Narrative:

During flight planning; the release showed aircraft having MEL deferrals 28-4; center tank fuel pumps; and MEL 28-10d; fuel quantity densitometers. I searched but was unable to find any information in any source as to what the fuel quantity densitometers do or what the cockpit indication or effect I would need to be aware of while operating the airplane with one (or all) inoperative. Upon arrival at the airplane; I reviewed the logbook and discovered that the aircraft had been in the hangar for several days. The fuel onboard was over 48;000 pounds with over 19;000 pounds in the center tank (dispatch later reported that the aircraft had landed several days earlier with an arrival fuel of approximately 8000 pounds). Dispatch fuel was 29;500 pounds with MEL 28-4 restricting the center tank to no more than 5000 pounds. The center tank pumps had been placed on a placard (3 days earlier). A mechanic was in the cockpit balancing the wing tank fuel with the intent to de-fuel the excess fuel once the balance was complete. He had both center pumps on. I read the requirements of 28-4 which included the deactivation of the pumps by pulling and collaring the associated circuit breaker. When I first looked at the P6 panel; I found a large maintenance circuit breaker collar with a 'warning' tag attached - but it was not on a fuel pump circuit breaker. Instead; I discovered that the altitude slat power circuit breaker had been left collard. There was no entry in the logbook indicating work having been done on the slats. The de-fueling mechanic removed the circuit breaker collar/warning tag doing no review of the logbook or making no other inquiry as to why it was there in the first place. Since he was using the center pumps; I asked him if he had removed the pump circuit breaker collars in order to do so. He said the circuit breakers had not been collared. Again; the placard had been issued on (three days earlier). At this point; I asked for a supervisor so I could determine better precisely what work had been done on the airplane and to make certain that all MM requirements had in fact been accomplished. Supervisor arrived and listened to my report. He looked at the logbook and noted that the write-up on the center pumps stated that both pump low pressure lights illuminated with 2500 pounds showing on the center tank quantity indicator. He volunteered that the problem was probably not with the pumps but with the quantity indication and the placarding the pumps was simply the easiest way to deal with the problem. I asked why placard the pumps if they were not at fault; particularly when several MEL provisions allowed placarding various fuel quantity indication systems. At this point; he backed away from his initial statement and began to defend the placarding of the pumps. I looked farther back into the logbook and found a write-up describing the fuel quantity increasing from 48;000 to 51;000 pounds after fueling and decreasing back to 48;000 pounds when boost pumps were turned on. This suggested to me a fluctuation in the center tank indication (since at that fuel quantity; the wing tanks would be completely full at just over 15;500 pounds each and a 3000 pound increase in either wing tank would have created a fuel imbalance indication).I began to believe that the supervisor's initial observation may indeed have been correct (that the real problem was not with the pumps but with the indication system). I then reviewed the MEL restrictions for the various fuel quantity systems (28-10) and discovered that the restrictions were different from restrictions created by 28-4. Most significant was the 28-10b restriction on use of special reserve calculations. Our flight plan had been created using those reserve rules. The de-fueling process had finished and during that process the center boost pump low pressure lights came on with approximately 1500 pounds in the center tank. When no more fuel would transfer from the center tank; 800 pounds still showed on the gauge. Additionally; thoughthe wing tanks had been balanced prior to de-fueling; the left tank now showed 14;000 pounds while the right tanks showed 14;900 pounds leaving us below our dispatch release fuel. At this point; I questioned the placard more strongly and supervisor called for a manager. When the manager arrived; he listened to us both; reviewed the logbook and MEL provisions; then called maintenance control. In consultation with maintenance control; the manager was inclined toward my read of the situation; (though he had not yet come to a definitive position). He mentioned the change of the fuel quantity processor a week earlier and agreed that the problem seemed to be more of a quantity sensing issue than a pump issue when he said that we would probably had to take the airplane out of service; supervisor retorted that 'we don't need a new airplane; we just need a new crew.' I placed my observations of the fuel quantity indications during the de-fueling process in the logbook and refused the aircraft.

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Original NASA ASRS Text

Title: B757 Captain questioned MEL for center tank fuel pumps which he believed was actually a problem with fuel quantity gauges. When Maintenance cannot explain their reasoning to the reporter's satisfaction the aircraft was refused.

Narrative: During flight planning; the release showed aircraft having MEL deferrals 28-4; center tank fuel pumps; and MEL 28-10d; fuel quantity densitometers. I searched but was unable to find any information in any source as to what the fuel quantity densitometers do or what the cockpit indication or effect I would need to be aware of while operating the airplane with one (or all) inoperative. Upon arrival at the airplane; I reviewed the logbook and discovered that the aircraft had been in the hangar for several days. The fuel onboard was over 48;000 LBS with over 19;000 LBS in the center tank (Dispatch later reported that the aircraft had landed several days earlier with an arrival fuel of approximately 8000 LBS). Dispatch fuel was 29;500 LBS with MEL 28-4 restricting the center tank to no more than 5000 LBS. the center tank pumps had been placed on a placard (3 days earlier). A Mechanic was in the cockpit balancing the wing tank fuel with the intent to de-fuel the excess fuel once the balance was complete. He had both center pumps on. I read the requirements of 28-4 which included the deactivation of the pumps by pulling and collaring the associated circuit breaker. When I first looked at the P6 panel; I found a large maintenance circuit breaker collar with a 'warning' tag attached - but it was not on a fuel pump circuit breaker. Instead; I discovered that the ALT SLAT PWR circuit breaker had been left collard. There was no entry in the logbook indicating work having been done on the slats. The de-fueling Mechanic removed the circuit breaker collar/warning tag doing no review of the logbook or making no other inquiry as to why it was there in the first place. Since he was using the center pumps; I asked him if he had removed the pump circuit breaker collars in order to do so. He said the circuit breakers had not been collared. Again; the placard had been issued on (three days earlier). At this point; I asked for a Supervisor so I could determine better precisely what work had been done on the airplane and to make certain that all MM requirements had in fact been accomplished. Supervisor arrived and listened to my report. He looked at the logbook and noted that the write-up on the center pumps stated that both pump low pressure lights illuminated with 2500 LBS showing on the center tank quantity indicator. He volunteered that the problem was probably not with the pumps but with the quantity indication and the placarding the pumps was simply the easiest way to deal with the problem. I asked why placard the pumps if they were not at fault; particularly when several MEL provisions allowed placarding various fuel quantity indication systems. At this point; he backed away from his initial statement and began to defend the placarding of the pumps. I looked farther back into the logbook and found a write-up describing the fuel quantity increasing from 48;000 To 51;000 LBS after fueling and decreasing back to 48;000 LBS when boost pumps were turned on. This suggested to me a fluctuation in the center tank indication (since at that fuel quantity; the wing tanks would be completely full at just over 15;500 LBS each and a 3000 LB increase in either wing tank would have created a fuel imbalance indication).I began to believe that the Supervisor's initial observation may indeed have been correct (that the real problem was not with the pumps but with the indication system). I then reviewed the MEL restrictions for the various fuel quantity systems (28-10) and discovered that the restrictions were different from restrictions created by 28-4. Most significant was the 28-10b restriction on use of special reserve calculations. Our flight plan had been created using those reserve rules. The de-fueling process had finished and during that process the center boost pump low pressure lights came on with approximately 1500 LBS in the center tank. When no more fuel would transfer from the center tank; 800 pounds still showed on the gauge. Additionally; thoughthe wing tanks had been balanced prior to de-fueling; the left tank now showed 14;000 LBS while the right tanks showed 14;900 LBS leaving us below our dispatch release fuel. At this point; I questioned the placard more strongly and Supervisor called for a manager. When the Manager arrived; he listened to us both; reviewed the logbook and MEL provisions; then called Maintenance Control. In consultation with Maintenance Control; the Manager was inclined toward my read of the situation; (though he had not yet come to a definitive position). He mentioned the change of the fuel quantity processor a week earlier and agreed that the problem seemed to be more of a quantity sensing issue than a pump issue When he said that we would probably had to take the airplane out of service; Supervisor retorted that 'we don't need a new airplane; we just need a new crew.' I placed my observations of the fuel quantity indications during the de-fueling process in the logbook and refused the aircraft.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.