MD-11 Captain and Dispatcher reported a loss of fuel quantity during cruise. Flight crew diverted and landed safely.
Synopsis
MD-11 Captain and Dispatcher reported a loss of fuel quantity during cruise. Flight crew diverted and landed safely.
Narrative
Approximately 3 hours into flight; approaching ZZZZ at FL 340; received a Level 2 FUEL QTY/USED CHK alert. Approximately 50 minutes earlier at ZZZ; a fuel log entry was made indicating the flight was 2 minutes behind; but up 2.3K on the fuel. Crossing ZZZZZ; the flight was still 2 minutes behind; but down 6.9K on the fuel. Aircrew complied with QRH. When system was switched to manual and the Tail tank was isolated; the tail tank continued to decrease 400lbs in 4 minutes. Suspect the fuel leak was in or connected to the Tail tank. After consulting with Dispatch and Maintenance Control via SATCOM; [requesting priority handling] and making a diversion to ZZZ1 was the safest course of action. An uneventful landing was made on Runway XXL. After landing; the emergency ground crew inspected the aft end of the aircraft and noted a slow drip from the left side of the tail. The difference between our blockout fuel minus the fuel used and the total fuel on board at block-in was 14;280 lbs.Cause: Not sure. Maintenance is still trying to figure that out. The fuel system malfunctioned.Suggestions: Perhaps some sort of inflight diagnostic and fuel leak isolation logic.
Second reporter narrative
Inflight diversion / [Requested priority handling]. XA:04Z - Crew called on Satcom with a fuel concern. Level 2 Fuel Quantity Check / Possible Fuel Leak. Reported 10;000 pounds of fuel lost over the last hour. Phone patch established with Currently use Maintenance Control. Currently use Maintenance Control asked questions to determine if it was an indication issue. It was thought to be a real fuel leak. Fuel transfer out of the tail tank was still in progress. Crew suspected that the fuel leak was related to the tail tank or the related plumbing. We considered continuing if the fuel loss stabilized after the transfer was complete. I ran numbers with 93;000 pounds of estimated fuel over waypoint ZZZZZ and 2.7% overburn. We were far short of meeting the ETP scenario. We elected to divert. Diverted to ZZZ as it was just ahead and the preference for maintenance and tail swap. I learned after landing that the crew [requested priority handling]. [Requested priority handling] due to possibility of fuel leaking on to hot brakes. Fire trucks inspected the aircraft after clearing Runway XXL. Minor fuel leak near tail noted. Aircraft taxied to gate under own power.Cause: Maintenance issue; suspected fuel leak in flight.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.