Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 180; Flight Crew Total 8000; Flight Crew Type 4000
Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural MEL / CDL; Inflight Event / Encounter Fuel Issue
General None Reported / Taken
Aircraft; Human Factors
MEL'd center tank pumps. Captain and I both reviewed the MEL. Big item is maintenance verifying that no fuel was added. Flight planned with 10.7 gate fuel and 10.4 takeoff fuel. Burn 4.3. FAR 3.7. Planned remaining fuel 6.1. 0 unusable. MEL for center tank pumps has maintenance verify that no fuel was added which maintenance did. Fuel in center tank at the time was 2.9. It didn't register at that point with either myself or the Captain that our flight plan didn't match what was in the center tank. Since the plane arrived with 2.9 unusable and maintenance had verified no change I suppose we assumed that the fuel plan sheet was correct when in reality it showed zero unusable fuel. I remember seeing the zero unusable on the plan and then checking that we has the required fuel on board from looking at the totalizer and comparing gate fuel. We taxied out and took off. As I pulled the gear up I looked at the fuel again as a normal cross check and did some mental math that didn't quite make sense and that's when it sunk in that our center tank was unusable fuel and hadn't been considered when briefing the fuel load vs. our dispatch release. We took off with 10.4; minus the 2.9 indicated unusable = 7.5 usable. I pointed this out to the captain and suggested we return to [departure airport]. At this point we were climbing through approximately 2;500 feet. The Captain said he wanted to talk to Dispatch so I took the plane and radios while he spoke with Dispatch. After talking to Dispatch they (Captain and Dispatch) decided to declare minimum fuel and continue to our destination. I still believe a return to [departure airport] was the safest course of action but my advocacy proved ineffective. I was confident we could make our destination and land; but I was not confident that we weren't going to have an emergency [state] to do it. At the time the decision to continue was made we showed landing with 7.4 on the FMC; minus the 2.9 unusable = 4.5 which was above our required FAR reserve of 3.7. As the flight progressed; landing fuel decreased on the FMC to a low of 6.4; but so did the amount indicated in the center tank so the calculation of FMC landing fuel; unusable never put us below FAR. Perhaps the jet (scavenge) pumps were active and some of the fuel actually got burned? My systems knowledge says that shouldn't have happened; but it seems to have. We also had an imbalance of 500 LBS high on the left wing tank by the time we reached TOD (which we fixed by crossfeed) which would also indicate that some of the center tank fuel was actually burned (thankfully). When we landed the center tanks had 2.17 remaining. The left tank had 2.1 and the right tank had 2.1 so we actually landed with 4.2 usable (at the gate after a 5+ minute taxi).
B737 FO reported they took off without complying with a fuel system MEL and were left with less fuel than they were planned with.