Narrative:

The purpose of this [report] is to draw attention to/document possible maintenance malpractice during ground operations for flight X; date; ZZZ to ZZZ1 on aircraft X. At approximately 20 minutes prior to block out we were informed by maintenance of fuel venting from our left wing in the vicinity of the '#1 surge tank' and that they would need to transfer some fuel to fix the issue. The maintenance representative (rep) began to transfer fuel from the #1 main tank (13.1 indicated qty; max 13.3) to the center wing tank (cw; ind 0.2) to try and reduce the pressure from the '#1 reserve' tank (actually #2 res; ind 3.9; max 4.0). After watching this unfold for a moment and overhearing the rep discussing the issue with someone on the phone; I asked why they were transferring from #1 main to the cw tank? The answer I received was somewhat surprising and disappointing... 'To reduce pressure from the fuel draining out of the #1 reserve'. I informed them that there was not a #1 reserve... The rep on the phone had no idea the aircraft was a 747-400 and said he thought it was a 747-8 which prompted some confusion for the local rep. I informed the rep that this aircraft is a 747-400 and there was no #1 reserve that it's a #2 reserve which drains into the #2 main tank; not the #1 main. Both the local rep/mechanic and the rep on the phone were surprised by this... After some discussion the next step they pondered caused additional concern... Their next idea was to transfer fuel from the #2/3 tanks to the #1/4 main tanks. I asked them to stop immediately and asked why we would do that? They seemed puzzled by the question. The answer we eventually got was that they planned to transfer 'two thousand' with the goal of relieving pressure in the #2 reserve so it would stop venting. I asked if he knew that the outboards couldn't hold that much. He had no idea what the capacity of the outboard tanks was; no idea that we couldn't just drain from the reserves (earlier discussion); didn't know the #2/3 mains were well below capacity (ind 22.3; max 38.1) already and in general; did not seem to understand how the fuel system on a 747-400 worked. In the meantime the fuel venting (caused apparently by a slight over servicing of a fuel tank combined with expansion due to warm temperatures) slowed and eventually stopped; as they also apparently had decided (after leaving the flight deck) to use the refueling panel on the wing to move fuel from the #2/3 main tanks to the cw tank (final cw qty = 8.9). Upon completion of this exercise the venting stopped; the fuel spill was cleaned up; I (the PIC) asked for a new wt/bal from the load master (cw indicating 8.9 vs 0.2 originally); we received the amended wt/bal; ran new performance and eventually blocked out 49 minutes late. After starting to push back I commanded the push be stopped as we determined there was a door open somewhere since the block out time was not indicated on the ACARS. I double checked the EICAS confirming there were no door messages. We then informed tow crew it might be a panel near the strut (per msg pulled from center CDU). They reset/reclosed the door and we subsequently departed for ZZZ1. The entire episode is very concerning as the mx reps seemed to be guessing at how the fuel system worked versus knowing how it worked. This could have resulted in a larger spill as well as a myriad of other issues. As a side note; after all was completed the local mechanic/mx rep was very apologetic; was trying hard to rectify/stop the leak and honestly very respectful throughout the process as he tried hard; but struggled to do the right thing due to being given incorrect inputs via telephone from another mx rep.I'm not a mechanic but it is unacceptable to have maintenance personnel working on the airplane who do not understand the systems. They must be appropriately trained or under supervision. This situation was unacceptable and does not inspire confidence in the capability/credibilityof the ZZZ maintenance personnel.

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Original NASA ASRS Text

Title: Captain reported misgivings after lack of knowledge caused a fuel spill during routine servicing.

Narrative: The purpose of this [report] is to draw attention to/document possible maintenance malpractice during ground operations for flight X; DATE; ZZZ to ZZZ1 on aircraft X. At approximately 20 minutes prior to block out we were informed by maintenance of fuel venting from our left wing in the vicinity of the '#1 surge tank' and that they would need to transfer some fuel to fix the issue. The maintenance representative (rep) began to transfer fuel from the #1 main tank (13.1 indicated qty; max 13.3) to the center wing tank (cw; ind 0.2) to try and reduce the pressure from the '#1 reserve' tank (actually #2 res; ind 3.9; max 4.0). After watching this unfold for a moment and overhearing the rep discussing the issue with someone on the phone; I asked why they were transferring from #1 main to the cw tank? The answer I received was somewhat surprising and disappointing... 'to reduce pressure from the fuel draining out of the #1 reserve'. I informed them that there was not a #1 reserve... The rep on the phone had no idea the aircraft was a 747-400 and said he thought it was a 747-8 which prompted some confusion for the local rep. I informed the rep that this aircraft is a 747-400 and there was no #1 reserve that it's a #2 reserve which drains into the #2 main tank; not the #1 main. Both the local rep/mechanic and the rep on the phone were surprised by this... after some discussion the next step they pondered caused additional concern... their next idea was to transfer fuel from the #2/3 tanks to the #1/4 main tanks. I asked them to stop immediately and asked why we would do that? They seemed puzzled by the question. The answer we eventually got was that they planned to transfer 'two thousand' with the goal of relieving pressure in the #2 reserve so it would stop venting. I asked if he knew that the outboards couldn't hold that much. He had no idea what the capacity of the outboard tanks was; no idea that we couldn't just drain from the reserves (earlier discussion); didn't know the #2/3 mains were well below capacity (Ind 22.3; max 38.1) already and in general; did not seem to understand how the fuel system on a 747-400 worked. In the meantime the fuel venting (caused apparently by a slight over servicing of a fuel tank combined with expansion due to warm temperatures) slowed and eventually stopped; as they also apparently had decided (after leaving the flight deck) to use the refueling panel on the wing to move fuel from the #2/3 main tanks to the cw tank (final cw qty = 8.9). Upon completion of this exercise the venting stopped; the fuel spill was cleaned up; I (the PIC) asked for a new wt/bal from the load master (cw indicating 8.9 vs 0.2 originally); we received the amended wt/bal; ran new performance and eventually blocked out 49 minutes late. After starting to push back I commanded the push be stopped as we determined there was a door open somewhere since the block out time was not indicated on the ACARS. I double checked the EICAS confirming there were no door messages. We then informed tow crew it might be a panel near the strut (per msg pulled from center CDU). They reset/reclosed the door and we subsequently departed for ZZZ1. The entire episode is very concerning as the mx reps seemed to be guessing at how the fuel system worked versus knowing how it worked. This could have resulted in a larger spill as well as a myriad of other issues. As a side note; after all was completed the local mechanic/Mx rep was very apologetic; was trying hard to rectify/stop the leak and honestly very respectful throughout the process as he tried hard; but struggled to do the right thing due to being given incorrect inputs via telephone from another mx rep.I'm not a mechanic but it is unacceptable to have maintenance personnel working on the airplane who do not understand the systems. They must be appropriately trained or under supervision. This situation was unacceptable and does not inspire confidence in the capability/credibilityof the ZZZ maintenance personnel.

Data retrieved from NASA's ASRS site 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.