Narrative:

After personally experiencing over 7 fuel gauge errors and knowing of at least 4 other fuel-related events and errors at this airline since 2002; I am well-aware of the fact that the airplane's fuel gauges aren't always an accurate reflection of the actual fuel state inside the fuel tanks. Because of this I believe it is important to perform some type of verified uplift calculations. I received the fueling slip directly from the fueler as is customary. The fueling slip indicated that 13280 liters had been pumped aboard the aircraft. I then converted this amount to gals (3508 gals) and then I multiplied the gals added of 3508 by 6.7 and I reached a figure of 23500 pounds pumped aboard the jet. By adding 23500 pounds of fuel pumped to an ACARS foa of 9300 pounds I had a sum of 32800 pounds; yet my gauges only indicated 30000 pounds for an error of an additional 2800 pounds of fuel aboard the jet; which could not be readily explained. After reworking my numbers and reaching the same result several times; my initial impression was possibly I had made an error in converting the liters to gals; yet upon reworking my calculations I continued reaching the same conversion of liters to gals. My next step in the troubleshooting process was to evaluate the fueling slip for errors. After inspecting the slip; I discovered there was a 10 liter error on the slip which I considered to be a de minimis amount so I continued trying to find an explanation for the 2800 pound error prior to contacting maintenance. The next step in the process was to determine if possibly there was a starting point listed on the fueling slip for a prior-to-fueling fuel load. Unfortunately this wasn't located on the slip so I contacted operations in order to verify the foa. Operations confirmed a foa (fuel on arrival) of 9300 pounds as indicated on the ACARS legs page so I then proceeded to inquire about departure fuel which operations said was 20600 pounds. Fortunately the inbound crew had not reset the fuel totalizers as many crews do so I was able to determine that the inbound flight had burned 7110 pounds on engine #1 and 7130 pounds on engine #2 for a total fuel burn of 14240 pounds. When I subtracted the fuel burn of 14240 pounds from the departure fuel of 20600 pounds I got a result of 6360 pounds of an arrival fuel; yet when I added the burn of 14240 pounds of the fuel totalizers to the ACARS foa of 9300 pounds I got a result of 23540 pounds in spite of the fact operations says they showed a departure fuel of 20600 pounds for a difference of 2940 pounds. By now I was not sure whether we had a fuel gauge error; but to be conservative and most of all safe I contacted maintenance and placed a write-up in the maintenance log. A maintenance technician arrived and within a few mins of troubleshooting he began suspecting that possibly there was an error made by the inbound crew when entering the foa into ACARS. He theorized that perhaps the inbound crew hit a '9' rather than a '6' on the ACARS keypad when entering foa; which could possibly explain the foa of 9300 pounds. Had there been a starting fuel point listed on the fueling slip it would have been much easier to solve this riddle but since the fuel slip did not provide such information it really complicated the troubleshooting process. I then spoke with maintenance control and they began to agree with the maintenance technician that perhaps the inbound crew entered an incorrect foa of 9300 pounds into ACARS rather than what they suspected as what should have been a correct amount of 6300 pounds. Maintenance told me they reached this conclusion after working with both dispatch and operations in order to obtain arrival and departure readings; along with gals added on several legs that aircraft had last flown. After carefully performing calculations they concluded that the foa should have most likely been 6300 pounds versus the 9300 pounds entered into ACARS by the inbound crew. After hearing their explanation I began to agree that the problem was very likely the result of an incorrect foa entered by the inbound crew. In spite of feeling confident that their theory was correct; maintenance control still felt that it would be prudent to xfer fuel from the mains into the center tank until hitting vto (volume top off; ie full tank) and then read the center tank gauge in order to see if there were any errors. (Both wing tanks had been drip-sticked and the results confirmed that both the #1 and #2 gauges were functioning properly.) fuel xfer was done and the center tank passed the test. Ultimately it was assumed that the inbound crew must have entered an incorrect foa so a fuel gauge error was ruled out as a problem and we departed 116 mins late. While my xchks of the fuel gauges may go above and beyond what the company thinks I should be doing; I believe it is well within reason to perform these xchks considering past errors that this technique has detected. According to a required bulletin; 'the captain shall ensure minimum fuel requirements are met and maximum takeoff and landing weights are not exceeded.' since I have more than enough evidence from past experience indicating that our fuel gauges are not always as accurate or reliable as we would like them to be; I believe it's more than prudent to use every resource at my disposal to comply with the above referenced bulletin in order to ensure that each flight I command meets fuel requirements without exceeding maximum takeoff and landing weights. I believe this company needs to have some alternative procedure for insuring that the fuel pumped aboard is indeed what the fuel gauges indicate. At the minimum we should receive some type of fueling slip from the fueler as we used to do for yrs before the slip was eliminated not long after 9/11. Also; it would be nice for the fueler to record the arrival fuel; followed by the final departure fuel; along with gals/liters added so that crews can have every tool at their disposal to ensure that what the gauges read is indeed a correct fuel load. ACARS arrival fuel should be automatically sent via ACARS in order to eliminate possible human error as we experienced.

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Original NASA ASRS Text

Title: B737 CAPTAIN SUSPECTS FUEL GAUGE ERROR WHEN ARRIVAL FUEL AND UPLIFT FUEL DO NOT EQUAL GAUGE FUEL. ERROR IS TRACED TO INACCURATE ACARS ENTRY BY ARRIVAL CREW. REPORTER BELIEVES FUEL SLIP SHOULD SHOW START FUEL AND UPLIFT.

Narrative: AFTER PERSONALLY EXPERIENCING OVER 7 FUEL GAUGE ERRORS AND KNOWING OF AT LEAST 4 OTHER FUEL-RELATED EVENTS AND ERRORS AT THIS AIRLINE SINCE 2002; I AM WELL-AWARE OF THE FACT THAT THE AIRPLANE'S FUEL GAUGES AREN'T ALWAYS AN ACCURATE REFLECTION OF THE ACTUAL FUEL STATE INSIDE THE FUEL TANKS. BECAUSE OF THIS I BELIEVE IT IS IMPORTANT TO PERFORM SOME TYPE OF VERIFIED UPLIFT CALCULATIONS. I RECEIVED THE FUELING SLIP DIRECTLY FROM THE FUELER AS IS CUSTOMARY. THE FUELING SLIP INDICATED THAT 13280 LITERS HAD BEEN PUMPED ABOARD THE ACFT. I THEN CONVERTED THIS AMOUNT TO GALS (3508 GALS) AND THEN I MULTIPLIED THE GALS ADDED OF 3508 BY 6.7 AND I REACHED A FIGURE OF 23500 LBS PUMPED ABOARD THE JET. BY ADDING 23500 LBS OF FUEL PUMPED TO AN ACARS FOA OF 9300 LBS I HAD A SUM OF 32800 LBS; YET MY GAUGES ONLY INDICATED 30000 LBS FOR AN ERROR OF AN ADDITIONAL 2800 LBS OF FUEL ABOARD THE JET; WHICH COULD NOT BE READILY EXPLAINED. AFTER REWORKING MY NUMBERS AND REACHING THE SAME RESULT SEVERAL TIMES; MY INITIAL IMPRESSION WAS POSSIBLY I HAD MADE AN ERROR IN CONVERTING THE LITERS TO GALS; YET UPON REWORKING MY CALCULATIONS I CONTINUED REACHING THE SAME CONVERSION OF LITERS TO GALS. MY NEXT STEP IN THE TROUBLESHOOTING PROCESS WAS TO EVALUATE THE FUELING SLIP FOR ERRORS. AFTER INSPECTING THE SLIP; I DISCOVERED THERE WAS A 10 LITER ERROR ON THE SLIP WHICH I CONSIDERED TO BE A DE MINIMIS AMOUNT SO I CONTINUED TRYING TO FIND AN EXPLANATION FOR THE 2800 LB ERROR PRIOR TO CONTACTING MAINT. THE NEXT STEP IN THE PROCESS WAS TO DETERMINE IF POSSIBLY THERE WAS A STARTING POINT LISTED ON THE FUELING SLIP FOR A PRIOR-TO-FUELING FUEL LOAD. UNFORTUNATELY THIS WASN'T LOCATED ON THE SLIP SO I CONTACTED OPS IN ORDER TO VERIFY THE FOA. OPS CONFIRMED A FOA (FUEL ON ARR) OF 9300 LBS AS INDICATED ON THE ACARS LEGS PAGE SO I THEN PROCEEDED TO INQUIRE ABOUT DEP FUEL WHICH OPS SAID WAS 20600 LBS. FORTUNATELY THE INBOUND CREW HAD NOT RESET THE FUEL TOTALIZERS AS MANY CREWS DO SO I WAS ABLE TO DETERMINE THAT THE INBOUND FLT HAD BURNED 7110 LBS ON ENG #1 AND 7130 LBS ON ENG #2 FOR A TOTAL FUEL BURN OF 14240 LBS. WHEN I SUBTRACTED THE FUEL BURN OF 14240 LBS FROM THE DEP FUEL OF 20600 LBS I GOT A RESULT OF 6360 LBS OF AN ARR FUEL; YET WHEN I ADDED THE BURN OF 14240 LBS OF THE FUEL TOTALIZERS TO THE ACARS FOA OF 9300 LBS I GOT A RESULT OF 23540 LBS IN SPITE OF THE FACT OPS SAYS THEY SHOWED A DEP FUEL OF 20600 LBS FOR A DIFFERENCE OF 2940 LBS. BY NOW I WAS NOT SURE WHETHER WE HAD A FUEL GAUGE ERROR; BUT TO BE CONSERVATIVE AND MOST OF ALL SAFE I CONTACTED MAINT AND PLACED A WRITE-UP IN THE MAINT LOG. A MAINT TECHNICIAN ARRIVED AND WITHIN A FEW MINS OF TROUBLESHOOTING HE BEGAN SUSPECTING THAT POSSIBLY THERE WAS AN ERROR MADE BY THE INBOUND CREW WHEN ENTERING THE FOA INTO ACARS. HE THEORIZED THAT PERHAPS THE INBOUND CREW HIT A '9' RATHER THAN A '6' ON THE ACARS KEYPAD WHEN ENTERING FOA; WHICH COULD POSSIBLY EXPLAIN THE FOA OF 9300 LBS. HAD THERE BEEN A STARTING FUEL POINT LISTED ON THE FUELING SLIP IT WOULD HAVE BEEN MUCH EASIER TO SOLVE THIS RIDDLE BUT SINCE THE FUEL SLIP DID NOT PROVIDE SUCH INFO IT REALLY COMPLICATED THE TROUBLESHOOTING PROCESS. I THEN SPOKE WITH MAINT CTL AND THEY BEGAN TO AGREE WITH THE MAINT TECHNICIAN THAT PERHAPS THE INBOUND CREW ENTERED AN INCORRECT FOA OF 9300 LBS INTO ACARS RATHER THAN WHAT THEY SUSPECTED AS WHAT SHOULD HAVE BEEN A CORRECT AMOUNT OF 6300 LBS. MAINT TOLD ME THEY REACHED THIS CONCLUSION AFTER WORKING WITH BOTH DISPATCH AND OPS IN ORDER TO OBTAIN ARR AND DEP READINGS; ALONG WITH GALS ADDED ON SEVERAL LEGS THAT ACFT HAD LAST FLOWN. AFTER CAREFULLY PERFORMING CALCULATIONS THEY CONCLUDED THAT THE FOA SHOULD HAVE MOST LIKELY BEEN 6300 LBS VERSUS THE 9300 LBS ENTERED INTO ACARS BY THE INBOUND CREW. AFTER HEARING THEIR EXPLANATION I BEGAN TO AGREE THAT THE PROB WAS VERY LIKELY THE RESULT OF AN INCORRECT FOA ENTERED BY THE INBOUND CREW. IN SPITE OF FEELING CONFIDENT THAT THEIR THEORY WAS CORRECT; MAINT CTL STILL FELT THAT IT WOULD BE PRUDENT TO XFER FUEL FROM THE MAINS INTO THE CTR TANK UNTIL HITTING VTO (VOLUME TOP OFF; IE FULL TANK) AND THEN READ THE CTR TANK GAUGE IN ORDER TO SEE IF THERE WERE ANY ERRORS. (BOTH WING TANKS HAD BEEN DRIP-STICKED AND THE RESULTS CONFIRMED THAT BOTH THE #1 AND #2 GAUGES WERE FUNCTIONING PROPERLY.) FUEL XFER WAS DONE AND THE CTR TANK PASSED THE TEST. ULTIMATELY IT WAS ASSUMED THAT THE INBOUND CREW MUST HAVE ENTERED AN INCORRECT FOA SO A FUEL GAUGE ERROR WAS RULED OUT AS A PROB AND WE DEPARTED 116 MINS LATE. WHILE MY XCHKS OF THE FUEL GAUGES MAY GO ABOVE AND BEYOND WHAT THE COMPANY THINKS I SHOULD BE DOING; I BELIEVE IT IS WELL WITHIN REASON TO PERFORM THESE XCHKS CONSIDERING PAST ERRORS THAT THIS TECHNIQUE HAS DETECTED. ACCORDING TO A REQUIRED BULLETIN; 'THE CAPT SHALL ENSURE MINIMUM FUEL REQUIREMENTS ARE MET AND MAX TKOF AND LNDG WTS ARE NOT EXCEEDED.' SINCE I HAVE MORE THAN ENOUGH EVIDENCE FROM PAST EXPERIENCE INDICATING THAT OUR FUEL GAUGES ARE NOT ALWAYS AS ACCURATE OR RELIABLE AS WE WOULD LIKE THEM TO BE; I BELIEVE IT'S MORE THAN PRUDENT TO USE EVERY RESOURCE AT MY DISPOSAL TO COMPLY WITH THE ABOVE REFED BULLETIN IN ORDER TO ENSURE THAT EACH FLT I COMMAND MEETS FUEL REQUIREMENTS WITHOUT EXCEEDING MAX TKOF AND LNDG WTS. I BELIEVE THIS COMPANY NEEDS TO HAVE SOME ALTERNATIVE PROC FOR INSURING THAT THE FUEL PUMPED ABOARD IS INDEED WHAT THE FUEL GAUGES INDICATE. AT THE MINIMUM WE SHOULD RECEIVE SOME TYPE OF FUELING SLIP FROM THE FUELER AS WE USED TO DO FOR YRS BEFORE THE SLIP WAS ELIMINATED NOT LONG AFTER 9/11. ALSO; IT WOULD BE NICE FOR THE FUELER TO RECORD THE ARR FUEL; FOLLOWED BY THE FINAL DEP FUEL; ALONG WITH GALS/LITERS ADDED SO THAT CREWS CAN HAVE EVERY TOOL AT THEIR DISPOSAL TO ENSURE THAT WHAT THE GAUGES READ IS INDEED A CORRECT FUEL LOAD. ACARS ARR FUEL SHOULD BE AUTOMATICALLY SENT VIA ACARS IN ORDER TO ELIMINATE POSSIBLE HUMAN ERROR AS WE EXPERIENCED.

Data retrieved from NASA's ASRS site as of May 2009 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.