Fuel imbalance noted on approach. Landed outside imbalance limits.

Attributes
ACN	176239
Time
Date	199104
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : yul
State Reference	PQ
Altitude	msl bound lower : 3000 msl bound upper : 3000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tower : yul
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent : approach landing other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : second officer
Qualification	pilot : flight engineer
Experience	flight time last 90 days : 145 flight time total : 3200 flight time type : 145
ASRS Report	176239
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

While doing a descent to landing, it was noticed that the fuel in the #1 tank (left wing) was about 1700 pounds more than in the #3 (right wing) tank. This problem was noted at about 4000'. The limits for this aircraft is no more than 1000 pounds difference for landing. Before descent the fuel was balanced and during the flight xfeeding was never required. Fuel flows were noted to be the same on all engines. When the problem was noticed we started to xfeed from the #1 (heavy) tank. Just prior to landing, the fuel panel was configured for landing. But the fuel was still out of balance. The captain decided to continue the landing, since the aircraft showed no adverse flight characteristics of ctlability problems. I do not know the cause of the problem. I would suspect either a xfeed valve leaked fuel to another tank on descent, or some kind of a fuel leak. The problem was increased by my not catching the imbalance. Human factors: descent is always a busy time. This combined with being tired causes you to miss things that normally would not be missed. I was in bed at xa:00 pm the night before the flight, but could not fall asleep until xc:00 am. The xc:30 am alarm for a xf:00 am show time created a lack of sleep and fatigue that allowed the problem to get as far as it did. Callback conversation with reporter revealed the following information. Has received no information from the company as to the problem. Seemed reluctant to volunteer any information.

Original NASA ASRS Text

Title: FUEL IMBALANCE NOTED ON APCH. LANDED OUTSIDE IMBALANCE LIMITS.

Narrative: WHILE DOING A DSNT TO LNDG, IT WAS NOTICED THAT THE FUEL IN THE #1 TANK (L WING) WAS ABOUT 1700 LBS MORE THAN IN THE #3 (R WING) TANK. THIS PROB WAS NOTED AT ABOUT 4000'. THE LIMITS FOR THIS ACFT IS NO MORE THAN 1000 LBS DIFFERENCE FOR LNDG. BEFORE DSNT THE FUEL WAS BALANCED AND DURING THE FLT XFEEDING WAS NEVER REQUIRED. FUEL FLOWS WERE NOTED TO BE THE SAME ON ALL ENGS. WHEN THE PROB WAS NOTICED WE STARTED TO XFEED FROM THE #1 (HVY) TANK. JUST PRIOR TO LNDG, THE FUEL PANEL WAS CONFIGURED FOR LNDG. BUT THE FUEL WAS STILL OUT OF BALANCE. THE CAPT DECIDED TO CONTINUE THE LNDG, SINCE THE ACFT SHOWED NO ADVERSE FLT CHARACTERISTICS OF CTLABILITY PROBS. I DO NOT KNOW THE CAUSE OF THE PROB. I WOULD SUSPECT EITHER A XFEED VALVE LEAKED FUEL TO ANOTHER TANK ON DSNT, OR SOME KIND OF A FUEL LEAK. THE PROB WAS INCREASED BY MY NOT CATCHING THE IMBALANCE. HUMAN FACTORS: DSNT IS ALWAYS A BUSY TIME. THIS COMBINED WITH BEING TIRED CAUSES YOU TO MISS THINGS THAT NORMALLY WOULD NOT BE MISSED. I WAS IN BED AT XA:00 PM THE NIGHT BEFORE THE FLT, BUT COULD NOT FALL ASLEEP UNTIL XC:00 AM. THE XC:30 AM ALARM FOR A XF:00 AM SHOW TIME CREATED A LACK OF SLEEP AND FATIGUE THAT ALLOWED THE PROB TO GET AS FAR AS IT DID. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. HAS RECEIVED NO INFO FROM THE COMPANY AS TO THE PROB. SEEMED RELUCTANT TO VOLUNTEER ANY INFO.

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.