A B737 captain rebalanced fuel three times in two hours but maintenance found no fuel system anomali...

Narrative:

During our inbound flight we had a steadily increasing fuel imbalance of 30 to 40 pounds per 5 minute time interval. We performed the imbalance checklist and looked at the fuel leak checklist to rule out a leak. The fuel used and the fuel flows were virtually the same on both engine sides. The fuel used plus the fuel on board equaled the boarded fuel. During about 2 hours and 20 minutes of flying we had to rebalance the fuel 3 times for a total rebalancing of about 900 pounds. We wrote the problem up in the logbook and sent a note to maintenance control. After talking with the local mechanics I was shown a maintenance procedure that listed steps to take if the imbalance was 3000 pounds; and other steps if it was 1000 pounds. We were told that since our imbalance was only 900 pounds everything was ok. The procedure does not list any time frames on these limits. Had we flown for another 15 minutes we would have been over 1000 pounds. After I refused the aircraft; maintenance did a crossfeed valve check. I was told the valve was working fine; but after asking further it was only verified to move to its correct positions; it was not checked to see if it was leaking. After I asked the mechanics and maintenance control if anything else could cause the imbalance we saw except for a leaking crossfeed valve; no one had any ideas. I then refused the aircraft out of concern that I would not be able to isolate the fuel system properly during scenarios of leaks; fires; fuel contamination; etc.

Original NASA ASRS Text

Title: A B737 Captain rebalanced fuel three times in two hours but maintenance found no fuel system anomalies to account for the behavior. The crew refused the aircraft because a fuel crossfeed valve leak could not be ruled out.

Narrative: During our inbound flight we had a steadily increasing fuel imbalance of 30 to 40 LBS per 5 minute time interval. We performed the imbalance checklist and looked at the fuel leak checklist to rule out a leak. The fuel used and the fuel flows were virtually the same on both engine sides. The fuel used plus the fuel on board equaled the boarded fuel. During about 2 hours and 20 minutes of flying we had to rebalance the fuel 3 times for a total rebalancing of about 900 pounds. We wrote the problem up in the logbook and sent a note to Maintenance Control. After talking with the local mechanics I was shown a maintenance procedure that listed steps to take if the imbalance was 3000 LBS; and other steps if it was 1000 LBS. We were told that since our imbalance was only 900 LBS everything was OK. The procedure does not list any time frames on these limits. Had we flown for another 15 minutes we would have been over 1000 LBS. After I refused the aircraft; maintenance did a crossfeed valve check. I was told the valve was working fine; but after asking further it was only verified to move to its correct positions; it was not checked to see if it was leaking. After I asked the mechanics and Maintenance Control if anything else could cause the imbalance we saw except for a leaking crossfeed valve; no one had any ideas. I then refused the aircraft out of concern that I would not be able to isolate the fuel system properly during scenarios of leaks; fires; fuel contamination; etc.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1306900
Time
Date	201511
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Other Preflight planning
Flight Plan	IFR
Component
Aircraft Component	Fuel Crossfeed
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 145 Flight Crew Total 14000 Flight Crew Type 423
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy Deviation - Procedural Maintenance Deviation - Procedural Weight And Balance Inflight Event / Encounter Fuel Issue

A B737 captain rebalanced fuel three times in two hours but maintenance found no fuel system anomalies to account for the behavior. The crew refused the aircraft because a fuel crossfeed valve leak could not be ruled out.