B757-200
Flight Crew Air Transport Pilot (ATP)
Confusion
Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Weight And Balance; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Procedure
On the flight plan there were 3 MELs related to fuel. 1. XX-XX-X Total Fuel Quantity Indication; 2. XX-XX-Y Fuel Tank Quantity Indication Systems (Flight Deck) Main Deck Indicators. This was due to a note in the first MEL. 3. XX-XX-Z Fuel Quantity Indications (Fueling Panel).At the airplane the fuel indications were not blank so the indications were different than the actual because of the MEL. In our situation it was the left main tank that was inoperative. Maintenance gave us a known fuel quantity of 10.7 he derived for the left tank. Tank indications: L C R 10.7 .6  10.4 (derived by maintenance)- 10.7 above 8.7 (indicated). Total 20.3 (indicated). Actual total 21.7. Based on the known fuel quantity maintenance gave us; we determined the total fuel was 21.7; while the indicator displayed 20.3. Per maintenance procedure the total fuel quantity had to be put in manually. This is where we contacted Maintenance Control to determine where to put the actual fuel quantity. As this was happening I verified the previous write up and noticed the captain has indicated the quantity display indicators were blank. None of our indicators were blank leading me to believe the validity of the malfunction (inoperative display or inoperative fuel quantity indicator). We posed the question to maintenance; 'Could the indicators be working now?' Based on experience I have seen indicators go blank and come back. Their response was it is MEL'd therefore it is not working; regardless of the indication. At this point the fuel panel was indicating L C R 8.7 .9 10.4.This lead us to think if the indicators are accurate we have a 1700 lb imbalance. Our limitation is 1800 lbs thus nearing exceedance of our limitation compromising safety of flight. In order to mitigate any other fuel issues and misunderstanding and execute the flight safely; the captain requested the fuel from the left tank be transferred to the center to determine the accuracy of the fuel in the left tank. This would give us a new baseline to determine the accuracy of the fuel needed to be transferred to the left tank thus validating the accuracy or fault in the left indicator display. Indications before fuel transfer: L C R 8.7 .9  10.4 total 20.0.  After transfer: L C R  0  10  10.3; total 20.3. 10.7 was not transferred to the center tank; which validated our assumption of gauge/display accuracy. The desired fuel was moved from the center tank to the left in order to balance the fuel tank to bring it within lateral limits; meeting our limitations. During the balancing process we determined the method of manually inputting the fuel quantity into the FMC per MEL XX-XX-Y. In conclusion the maintenance derived fuel quantity of 10.7 in the left tank was not accurate; even while considering APU fuel burn of approximately 200 lbs per hour. In order to accomplish our flight in a safe manner we needed to positively determine the accuracy of the fuel quantity. We worked together with maintenance to identify and validate the fuel quantity of each tank as well as the total quantity before executing our flight. The flight was uneventful. A fuel log was notated on the flight plan. Accuracy of fuel is essential for safe flight.  Any time there is fuel quantity discrepancy; defuel all the tanks and start with a KNOWN baseline and fuel the tanks to determine the accuracy of the fuel system indications. Blindly accepting the previous maintenance procedure without quarrying the validity of the work can lead to dangerous conclusions. Therefore always approach each event/write up with an open and objective point of view. Flying is a dynamic and dangerous endeavor and both maintenance and flight crew need to agree to the airworthiness of the aircraft before flight.
[Report narrative contained no additional information.]
B757-200 flight crew reports being dispatched with multiple fuel quantity indication MELs and that the left gauge should have been blank but indicated 8.7; while maintenance had calculated 10.7. Suspecting an error in the calculations; fuel is transferred from the left tank to the center tank then a known quantity is transferred to the left tank; which agrees with the left tank gauge. A 1700 pound fuel imbalance had existed initially.