Narrative:

The EICAS 'low fuel' caution illuminated. The QRH was followed; dispatch notified and the captain recalled to the flight deck. After further analysis and consultation with dispatch; maintenance and the company; a decision was made to divert. Clearance was obtained and the flight made an uneventful approach and landing. Details; including our thought process and concerns we have. The 'bunky' was the pilot flying; the flying first officer (first officer) monitoring and the captain was on break. The EICAS 'low fuel' caution illuminated. The QRH was pulled out and the index drove the pilots to the low fuel procedure. Fuel quantities were compared between the totalizer; and the flight plan fuel. A leak not indicated by this check. The checklist does not provide for ignoring a low fuel caution. With this in mind and suspecting it was a spurious EICAS; I asked maintenance if he would approve of me performing a fuel quantity system test utilizing the test switch on the maintenance panel adjacent to the observer's seat. The fuel system was reconfigured to a normal configuration and the test accomplished. The low fuel light remained. The test was retried about another minute later which resulted in the low fuel message disappearing; but the illumination of a fuel configuration message. At this point a 1000lb imbalance was observed between the left and right main tanks. From pictures I had taken; a fuel imbalance of 600lbs occurred in less than 7 minutes. This fuel imbalance continued to increase rather quickly to a high of 1500lbs with the cross feeds closed. Since the use of the fuel quantity test was not an authorized step in the QRH procedure and because of the increasing fuel imbalance; the consensus was that a divert was the most prudent course of action; and quite possibly the only 'legal' course of action. Based on the indications we were receiving; we elected at this point to leave the fuel panel in a normal configuration vs all pumps on and cross feeds open as called for the QRH for low fuel. (Remember the low fuel message had gone away too). Furthermore; since there was still a possibility we had a fuel leak; we elected not to balance fuel. At the point the decision to divert was agreed upon; we terminated the connection with dispatch to concentrate on the divert. I turned on all exterior lights; chose heading select and began a turn 45 degrees left of our current heading. The pilot monitoring (pm) broadcast our intensions. The relief pilot continued to monitor the fuel gauges (easiest view from his seat). In the FMC we chose a 10nm offset. Crossing the 10nm line we began a descent from FL350 to FL345. We then inserted; executed and turned to follow a 15nm offset left of course while trying to obtain clearance from center. The clearance process was rather difficult. Center attempted HF SELCAL on both the primary and backup frequencies. We could not initially establish comms on either HF. Another aircraft did help with relay. We finally got a clearance to descend to FL340 and proceed direct. In VHF comms we were cleared direct [for] the ILS. During the divert the fuel imbalance fluctuated between 600lbs and 1500lbs with the fuel configuration light and caution on the whole time. (The 'bunky' was closely monitoring fuel the entire way). A normal; uneventful approach and landing was made. Maintenance and a fueler met the aircraft. The tanks were dipped; fueled; redipped and quantities verified. The aircraft was also inspected for leaks and a byte test run on the fuel system. The crew and the company agreed it was safe to continue. The company and the 117 desk were consulted about crew legalities. Since the captain had obtained a full 90 minute rest prior to the divert and there would be opportunity for the flying first officer to obtain rest during the next leg; we elected to have the flying first officer become the pilot flying (PF) for the leg to [destination]. We believe this complied with both the intent and the letter of the law as described byfar 117 and the associated rulings; interpretations and exemptions. Although I felt good; we decided it was a better option to have the flying first officer be the pilot flying for the [final] leg. A normal flight was made. The fuel system operated normally and there were no fluctuations in the fuel quantity or balance.

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Original NASA ASRS Text

Title: B767 flight crew reported observing a 'Low Fuel' caution light at cruise altitude on an oceanic flight. Troubleshooting procedures yielded ambiguous results; and a successful diversion to a suitable airport was accomplished.

Narrative: The EICAS 'Low Fuel' caution illuminated. The QRH was followed; dispatch notified and the Captain recalled to the flight deck. After further analysis and consultation with Dispatch; Maintenance and the Company; a decision was made to divert. Clearance was obtained and the flight made an uneventful approach and landing. Details; including our thought process and concerns we have. The 'bunky' was the pilot flying; the flying First Officer (FO) monitoring and the Captain was on break. The EICAS 'Low Fuel' caution illuminated. The QRH was pulled out and the index drove the pilots to the LOW FUEL procedure. Fuel quantities were compared between the totalizer; and the flight plan fuel. A leak not indicated by this check. The checklist does not provide for ignoring a Low Fuel caution. With this in mind and suspecting it was a spurious EICAS; I asked Maintenance if he would approve of me performing a fuel quantity system test utilizing the test switch on the maintenance panel adjacent to the observer's seat. The fuel system was reconfigured to a normal configuration and the test accomplished. The low fuel light remained. The test was retried about another minute later which resulted in the Low Fuel message disappearing; but the illumination of a Fuel Configuration message. At this point a 1000lb imbalance was observed between the left and right main tanks. From pictures I had taken; a fuel imbalance of 600lbs occurred in less than 7 minutes. This fuel imbalance continued to increase rather quickly to a high of 1500lbs with the cross feeds closed. Since the use of the fuel quantity test was not an authorized step in the QRH procedure and because of the increasing fuel imbalance; the consensus was that a divert was the most prudent course of action; and quite possibly the only 'legal' course of action. Based on the indications we were receiving; we elected at this point to leave the fuel panel in a normal configuration vs all pumps on and cross feeds open as called for the QRH for low fuel. (Remember the low fuel message had gone away too). Furthermore; since there was still a possibility we had a fuel leak; we elected NOT to balance fuel. At the point the decision to divert was agreed upon; we terminated the connection with dispatch to concentrate on the divert. I turned on all exterior lights; chose heading select and began a turn 45 degrees left of our current heading. The Pilot Monitoring (PM) broadcast our intensions. The relief pilot continued to monitor the fuel gauges (easiest view from his seat). In the FMC we chose a 10nm offset. Crossing the 10nm line we began a descent from FL350 to FL345. We then inserted; executed and turned to follow a 15nm offset left of course while trying to obtain clearance from Center. The clearance process was rather difficult. Center attempted HF SELCAL on both the primary and backup frequencies. We could not initially establish comms on either HF. Another Aircraft did help with relay. We finally got a clearance to descend to FL340 and proceed direct. In VHF comms we were cleared direct [for] the ILS. During the divert the fuel imbalance fluctuated between 600lbs and 1500lbs with the fuel configuration light and caution on the whole time. (The 'bunky' was closely monitoring fuel the entire way). A normal; uneventful approach and landing was made. Maintenance and a fueler met the aircraft. The tanks were dipped; fueled; redipped and quantities verified. The aircraft was also inspected for leaks and a byte test run on the fuel system. The crew and the company agreed it was safe to continue. The Company and the 117 desk were consulted about crew legalities. Since the Captain had obtained a full 90 minute rest prior to the divert and there would be opportunity for the flying FO to obtain rest during the next leg; we elected to have the flying FO become the Pilot Flying (PF) for the leg to [destination]. We believe this complied with both the intent and the letter of the law as described byFAR 117 and the associated rulings; interpretations and exemptions. Although I felt good; we decided it was a better option to have the flying FO be the Pilot Flying for the [final] leg. A normal flight was made. The fuel system operated normally and there were no fluctuations in the fuel quantity or balance.

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.