A300 flight crew reported an unexplained decrease in right outer fuel quantity and diverted.

Attributes
ACN	1421162
Time
Date	201701
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	A300
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Component
Aircraft Component	Fuel Tank
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Inflight Event / Encounter Fuel Issue

Narrative:

Passing 18;000 on climbout noticed an unexplained decrease in right outer fuel quantity. Followed QRH procedures for fuel feed manual control and fuel leak. Did not confirm a fuel leak but right outer quantity continued to decrease. Right outer [fuel quantity] should not have burned down at all. After completing fuel feed manual control with center pumps off to ensure fuel was burning from inner tanks right outer continued to decrease. Entered fuel leak checklist and did not confirm a fuel leak because only indication was an imbalance but fuel total continued to burn down on pace with flight plan release. Consulted with [maintenance] and airbus tech pilot. Diverted to nearest airport. Aircraft landed exceeding outer wing tank limits; no problems noted. On the ground with engines shutdown and no fuel pumps on; right outer continued to decrease quantity over a one hour period.

Original NASA ASRS Text

Title: A300 flight crew reported an unexplained decrease in right outer fuel quantity and diverted.

Narrative: Passing 18;000 on climbout noticed an unexplained decrease in right outer fuel quantity. Followed QRH procedures for fuel feed manual control and fuel leak. Did not confirm a fuel leak but right outer quantity continued to decrease. Right outer [fuel quantity] should not have burned down at all. After completing fuel feed manual control with center pumps off to ensure fuel was burning from inner tanks right outer continued to decrease. Entered fuel leak checklist and did not confirm a fuel leak because only indication was an imbalance but fuel total continued to burn down on pace with flight plan release. Consulted with [Maintenance] and Airbus tech pilot. Diverted to nearest airport. Aircraft landed exceeding outer wing tank limits; no problems noted. On the ground with engines shutdown and no fuel pumps on; right outer continued to decrease quantity over a one hour period.

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.