Narrative:

We pushed back from the gate with a fuel load of 42;700 pounds. About 45 minutes into the flight; I contacted dispatch to inquire about direct routing. The winds aloft were particularly high and I didn't want to take a direct route if the winds would cause a longer flight time. Dispatch recommended direct mci (kansas city) direct mlp (mullan pass) as filed; for our most efficient routing. Over mci (2 hours and 57 minutes into the flight); we were on time and 200 pounds under burn as we had consistently been so far. About one hour later; we checked our abeam point and we were 3 minutes late and we were 1200 pounds overburn. That got our attention! 1400-pound change in about an hour. Winds were very close to flight plan forecasts throughout the flight. Concerned that we might have a fuel leak; I immediately calculated fuel used and fuel remaining which showed 41;960 pounds. I continued to check the burn vs remaining fuel about every 15 minutes and that number was pretty consistent +/- about 100 pounds. That was about 700 pounds less than we had at pushback; but didn't account completely for the 1400 pound difference. We also had the center tanks run dry during that hour. While it is normal to lose 200 to 300 pounds when the center tanks run dry; this still didn't account for the difference. We also checked the QRH; but this offered no guidance. Fuel flow; fuel used and fuel remaining did not show any anomalies as it would if fuel was leaking. We advised dispatch of the anomaly and continued on. The FMS showed our arrival at sea with a few hundred pounds over our alternate/reserve fuel of 5100 pounds. If this continued to decrease; we would be in close proximity to a suitable airport throughout the rest of the flight if a diversion became necessary. The fuel burn remained consistent between 1200 and 1300 pounds over burn. As we got closer to seattle I asked dispatch if aircraft were being delayed by ATC into seattle. We were told that there were no delays yet. I advised my first officer that we would not accept any turns (delay); but I felt comfortable continuing on to seattle where the weather was 1300 overcast/rain. He agreed.as we were descending into seattle; ATC gave us a right 360 degree turn for delay. I advised him that we were unable. I told him we could slow down; but we could not accept any delay vectors. He complied. We landed in seattle without incident with 5000 pounds of fuel; 1200 pounds over flight plan burn and 100 pounds under our bingo fuel (5100 pounds) and six minutes longer than flight plan. Fuel at the gate was 4700 pounds. Upon arrival at the gate; I consulted with maintenance control and explained what had happened and then entered it in the aircraft logbook.

Related reports:

Google
 

Original NASA ASRS Text

Title: B737-800 Captain reported a possible fuel leak on his transcontinental flight.

Narrative: We pushed back from the gate with a Fuel Load of 42;700 pounds. About 45 minutes into the flight; I contacted Dispatch to inquire about direct routing. The winds aloft were particularly high and I didn't want to take a direct route if the winds would cause a longer flight time. Dispatch recommended Direct MCI (Kansas City) Direct MLP (Mullan Pass) As Filed; for our most efficient routing. Over MCI (2 hours and 57 minutes into the flight); we were on time and 200 pounds under burn as we had consistently been so far. About one hour later; we checked our abeam point and we were 3 minutes late and we were 1200 pounds overburn. That got our attention! 1400-pound change in about an hour. Winds were very close to flight plan forecasts throughout the flight. Concerned that we might have a fuel leak; I immediately calculated Fuel Used and Fuel Remaining which showed 41;960 pounds. I continued to check the burn vs remaining fuel about every 15 minutes and that number was pretty consistent +/- about 100 pounds. That was about 700 pounds less than we had at pushback; but didn't account completely for the 1400 pound difference. We also had the Center Tanks run dry during that hour. While it is normal to lose 200 to 300 pounds when the center tanks run dry; this still didn't account for the difference. We also checked the QRH; but this offered no guidance. Fuel Flow; Fuel Used and Fuel Remaining did not show any anomalies as it would if fuel was leaking. We advised Dispatch of the anomaly and continued on. The FMS showed our arrival at SEA with a few hundred pounds over our alternate/reserve fuel of 5100 pounds. If this continued to decrease; we would be in close proximity to a suitable airport throughout the rest of the flight if a diversion became necessary. The fuel burn remained consistent between 1200 and 1300 pounds over burn. As we got closer to Seattle I asked Dispatch if aircraft were being delayed by ATC into Seattle. We were told that there were no delays yet. I advised my FO that we would not accept any turns (delay); but I felt comfortable continuing on to Seattle where the weather was 1300 overcast/rain. He agreed.As we were descending into Seattle; ATC gave us a right 360 degree turn for delay. I advised him that we were unable. I told him we could slow down; but we could not accept any delay vectors. He complied. We landed in Seattle without incident with 5000 pounds of fuel; 1200 pounds over flight plan burn and 100 pounds under our Bingo fuel (5100 pounds) and six minutes longer than flight plan. Fuel at the gate was 4700 pounds. Upon arrival at the gate; I consulted with Maintenance Control and explained what had happened and then entered it in the Aircraft Logbook.

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.