Date: 201311
Local time of day: 0601-1200
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 Distribution System
Component problem: Improperly Operated; Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain
Human factors: Human-Machine Interface
Second reporter function: First Officer
Anomaly: Aircraft Equipment Problem Critical
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Landed As Precaution; Flight Crew Diverted; General Maintenance Action; General Declared Emergency
Contributing factors: Aircraft; Human Factors
Primary problem: Ambiguous

Narrative: On preflight walk around; fluid was noted under number two engine. Contract Maintenance came and we did an engine run on number two engine. No problems noted. Near cruise level off; I opened the fuel crossfeed valve and turned on the left center tank fuel pump as we had 500 LBS fuel in the center tank. The left center tank fuel low pressure light stayed illuminated. I turned off the left center fuel boost pump and turned on the right center tank boost pump. The right center tank fuel low pressure light stayed illuminated. I stopped trying to burn the fuel in the center tank. A few minutes later; the Fuel Imbalance warning illuminated. The right tank was 1;000 LBS low. I had not closed the fuel crossfeed valve. I left the crossfeed valve open and turned off the right main tank fuel pumps. I watched the fuel quantity gauges to verify that the imbalance was being corrected. After a few minutes; there was no difference in the left quantity and the right quantity was continuing to decrease. I alerted the First Officer to the problem and explained what had transpired. We reviewed the Fuel Imbalance QRH Checklist. As a precaution; we also reviewed the Engine Fuel Leak Checklist; which did not seem to apply. We were not using fuel at an excessive rate. We were not able to crossfeed and the imbalance was increasing. We contacted Dispatch and explained the problem. It was a mutual agreement to divert. We declared an emergency and landed without incident. Subsequent testing by Maintenance resulted in no discrepancies with the airplane. Try to ignore distractions during fuel operations.


Second narrative: During the preflight inspection; I noticed fluid I believed to be oil pooled under the #2 engine. The Captain contacted Maintenance Control and had Contract Maintenance come out to the aircraft. The Mechanic stated it was hydraulic fluid; dripping at a slow rate; and directed an engine run to check for leaks. After the engine run; he said there were no more drips. We departed about 20 minutes late; but expected an ontime arrival due to lack of deice and no departure delays. A while after reaching cruise altitude; the Captain noticed a fuel imbalance in excess of 1;000 LBS; with the #2 Engine being lower. He proceeded to crossfeed to rebalance the fuel; but after several minutes; the fuel imbalance continued to grow to approximately 1;400 LBS. I did see the #1 main pumps both on and both #2 main pumps off. The crossfeed was open. I cannot say with certainty the CROSSFEED light was on dim; but it was not bright. During this time; the quantity of fuel in the #1 tank did not decrease. The Captain then turned the crossfeed off. We were in the process of accomplishing the Fuel Imbalance Checklist. Given an unknown fuel issue and unable to control the balance; we elected to divert. The Captain coordinated with Dispatch while I declared an emergency with Center and got vectors. I initiated a descent and; as a precaution only; reviewed the Engine Fuel Leak Checklist. We did not accomplish it. Coordination for support was accomplished and after landing the rescue response found no indications of a leak. We taxied to the gate.


Synopsis: B737-700 flight crew experiences a fuel imbalance after attempting to use 500 LBS remaining in the center tank and forgetting to turn the crossfeed off when no fuel can be used. When the imbalance is noted the fuel pumps for the low wing are turned off but the imbalance appears to grow worse. The flight diverts to a suitable airport but Maintenance can find no discrepancy.