Air carrier flight crew reported a fuel leak enroute at cruise altitude and continued to their destination due to lack of suitable alternates.
Synopsis
Air carrier flight crew reported a fuel leak enroute at cruise altitude and continued to their destination due to lack of suitable alternates.
Narrative
At the time this fuel leak began; I was finishing up my break and was in the bunk. Just before the end of my break; the captain called me and asked me to come back to the flight deck. Upon arrival; I found that the captain and relief pilot were working a possible fuel leak and had already contacted dispatch and Maintenance Control. The captain and relief pilot brought me up to speed on what was going on. It was my understanding that there were some conflicting indications on fuel levels. They had run the suspected fuel leak checklist and had switched over to the totalizer as opposed to calculated fuel. As I watched; the overall fuel level indications fluctuated up and down a few hundred pounds. I resumed my pilot flying duties and ran the radios as the captain and relief officer continued to work the problem; but stayed in the loop with all communications from the crew; maintenance and dispatch. Following the most conservative course; we treated this as a fuel leak and continue to monitor the indications and work with dispatch; operations; and maintenance over the next couple hours. We maintained our division of flying duties per safe procedure. We discussed as a crew and in conjunction with maintenance and dispatch on sat radio during several calls whether to divert; and if so; where. It was clear from dispatch and operations that there were no good alternatives for diversion on our route of flight. Foggy weather as the sun began to rise as well as unknown airports that company does not serve with little to no services available and unknown safety aspects presented a major problem for diversion. Dispatch agreed with us that there were only bad options but that proceeding to ZZZZ while monitoring potential alternatives along the way was our 'best bad option.' The fuel level continued to reduce; but in a stable manner. We continued with our plan over the next little while to continue toward ZZZZ with several airports along the way in mind for diversion if things became critical. When we got to ZZZZ airspace; we [requested priority handling] and landed normally and without incident. My recollection is having slightly more than 10;000 pounds total with a little more than 2000 pounds in the tank that seem to be leaking. It should be noted that when we turned off the runway and proceeded to the gate; the fuel level in the leaking tank which had been steady in its decline up till now during flight suddenly dropped drastically on the ground as we taxied in; and after parking; one could see a trail of fuel leading back toward the runway from under the engine. The ground crew noted the same fuel leak from the left engine area. Despite having advised ATC; no emergency services met the aircraft upon arrival. Soon; after getting off the aircraft; we noticed that a firetruck showed up and began spraying the fuel under the engine in an attempt to disperse it.
Second reporter narrative
Just prior to swap out and slightly after the critical point; enroute to ZZZZ. We received a Fuel Disagree warning. I was the Relief Pilot in the Pilot flying position; so the Captain started working the checklist we noted a fuel imbalance heavy toward the right. We also noted approx 5k difference in calculated verse totalizer. Upon finishing the checklist; I woke up the First Officer about 9 min early to have him there when we contacted dispatch with a maintenance patch. Maintenance Control confirmed the imbalance and was unsure of what was exactly happening. Working with Dispatch (who brought in several others I cannot remember everyone). As a group we discussed the viability of each alternate pro and cons. When we talked with dispatch and updated our alternates. It was remarked that the alternates would not have any servicing capabilities at that hour. We elected to monitor the fuel and seeing that we would land at ZZZZ; with less than desired fuel; but with and nearer alternate of ZZZZ1. The fuel bounced around several times; as we had totalizer selected IAW (In Accordance With) the Checklist. Shortly before going feet dry we got a Fuel Imbalance warning. We followed the checklist however with the we did not balance because of the suspected fuel leak IAW with the Checklist. 10.3 is what I calculated just using minutes since the incident started and time left to fly and how low we were low at every point after the incident. We still had ZZZZ2. And ZZZZ3 if things got worse. That was our biggest concern; as the fuel burn plus loss wasn't showing on new dataor any gauges. I continued to update the Captain on what I thought we would get to ZZZZ with; while watching the tanks to see if there was any rapid changes. We had several not very good options; and approaching each the crew would go over the facts and come to a conclusion before disregarding an diversion. Upon passing ZZZZ1 toward ZZZZ the Capt [requested priority handling] with ZZZZ approach. I continued to monitor; with Capt and back up the FO on the radios (just due to poor quality radios in the region). Near final we received we received a fuel low warning the Capt and I went through the checklist while the first officer flew the approach. Approach and landing were uneventful; taxi was also uneventful; until we noticed we lost 700lb on 3 min of taxi and were able to verify the leak in the glass window panes of the terminal. We were not met by firetruck and had a normal shutdown; noting all the fuels and the asymmetry we landed with.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.