Narrative:

Shortly after level off at cruise second officer advised that we were experiencing 'fuel problems' -- fuel quantity #2 tank decreasing, fuel quantity in auxiliary tank increasing. I observed how rapid these quantity changes were taking place. Thereafter requested clearance back to phl requesting clearance to 25000' and called for inadvertent transfer of fuel checklist. After initial contact with phl tower they advised 'we have declared emergency for you' equipment will follow you down the runway'. After landing requested equipment check aircraft for possible fuel leak. They advised aircraft had a substantial fuel leak. Shut aircraft down and deplaned passenger thru rear airstair as precautionary measure! After passenger were bussed to terminal and company maintenance arrived, we inspected aircraft. Observed fuel draining from aft fuel drain mast, fuel leaking in and around wheel well. Opened aft cargo bin observed substantial amounts of fuel standing in cargo bin. We diagnosed problem as inadvertent transfer of fuel and reacted accordingly -- checklist, etc. Landed without further event. Passenger deplaned in orderly manner. Company responded well with ground support. Maintenance later advised that we had experienced check valve failure and that auxiliary tank had a crack in it! I reflect back on this potentially serious problem to recall some things I might have done differently! My first officer was new in the right seat. My F/east was new on equipment relatively 6 months. We had been just terminated from radar environment and instructed to contact ny arinc for our overwater portion. I found myself more concerned with the message he was conveying to ATC in reference to our situation and the second officer's actions being taken at time, that I didn't really think the problem all the way thru what could cause inadvertent transfer of fuel besides bad check valves. Maybe a fuel leak, tank lines, etc, but both at same time? Complacency maybe, but we couldn't be sure. No fumes or smell in cabin. Maybe a more thorough investigation thru cabin windows, etc. Could a system (warning system) be devised that would indicate to crew that there is fuel leaking in cargo bin? Maybe I should have declared an emergency! Callback conversation with reporter revealed the following: reporter added more information that had been left out of original text. During the return to land when the fuel transfer checklist was being accomplished, the second officer noted that fuel was draining from the wingtip vents and therefore they knew it was coming from the auxiliary tank, because of fuel system set up. They had no idea of the leak within the auxiliary fuel tank but suspected something was very wrong when they attempted to use the fuel that was in the auxiliary fuel tank which had been empty on departure. They could not pressurize the auxiliary fuel tank and then had an idea that its structural integrity had been compromised. Reporter states that an 18' split was found in the auxiliary tank, created by the vent lines being ripped out of the cell thereby puncturing or ripping the casing. Maintenance later found and pumped out 235 gals of fuel from the aft cargo bin. The aircraft was scheduled into a 'B' check which is a comprehensive inspection. Reporter does not know if the other 16 aircraft of this type model are going to be checked or not. He stated that this situation could have existed for some time as the tanks are not always services with fuel.

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Original NASA ASRS Text

Title: LGT ACR ACFT RETURNS TO LAND WHEN FLT CREW DETECTS AN INADVERTENT TRANSFER OF FUEL OCCURRING.

Narrative: SHORTLY AFTER LEVEL OFF AT CRUISE S/O ADVISED THAT WE WERE EXPERIENCING 'FUEL PROBLEMS' -- FUEL QUANTITY #2 TANK DECREASING, FUEL QUANTITY IN AUX TANK INCREASING. I OBSERVED HOW RAPID THESE QUANTITY CHANGES WERE TAKING PLACE. THEREAFTER REQUESTED CLRNC BACK TO PHL REQUESTING CLRNC TO 25000' AND CALLED FOR INADVERTENT TRANSFER OF FUEL CHECKLIST. AFTER INITIAL CONTACT WITH PHL TWR THEY ADVISED 'WE HAVE DECLARED EMER FOR YOU' EQUIPMENT WILL FOLLOW YOU DOWN THE RWY'. AFTER LNDG REQUESTED EQUIPMENT CHECK ACFT FOR POSSIBLE FUEL LEAK. THEY ADVISED ACFT HAD A SUBSTANTIAL FUEL LEAK. SHUT ACFT DOWN AND DEPLANED PAX THRU REAR AIRSTAIR AS PRECAUTIONARY MEASURE! AFTER PAX WERE BUSSED TO TERMINAL AND COMPANY MAINT ARRIVED, WE INSPECTED ACFT. OBSERVED FUEL DRAINING FROM AFT FUEL DRAIN MAST, FUEL LEAKING IN AND AROUND WHEEL WELL. OPENED AFT CARGO BIN OBSERVED SUBSTANTIAL AMOUNTS OF FUEL STANDING IN CARGO BIN. WE DIAGNOSED PROBLEM AS INADVERTENT TRANSFER OF FUEL AND REACTED ACCORDINGLY -- CHECKLIST, ETC. LANDED WITHOUT FURTHER EVENT. PAX DEPLANED IN ORDERLY MANNER. COMPANY RESPONDED WELL WITH GND SUPPORT. MAINT LATER ADVISED THAT WE HAD EXPERIENCED CHECK VALVE FAILURE AND THAT AUX TANK HAD A CRACK IN IT! I REFLECT BACK ON THIS POTENTIALLY SERIOUS PROBLEM TO RECALL SOME THINGS I MIGHT HAVE DONE DIFFERENTLY! MY F/O WAS NEW IN THE RIGHT SEAT. MY F/E WAS NEW ON EQUIPMENT RELATIVELY 6 MONTHS. WE HAD BEEN JUST TERMINATED FROM RADAR ENVIRONMENT AND INSTRUCTED TO CONTACT NY ARINC FOR OUR OVERWATER PORTION. I FOUND MYSELF MORE CONCERNED WITH THE MESSAGE HE WAS CONVEYING TO ATC IN REFERENCE TO OUR SITUATION AND THE S/O'S ACTIONS BEING TAKEN AT TIME, THAT I DIDN'T REALLY THINK THE PROBLEM ALL THE WAY THRU WHAT COULD CAUSE INADVERTENT TRANSFER OF FUEL BESIDES BAD CHECK VALVES. MAYBE A FUEL LEAK, TANK LINES, ETC, BUT BOTH AT SAME TIME? COMPLACENCY MAYBE, BUT WE COULDN'T BE SURE. NO FUMES OR SMELL IN CABIN. MAYBE A MORE THOROUGH INVESTIGATION THRU CABIN WINDOWS, ETC. COULD A SYSTEM (WARNING SYSTEM) BE DEVISED THAT WOULD INDICATE TO CREW THAT THERE IS FUEL LEAKING IN CARGO BIN? MAYBE I SHOULD HAVE DECLARED AN EMER! CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: REPORTER ADDED MORE INFO THAT HAD BEEN LEFT OUT OF ORIGINAL TEXT. DURING THE RETURN TO LAND WHEN THE FUEL TRANSFER CHECKLIST WAS BEING ACCOMPLISHED, THE S/O NOTED THAT FUEL WAS DRAINING FROM THE WINGTIP VENTS AND THEREFORE THEY KNEW IT WAS COMING FROM THE AUX TANK, BECAUSE OF FUEL SYSTEM SET UP. THEY HAD NO IDEA OF THE LEAK WITHIN THE AUX FUEL TANK BUT SUSPECTED SOMETHING WAS VERY WRONG WHEN THEY ATTEMPTED TO USE THE FUEL THAT WAS IN THE AUX FUEL TANK WHICH HAD BEEN EMPTY ON DEP. THEY COULD NOT PRESSURIZE THE AUX FUEL TANK AND THEN HAD AN IDEA THAT ITS STRUCTURAL INTEGRITY HAD BEEN COMPROMISED. REPORTER STATES THAT AN 18' SPLIT WAS FOUND IN THE AUX TANK, CREATED BY THE VENT LINES BEING RIPPED OUT OF THE CELL THEREBY PUNCTURING OR RIPPING THE CASING. MAINT LATER FOUND AND PUMPED OUT 235 GALS OF FUEL FROM THE AFT CARGO BIN. THE ACFT WAS SCHEDULED INTO A 'B' CHECK WHICH IS A COMPREHENSIVE INSPECTION. REPORTER DOES NOT KNOW IF THE OTHER 16 ACFT OF THIS TYPE MODEL ARE GOING TO BE CHECKED OR NOT. HE STATED THAT THIS SITUATION COULD HAVE EXISTED FOR SOME TIME AS THE TANKS ARE NOT ALWAYS SERVICES WITH FUEL.

Data retrieved from NASA's ASRS site as of July 2007 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.