Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Situational Awareness; Human-Machine Interface; Distraction; Confusion; Communication Breakdown; Workload
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Flight Crew Became Reoriented; General Maintenance Action
Aircraft; Human Factors; Procedure
The center tank fuel indicating system was on MEL and therefore an alternate fueling procedure was used to fuel the center tank to a known quantity. Just prior to Top Of Climb (TOC) my center tank fuel pump low pressure lights began to blink indicating the center tank was depleted of fuel. The center tank should not have been depleted of fuel yet and the low pressure lights should not have started blinking until TOC. This prompted my First Officer and I to question our fuel load that we thought we had and closely monitor our fuel burn.As stated above the Center Tank Fuel system was on MEL. While executing preflight duties Maintenance personnel came into the flight deck to verify our fuel load. Our fuel totalizer indicated that our fuel load was 19.1. Our departure ramp fuel load was supposed to be 21.4. However; the center tank indicating system was on MEL. No disrespect; but the Maintenance guy had a real 'deer in the headlights' look on his face and I could tell he was uncertain with this fueling procedure and what our fuel load really was. This prompted me to question him as our totalizer was indicating 19.1. He left the flight deck and came back shortly with the fueler. With the gallons added at that time; we determined that we had 21.3 on board. I asked the fueler to bump the fuel load to 21.4 or more considering APU burn. The Mechanic came back shortly thereafter and now appeared confident with the ME-10 form. The gallons added as indicated on the form led us to believe that we had a fuel total of 21.5; although our fuel totalizer still indicated 19.1. The jetway was pulled back and our load numbers arrived from Central Load Planning (CLP). The FMC was not allowing us to input our fuel load on the PERF-INIT page as per the MEL instructions. It was indicating 19.1 and our TOGW was under what it should have been; therefore impacting our takeoff data. I called Maintenance Control to query why we couldn't input the fuel amount into the he FMC. He did not have an answer but said that the airplane had been flying like this for the last 8 days and asked why we had a problem with it. We were day 9 of a 10 day MEL allowance. We then tried inputting our correct TOW into the FMC based off our fuel load of 21.5. The FMC accepted the corrected TOW and therefore updated our takeoff data which was my main concern at that point. Although my First Officer and I did not have an answer for why the FMC would not allow us to change the fuel load as per the MEL; but neither did Maintenance Control. We felt comfortable that our takeoff data was accurate with the updated TOW and our fuel load was supposed to be 21.5 by the gallons added as indicated on the ME-10 form. We continued with the flight and as stated earlier the center tank fuel indicating lights began to blink earlier than they should have; prompting me to once again question our center tank fuel load. We referenced MEL: 28-7D once again and both read it thoroughly; now that we had no other distractions. We replayed and talked about all the events that had taken place up to this point and started monitoring our fuel very closely. As the flight progressed we determined that our fuel totalizer was reading correctly based off the fuel in the main tanks and our fuel burn. We then determined that our departure fuel load was actually 19.1 and not 21.5 that we were led to believe we had. I notified Dispatch that I would be calling the Duty Officer once at our destination regarding our MEL: 28-7D. We continued to monitor our fuel closely and the destination weather. Initially the destination weather was overcast; but the marine layer burned off quickly and it became 'Clear' with visual approaches. As we passed a potential divert airport we determined that we had enough fuel to make it to our filed destination and based off the weather we expected no delays on our approach. I knew I had two options if unexpected ATC delays occurred by either declaring 'MIN FUEL' or declaring an emergency to expedite our approach phase to landing if needed. We had no delays on arrival; and on shutdown at the gate we ended up with 5.1 fuel on board which was approximately 2.4 less than we should have had. We determined that the gallons added on the ME-10 form were incorrect and off by approximately 350 gallons. I immediately called Dispatch and got transferred to the Duty Officer on duty. We discussed the events in order to come up with a solution to get proper and accurate fueling before we took this aircraft under this MEL. The Station Maintenance personnel really impressed me and instilled confidence with the steps that they took. They disabled the center tank and fuel totalizer which left us with main tank indication readings only. They then fueled the wing tanks full first. They next added a known quantity in the center tank so we knew our departure fuel load was accurate. With that being done; our FMC now performed the way it was suppose to as per the MEL. We had --- for the fuel load on the PERF-INIT page and were able to input our correct fuel load. We continued to our next destination and monitored our fuel as per the flight plan utilizing the 'Fuel Used' switch until the center tank was depleted. We briefed the outbound flight crew and the fueler as to how the previous Mechanics fueled the aircraft with main tanks first and how we monitored our enroute fuel.
[Report narrative contained no additional information.]
A B737-NG center tank fuel quantity totalizer was inoperative which required a special MEL procedure completion before the FMC PERF-INIT weight was correct. Maintenance failed to fully comply with complex procedure so the required fuel was 2;400 LBS low.