MD-80 Series (DC-9-80) Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Fuel Issue
Flight Crew Became Reoriented; General Maintenance Action
Aircraft
During cruise flight; we observed that the quantity of fuel in all three fuel tanks (both wings and center) was decreasing simultaneously. This was a fuel management burn which did not comply with the normal procedure of emptying the fuel from the center tank prior to using main tank fuel (DC-9 Op. Man. Vol. 1; LIMITATIONS.) There is not a procedure in the QRH which specifically addresses the issue of all three fuel tank quantities decreasing simultaneously. The center tank pumps checked normal on preflight;therefore; we assumed that the center pumps were operating but supplying a lower pressure than normal. We performed the QRH procedure 'Fuel Not Feeding from Center Tank or Center Tank Fuel Pump Inoperative'. We employed the procedure as though the center tank quantity was not decreasing -- otherwise; the procedure states 'Continue normal operations' and we would have accomplished nothing. Although fuel was feeding from the center tank; had we continued flight without performing this procedure we would have landed with a significant amount of fuel in the center tank and the wing tanks well below full. We were able to reduce the center tank quantity to 700 LBS. employing this procedure and we didn't use any fuel from the wing tanks during the time we were employing the procedure. The center tank quantity continued to decrease after we completed the procedure; and the center tank was empty prior to landing. The approach and landing were uneventful. During the entire flight all other systems operated normally. As I previously mentioned; there wasn't a procedure in the QRH pertaining to this condition. Although the center tank pumps were operative; I suspect that they weren't supplying the pressure sufficient to ensure that the engines would feed from the center tank alone. We therefore employed the procedure that we did to ensure that the center tank emptied prior to burning any more fuel from the main tanks to comply with the limitation previously listed. This was performed in the interest of safety. I believe it was the safest and the proper action to take.
At cruise altitude observed fuel not feeding from center tank. Wing tank fuel quantities were decreasing when center tank should have been only fuel quantity that was decreasing. Executed QRH for 'Fuel Not Feeding from Center Tank.' QRH procedure resolved problem; flight continued uneventfully to destination. It's my understanding that the Captain wrote up the issue at the destination.
MD80 flight crew reports fuel decreasing in both wing tanks and the center tank during cruise when only the center tank should be decreasing. The QRH procedure for fuel not feeding from the center tank is employed to ensure most center tank fuel is used before turning the wing tank pumps back on.