An A320 developed about a 1;000 pound inter-tank fuel imbalance which also lowered the arrival fuel....

Attributes
ACN	978035
Time
Date	201111
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Fuel Quantity-Pressure Indication
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical Inflight Event / Encounter Fuel Issue

Narrative:

At cruise altitude of FL320 we noticed fuel 800-1;000 pounds indicating lower on the left wing tank; causing an arrival fuel to drop from 4.4 to 3.4. At this time ATC assigns a vector heading for traffic. I instructed the first officer to decline the heading due to 'minimum fuel' and cannot except any delays at this time. We did not declare an 'minimum fuel emergency' due to arrival fuel was above 30 minutes. We cross checked fuel burn and fuel on board to eliminate possible fuel leak; and continued with cross feeding. Approximately 2 minutes later left fuel tank started to increase fuel pounds; increasing to an arrival fuel of 4.4. ATC declared an emergency for us and gave us direct routing to our destination. We proceeded uneventfully; landed with 4.4 arrival fuel and were meet by maintenance at the gate. Unexplained fuel anomaly.

Original NASA ASRS Text

Title: An A320 developed about a 1;000 pound inter-tank fuel imbalance which also lowered the arrival fuel. After the crew refused a vector for minimum fuel ATC declared their emergency and gave a direct clearance.

Narrative: At cruise altitude of FL320 we noticed fuel 800-1;000 LBS indicating lower on the left wing tank; causing an arrival fuel to drop from 4.4 to 3.4. At this time ATC assigns a vector heading for traffic. I instructed the First Officer to decline the heading due to 'minimum fuel' and cannot except any delays at this time. We did not declare an 'minimum fuel emergency' due to arrival fuel was above 30 minutes. We cross checked fuel burn and fuel on board to eliminate possible fuel leak; and continued with cross feeding. Approximately 2 minutes later left fuel tank started to increase fuel LBS; increasing to an arrival fuel of 4.4. ATC declared an emergency for us and gave us direct routing to our destination. We proceeded uneventfully; landed with 4.4 arrival fuel and were meet by Maintenance at the gate. Unexplained fuel anomaly.

Data retrieved from NASA's ASRS site as of April 2012 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.