Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft; Human Factors; Procedure
Our aircraft had [a] deferral for the right inner tank fuel quantity indication. We had no working cockpit indication for the fuel quantity in that tank. The MEL requires an alternate means of verifying fuel tank quantity prior to each flight. A logbook entry is required by maintenance to confirm that the fuel quantity in that tank is known. The logbook on this flight was properly signed off by the mechanic verifying a known quantity in the tank with the deferral. During pre-flight; the First Officer compared what he believed to be the fuel remaining from our inbound flight that morning to the fuel added; based on the new fuel slip. He believed that there should have been more fuel onboard than was indicated by the computed total we were given. We talked with the mechanic on duty and asked him about this possible difference. He was very certain that the quantity in the right inner tank was confirmed.He said that there is a digital quantity indication on the re-fueling panel that was working; and confirmed the correct total in that tank. The First Officer said he remembers the mechanic also talking about sticking that tank to confirm the quantity. I don't remember hearing that; but I may have been out of my seat at that moment. The mechanic was adamant that the quantity was right. I've interacted with this mechanic many times over the years; and he is very conscientious. In the end; we had to trust the people that physically check the quantity. We knew that if there were a discrepancy; it would be on the conservative side. We would have more; not less fuel than planned. After takeoff; I immediately noticed that the aircraft wanted to roll to the right. It was easily controllable; but noticeable. This continued throughout the flight; and made me suspect that there may have been more fuel in the right inner tank than was indicated. I decided to make a logbook entry stating that I thought there might be extra fuel in that tank. I suggested that maintenance completely drain that tank and re-fill it to a known quantity for the next flight. I didn't want to pass on a possible discrepancy to the next crew.It would be interesting to know what the actual fuel quantity was in that tank. If it turns out that there was more fuel in that tank than we realized; I can see one possible way that it happened. We receive little; if any training on the re-fueling panel; so I don't know much about how it works. It seems to me that the mechanic was relying mainly on the digital quantity indication on that panel to determine fuel in the right inner tank. Is it possible that the digital indication is actually a fuel counter that measures the amount of fuel added; instead of measuring the total fuel in the tank? If so; that could explain a discrepancy. I'm not sure if the mechanic that we worked with is the one who oversaw the re-fueling of the airplane. It may have been done earlier with a different mechanic. I'm filing this report in the interest of advancing safety. Maybe we can learn something from this.
Air Carrier Captain reported an issue with the fuel quantity gauge with one fuel tank which was deferred by Maintenance. Crew was unsure of the actual quantity in the tank.