Date: 201506
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: Climb
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Fuel Quantity-Pressure Indication
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Troubleshooting
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

Narrative: We arrived from our deadhead to ZZZ and proceeded to the gate and accepted the aircraft. It had just returned to the line from the maintenance hangar where it received an airworthiness inspection the night prior. Other than being hot from being unventilated; the aircraft showed no discrepancies during the preflight. I verified the fuel quantity on the aircraft from the previous night via a fuel audit of the logbook and upload from the Fueler. The amount was within two hundred pounds and was within acceptable limits at 13.3 planned and 13.2 onboard with a minimum takeoff of 12.6. We pushed from the gate and elected to taxi on two engines for the first flight of the day warm up for the engines. We were number one for the departure and received no real delays on taxi out. I verified we were above minimum fuel for takeoff as we neared departure; out take after this point was quick. Upon climbout at approximately 3000 ft; I noticed a fuel imbalance between the number one and number two main tanks of about 1800 pounds with the lower tank being the left. This struck both of us as unrealistic and we started to perform a crossfeed from the right tank and trouble shooting. I had the First Officer check our fuel in the ACARS at takeoff and it indicated we had departed below min fuel at approximately 12.4. We did not at this point believe we had burned 900 pounds on an expeditious taxi when planned for a taxi burn of 300 pounds so we knew a discrepancy of some form or failure had occurred in the fuel system. I transferred the controls and radios to the First Officer and proceeded to use the new Boeing QRH that had been activated that morning. We referenced the Fuel Leak Checklist but I proceeded to the Fuel Quantity Checklist in Chapter 12 quickly when the right quantity indicator then began to spike up and down with readings as low as zero pounds. Dispatch and Maintenance were contacted and were advised of the situation. White waiting on the patch; the numbers were run and we noticed a 1000-pound difference between our last known quantity at the gate and our totalizer fuel burn of the engines. As the flight progressed; this difference extended to 2000 pounds. Our concern became this: we knew 5500 pounds had been uploaded onto the aircraft; and we knew we had an unknown error(s) in our fuel quantity indicators and as such we could not verify how much fuel actually had been on the plane when the upload was made. We knew we would burn in excess of the known 5500 pounds that were uploaded with the continuation to ZZZ1 or a return to ZZZ. Being that we were closer to ZZZ we elected to return. We elected to proceed directly to ZZZ and to remain at a cruse altitude until we could perform a nearly idle flight path to the airport environment. We also elected to open and keep the crossfeed valve open during the descent and landing being unsure as to the remaking fuel in each main tank. Upon reaching the gate uneventfully; I asked Maintenance and they dripped the tanks. The values at the gate were consistent with the quantity indicated upon the gauges. Upon further review; it was determined this aircraft had a previous history with inaccurate fuel reading. It is my assumption that the readings in flight are not consistent with readings of a stationary aircraft on the ground for whatever reason. The First Officer was a great help. He communicated well with me and ATC and was well-skilled. I couldn't have asked for a better Crew and First Officer. I believe the situation was handled well in all regards.




Synopsis: Captain reported observing a fuel burn/imbalance anomaly during climbout. After completing the appropriate fuel system troubleshooting checklists he elected to return to the departure airport and landed uneventfully.