A B757 FLT CREW HAVE A FUEL IMBAL WHICH LEADS THEM TO BELIEVE THAT THEY MAY HAVE A FUEL LEAK OR BLOCKAGE. THEY DECIDE TO DIVERT TO HAVE THE ACFT LOOKED AT BY MAINT.

Narrative

NOTICED APPROX 1000 LBS FUEL IMBAL PASSING FL180. DECIDED TO WAIT UNTIL LEVELOFF TO ADDRESS ISSUE. UPON LEVEL AT FL370; NOTICED R TANK 3000 LBS HEAVIER THAN L. CHKED FUEL USED; TOTAL FUEL INDICATIONS ON FMC. AS BEST WE COULD TELL; OUR LEVELOFF FUEL INDICATED APPROX 3000 LBS LESS THAN PLANNED. CAPT REFERRED TO IRREGULAR PROC FOR FUEL CONFIGN LIGHT ILLUMINATED. DECIDED AGAINST ATTEMPTING TO BAL FUEL DUE TO UNCERTAINTY OF CAUSE OF IMBAL (IE; POSSIBLE FUEL LEAK IN L TANK). FUEL IN R TANK APPEARED TO BE STUCK AT '12.8.' VERIFIED R WING HVY BY HAND FLYING ACFT AND USING RUDDER TRIM TO LEVEL WINGS. TRIM REQUIRED INCREASED FROM 2.0 UNITS TO 4.0 UNITS AS FLT PROGRESSED DUE TO INCREASING IMBAL. UNABLE TO DETERMINE IF FUEL IN R WING WAS TRAPPED AND UNUSABLE. DECIDED TO DIVERT INTO LAX SINCE IT WAS ONLY 60 MI BEHIND US AND WX WAS CLR RATHER THAN CONTINUE TO DEN. DISPATCH AND MAINT CONCURRED WITH DIVERT DECISION SINCE FUEL STATE COULD NOT BE VERIFIED. REQUESTED AND RECEIVED PRIORITY HANDLING INTO LAX FOR UNEVENTFUL LNDG.