PLTS SO THAT WE MIGHT ALL LEARN. I SUGGEST THAT ALL ENRTE FUEL/TIME/DISTANCE LOG CHKS BE MADE BY ADDING ALL TANK QUANTITIES RATHER THAN RELYING SOLELY ON THE TOTALIZER. SUCH A PROC WOULD HAVE SHOWN THAT THE #1 GAUGE WAS FAULTY AND THAT FUEL BALANCING WAS NOT ADVISABLE. WE WOULD NOT HAVE COME SO CLOSE TO RUNNING OUT OF FUEL IN THE #1 TANK.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.