A300 flight crew reported noticing a right outer fuel tank imbalance during cruise. The crew ran all the appropriate checklists and after talking to company operations; they decided to divert.
Synopsis
A300 flight crew reported noticing a right outer fuel tank imbalance during cruise. The crew ran all the appropriate checklists and after talking to company operations; they decided to divert.
Narrative
As Captain I was PF. At Top of climb; we noticed there was an abnormal fuel imbalance with outer tanks. Right outer tank was ~1000 LBS less than the Left outer. We compared FOB with expected top of climb fuel as well as weight and balance; and Fuel slip. We continued to monitor fuel as we passed the next couple of waypoints to verify no fuel leak per QRH as well as a possible fuel gauge issue. At each waypoint we checked the total FOB was correct which led us to believe we had an auto fuel feed issue or pump pressure issue but no fault indications were present. Via Radio; we consulted with Operations Control/Maintenance Control which also consulted with Flight Operations. We reviewed QRH procedures for Fuel Imbalance as well as followed QRH procedures for Manual Fuel Feed. At direction of Maintenance we Pulled/Reset prescribed CB (auto fuel feed) in QRH procedure and later in flight we pulled and left open same circuit breaker to try and disable the fuel feed system all together. First officer was PM during event keeping and manually computing current and expected fuel burn and communicating with ATC. ACARS communication was split depending upon task at hand. I communicated with company via Radio as necessary and maintained control of aircraft. We worked QRH procedures together using a flight operations team on the ground; systems knowledge; and manual calculations. We requested our Dispatcher come up with an alternate plan in case we could not get our issue fixed. By the time all known available options had been explored; a decision was made to divert to ZZZ which was directly off our nose and a familiar airport. We [requested priority handling] for precautionary reasons at landing due to limitation excedence of fuel imbalance. Landed with no issues. We may have been able to divert sooner however we had to try something and wait to see if we could isolate our issue. After agreeing we did not want to increase our fuel disparity we executed our divert plan. We landed with a 3500 LB fuel imbalance.Cause - Malfunction in fuel system.
Second reporter narrative
At cruise we noticed a right outer fuel tank fuel imbalance of 1;100 pounds less than the left outer tank; 7.8 (Left) vs 6.7 (Right). During cruise we kept a log every ten minutes to determine if there was a potential fuel leak and to track its trend; if any. As we monitored the Right Outer Tank; we noticed a slow but continuous decrease in fuel quantity.We ran the Fuel Leak checklist in the QRH and we determined there was no fuel leak based on fuel used plus current fob; estimated fuel on arrival; and our in-flight fuel log which was showing an extra 100 pounds on arrival.We also referenced the Fuel Imbalance/ X-Feed In Flight checklist in the QRH. The procedures applied mostly to inner tanks balancing and even states 'It is not recommended to attempt balancing fuel between the Outer Tanks.'Lastly; we looked at the Fuel Feed Manual Control QRH checklist. We went to manual control and fed from the center tank until empty but still had a decreasing Right Outer Fuel tank quantity. At this point; we determined we were burning fuel out of the right outer by 900 pounds/hour. We used Radio to discuss with Operations Control and Maintenance Control. Maintenance Control thought it was an auto fuel feed issue and per Maintenance Control and QRH Fuel Feed Manual Control we pulled the AUTO FUEL FEED CB. We were still burning at the same rate from Right Outer tank after circuit breaker was pulled. At this point; we determined we exhausted all options and estimated we would land in ZZZ with 3400 pounds in the right outer tank and with a 4800 pound imbalance. We elected to [request priority handling] and divert to ZZZ1 to prevent a larger/uncontrollable imbalance landing with a fuel imbalance of 3500 pounds. Cause - Fuel system malfunction.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.