Date: 201912
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Aircraft component: Fuel Quantity-Pressure Indication
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: Pre-flight; Aircraft In Service At Gate
Result: General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft; MEL; Procedure
Primary problem: Procedure

Narrative: Aircraft had [an] MEL for Left Fuel Indicator. When I got to the aircraft; fueling was in progress and Maintenance was monitoring the fueling. After fueling they were to stick the tanks and confirm the fuel on board. The original flight plan gate fuel was 32.1 but I ordered a 1000 lbs. increase to have a buffer in case there were any fuel calculation errors.I was estimating that when fueling was complete; there should be approximately 15.7 in the center tank with the main tanks full. The fueling actually stopped with the center at 15.7 and the mains full. However; for some reason; fueling resumed again. I walked out to the Ramp to talk to Maintenance and the Fueler. By the time I was outside; the center tank had 20.0; at which point they stopped fueling. Apparently; prior to fueling; Maintenance 'sticked' the tanks and provided the Fueler with the number of gallons to add. However apparently they made an error and provided the wrong number. The Fueler added the correct amount of gallons based on Maintenance's info which resulted [in] us getting overfueled. When fueling was complete; the fuel slip showed 33.1 as total fuel on board and Maintenance was convinced that this was the correct number.However; I ran my calculations and they were based on the following. The right tank was showing 8.8; which if we are to assume that the left wing is full as well based on sticking the tanks; then the left tank had 8.8. The center tank was showing 20.0. 8.8 +8.8 + 20.0 = 37.6. Again; Maintenance showed 33.1; a 4500 lbs. discrepancy. I'm okay with having extra gas; but not okay being 4500 lbs overweight on a short runway. I asked Maintenance to stick the center tank so we can determine that our flight deck gauge matches the sticks since there was such a large discrepancy between the two totals. First; Maintenance couldn't find the sticks for the center tank. Then they said that the center tank didn't have sticks. I pulled out the flight manual which showed that there were 6 sticks for each main tank and 4 sticks in the center tank. They eventually found the center tank sticks and determined that the center tank had 19;152 lbs. of fuel; much more than 15.7 that should have been there. [It was] still different than what our gauge showed at 20.0. So; we decided to use our total fuel number of 37.6 for any weight related calculations; and the Maintenance number of 36.8 for any fuel remaining calculations to be conservative on both ends. The ZFW (Zero Fuel Weight) turned out to be 1825 under the planned weight which gave us just enough margin to do a full thrust; bleeds off T/O from LGA without having to defuel or remove passengers. Due to the extra work required by Maintenance to calculate fuel and release a Maintenance Release; the flight took a delay of 53 minutes. Arriving in ZZZ 21 minutes late led to some misconnects.In flight; we calculated fuel on board by subtracting fuel used from total at brake release and comparing to the Howgozit. We also estimated left fuel quantity by matching that of the right main tank. The fuel burns and totals were very consistent throughout the flight.Sticking the tanks is an infrequently used procedure and thus can be challenging for the inexperienced Mechanic. But it should not be so challenging for the Mechanic to reach out to Technical Support Maintenance Control or have a clear procedure in a manual to reference. Furthermore; this was an RON airplane and sticking the tanks could have been done well ahead of time and not at boarding time. The Mechanic who sticked the tanks confessed and apologized for his error once he realized that he was wrong. He was also very appreciative of my patience and determination to get the job done right so that there would be no question in anyone's mind about how much fuel was on the airplane.




Synopsis: B737 Captain reported confusion during MEL procedures for determining fuel onboard.