2022-06 · NASA ASRS report 1906320
Flight crew reported a fuel imbalance in flight which resulted from incorrectly following MEL instructions.
Dispatched with #2 Tank Fuel Quantity Indication Inop. (MEL-XX-XX-XX-XX) At FL110 descending into ZZZZ received a Level Two TANK 1 Fuel QTY LO alert.The tank one quantity indicated 4;000 lbs and tank three indicated 4;200 lbs. Referring to the QRH alert conferred that the quantities were valid even though the fuel burned thus far indicated a total fuel amount on board of about the planned FOD of about 20;300 lbs.As a result of the QRH consultation a [request for priority handling] due to the alert and with ATC priority handling an uneventful landing was performed. The fuel uploaded at ZZZZ1 was a total of 127;000 lbs.I reviewed the Fuel Manual Procedures and based on the total amount determined this was an even split (by three) tank to engine quantity situation and there were no normal checklist manual procedures to be performed other than fuel pumps on before start and off after shutdown.I was incorrect #1-36.7 #2-53.5 #3-36.7 was the load in ZZZZ1 (not equal quantities)As we checked the fuel quantity enroute we referenced the UFOB amount on the MCDU Progress page and every check indicated an above amount compared to the FPLAN.A possible rewrite of the MEL to alert the pilots to a possible unequal tank load and the greater need to attention of the pilots and Maintenance efforts to transfer fuel on the ground to rectify the unequal amounts before takeoff.EFOB at shutdown was 20;500 lbs.#1-2;900#2-XXX--14;600 Estimated#3-3;000
While on approach into ZZZZ we received a Level 1 TNK3 FUEL QTY LOW alert. I ran the QRH checklist from the jump seat which states that the fuel quantity in tank 3 inboard compartment is less than 3;500 lbs. When we switched back to the fuel synoptic I noted that the fuel in tank 3 was 3;200 lbs. and fuel in tank 1 was more; I think 4;000 lbs. at that time. I did a quick fuel calculation based on fuel burned and total fuel we started with and determined that our total fuel was over 21;000 lbs. The NOTE in the QRH says that the alert is based on a mechanical float switch and should be considered valid. I showed this to the Captain (who was PM (Pilot Monitoring)) and told him I thought it was an accurate alert and we had less than 3;500 lbs. in tank 3. He [requested priority handling] for possible low fuel state to ensure we received landing priority. The fuel in tanks 1 and 3 continued to decrease as would be expected and we landed with approximately 2;700 lbs. in tank 1 and 3;700 lbs. in tank 1. One of the important factors in the situation is that we were operating with an MEL for the #2 Main Tank Fuel Quantity Indication Inoperative. This MEL requires several steps which we followed; however when I did the required fuel checks in flight I did not check the fuel in each tank individually against the fuel burned from each tank individually. I totaled the fuel burned and compared it to our initial fuel. The MEL (now that I have re-read it) directs us to compute each tank individually. Had I done this I would have realized we did not distribute fuel from the #2 tank (which had more fuel than #1 and #3 at takeoff) to tanks #1 and #3; and the problem would have been averted.The cause was crew induced by not properly transferring fuel from the #2 tank to tanks 1 and 3; and by not following the MEL steps properly to check fuel in each individual tank during the fuel checks. In my opinion the MEL; flying without a fuel totalizer and main tank fuel indication; sets up crews (and sometimes Maintenance) for failure because the issue of a missed step like in this case is not obvious until later in flight. If we continue to fly with this MEL I would suggest an emphasis on the need to ensure the tanks are balanced during the after takeoff checklist or upon reaching cruise FL.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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