Narrative:

On ground at destination airport, fuelers discovered a 9000 pound lateral fuel imbal. Crew, after thorough discussion, can conclude no reason for the imbal. There is a strong possibility that the imbal occurred during the flight, although the aircraft was hand flown for approach and landing with no abnormal trim or control inputs. My concern is with warning system. We now have a procedure in which center tank fuel pumps are prohibited from being turned on with less than 5000 pounds of fuel in center tanks. We have a warning system which causes a 'fuel confign' light to illuminate for 3 reasons: 1) more than 1200 pounds in center tank and no center tank pumps on, 2) a lateral fuel imbal (1500-2500 pounds), and 3) low fuel. Normally, when the fuel confign light illuminates showing more than 1200 pounds and no pumps, it is canceled and a subsequent imbal will cause a re-illumination of the light. In this case, we had 1200 pounds of fuel in center tank, and the variance in quantity, caused presumably by sloshing, to jut above and just below 1200 pounds -- repeatedly -- caused several repeated illuminations of the warning light with the result that we eventually ignored the light. If the fuel imbal did occur while airborne, I feel that a contributing factor in our failure to detect the imbal was the fact that the fuel confign warning light was rendered useless by the repeated warnings caused by having 1200 pounds of fuel in the center tank. As this situation occurs fairly frequently --that of flying with approximately 1200 pounds in the center tank -- perhaps a warning should be issued that the imbal and low fuel functions of the system will not be of use when it occurs. Callback conversation with reporter revealed the following information: the reporter stated the aircraft was a B767-200 and fuel will migrate into the center tank in-flight and raise the fuel level above 1200 pounds, triggering the 'fuel confign' light. The reporter said this continuous resetting of the warning leads to ignoring the light. Callback conversation with reporter acn 434158 revealed the following information: the reporter stated any action by the air carrier with the FAA and the manufacturer for some corrective action is unknown. The reporter said the fuel in the center tank and prohibition of boost pump operation with less than 5000 pounds in the tank is an airworthiness directive and limits any changes.

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Original NASA ASRS Text

Title: A B767-200 ON ARR A FUELER DISCOVERED A 9000 LB FUEL IMBAL NOT NOTED BY THE FLC DURING THE FLT BUT WHO RECALL HAVING TO RESET THE 'FUEL CONFIGN' WARNINGS SEVERAL TIMES.

Narrative: ON GND AT DEST ARPT, FUELERS DISCOVERED A 9000 LB LATERAL FUEL IMBAL. CREW, AFTER THOROUGH DISCUSSION, CAN CONCLUDE NO REASON FOR THE IMBAL. THERE IS A STRONG POSSIBILITY THAT THE IMBAL OCCURRED DURING THE FLT, ALTHOUGH THE ACFT WAS HAND FLOWN FOR APCH AND LNDG WITH NO ABNORMAL TRIM OR CTL INPUTS. MY CONCERN IS WITH WARNING SYS. WE NOW HAVE A PROC IN WHICH CTR TANK FUEL PUMPS ARE PROHIBITED FROM BEING TURNED ON WITH LESS THAN 5000 LBS OF FUEL IN CTR TANKS. WE HAVE A WARNING SYS WHICH CAUSES A 'FUEL CONFIGN' LIGHT TO ILLUMINATE FOR 3 REASONS: 1) MORE THAN 1200 LBS IN CTR TANK AND NO CTR TANK PUMPS ON, 2) A LATERAL FUEL IMBAL (1500-2500 LBS), AND 3) LOW FUEL. NORMALLY, WHEN THE FUEL CONFIGN LIGHT ILLUMINATES SHOWING MORE THAN 1200 LBS AND NO PUMPS, IT IS CANCELED AND A SUBSEQUENT IMBAL WILL CAUSE A RE-ILLUMINATION OF THE LIGHT. IN THIS CASE, WE HAD 1200 LBS OF FUEL IN CTR TANK, AND THE VARIANCE IN QUANTITY, CAUSED PRESUMABLY BY SLOSHING, TO JUT ABOVE AND JUST BELOW 1200 LBS -- REPEATEDLY -- CAUSED SEVERAL REPEATED ILLUMINATIONS OF THE WARNING LIGHT WITH THE RESULT THAT WE EVENTUALLY IGNORED THE LIGHT. IF THE FUEL IMBAL DID OCCUR WHILE AIRBORNE, I FEEL THAT A CONTRIBUTING FACTOR IN OUR FAILURE TO DETECT THE IMBAL WAS THE FACT THAT THE FUEL CONFIGN WARNING LIGHT WAS RENDERED USELESS BY THE REPEATED WARNINGS CAUSED BY HAVING 1200 LBS OF FUEL IN THE CTR TANK. AS THIS SIT OCCURS FAIRLY FREQUENTLY --THAT OF FLYING WITH APPROX 1200 LBS IN THE CTR TANK -- PERHAPS A WARNING SHOULD BE ISSUED THAT THE IMBAL AND LOW FUEL FUNCTIONS OF THE SYS WILL NOT BE OF USE WHEN IT OCCURS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACFT WAS A B767-200 AND FUEL WILL MIGRATE INTO THE CTR TANK INFLT AND RAISE THE FUEL LEVEL ABOVE 1200 LBS, TRIGGERING THE 'FUEL CONFIGN' LIGHT. THE RPTR SAID THIS CONTINUOUS RESETTING OF THE WARNING LEADS TO IGNORING THE LIGHT. CALLBACK CONVERSATION WITH RPTR ACN 434158 REVEALED THE FOLLOWING INFO: THE RPTR STATED ANY ACTION BY THE ACR WITH THE FAA AND THE MANUFACTURER FOR SOME CORRECTIVE ACTION IS UNKNOWN. THE RPTR SAID THE FUEL IN THE CTR TANK AND PROHIBITION OF BOOST PUMP OP WITH LESS THAN 5000 LBS IN THE TANK IS AN AIRWORTHINESS DIRECTIVE AND LIMITS ANY CHANGES.

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.