Date: 201401
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Fuel Crossfeed
Component problem: Design; Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain
Human factors: Communication Breakdown; Distraction; Workload; Troubleshooting; Time Pressure
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew FLC complied w / Automation / Advisory; Flight Crew Diverted; Flight Crew Took Evasive Action
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

Narrative: During climbout; an imbalance in the main fuel tanks was discovered. There was around 2;000 LBS in the center tanks and the main tanks were full at departure. The tanks were now showing around 700 LBS less fuel in the left main tank and decreasing while the right main tank showed an ever so slight decrease. Simultaneously; we sent an ACARS to Dispatch about the situation and consulted the QRH. We felt the most likely culprit was the fuel crossfeed valve and used the Crossfeed Selector Inop Checklist; which directed us to check the circuit breaker. It was found to be tripped.  The next step was to check that sufficient fuel was available to both engines. We determined there was not enough fuel to complete the original 2.5-hours flight. At that time; there was still no word from Dispatch so we used commercial radio to establish contact. While we waited to hear from the Dispatcher; we decided to divert to a much closer Station and advised ATC of our intentions and also advised the Dispatcher as well when we made contact. Passengers were informed and the rest of the flight was uneventful. We landed with an imbalance of approximately 2;600 LBS.

Callback: The reporter stated that the center fuel tank quantity was about 2;000 LBS on takeoff so the pumps were off in accordance with the minimum 5;000 LBS quantity for pumps on during takeoff. During climb; the intent was to open the center tank crossfeed and activate the pumps; but when the reporter looked at the fuel quantity and saw the imbalance; the QRH was referenced. What was confusing about the system indications was that all pumps and valves appeared to be in the correct position with no lights on; including the Fuel Crossfeed blue light out. They were also confused why right tank fuel pumps did not feed direct tank to engine since the pumps appeared to be operational. The only abnormality was the tripped crossfeed circuit breaker. The crew choose not to turn fuel boost pumps off while troubleshooting for fear or flaming an engine out and instead diverted and were assigned a different aircraft for the remained of that trip.Maintenance later stated that the crossfeed cannon plug connector was cleaned; valve operation verified and the aircraft released. One possible explanation for the fuel usage was the crossfeed valve failed either open or partially open and the left wing tank fuel pumps providing a higher output than the right tank; and therefore feeding both engines. The question remained if the crossfeed valved was in a position other than closed when the reporter was ready to commence crossfeed; why was the blue crossfeed light not ON.



Synopsis: A B737-700 crew discovered a fuel imbalance during climbout caused by a fuel crossfeed fault with a circuit breaker tripped so; while completing the QRH; the crew diverted to landed with a 2;600 LBS imbalance as the left main tank was depleting.