A300-600 SUFFERS LOSS OF FUEL COMPUTER; THUS NEGATING FUEL MANAGEMENT. FLT CREW DECLARES EMERGENCY AND RETURNS TO LAND OVERWT AT DEP ARPT.

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AFTER TKOF CLBING THROUGH APPROX 2000 FT WITH SLATS JUST RETRACTED; THE TRIM TANK SYS FAULT MESSAGE CAME ON. WE TRIED CYCLING THE SLATS AND CYCLING THE L AND R INNER FUEL TANK PUMPS FOR THE AUTO FUEL FEED LOGIC; NEITHER WORKED. WE FOLLOWED THE ECAM MESSAGE TO TURN OFF THE TRIM TANK PUMP SWITCHES AND THE TRIM TANK MODE FORWARD. THE NEXT PROB WHILE WE WERE CONTINUING OUR CLB WAS; WE LOST ALL FUEL INDICATIONS AND QUANTITIES. FUEL PAGE WENT TO ALL XXX'S ON QUANTITIES; PUMPS WENT AMBER AND ALL FUEL LINES TO EVERY TANK WAS ALSO AMBER. THE L SCREEN CTR OF GRAVITY XX'S GROSS WT XX'S AND THE FUEL TOTAL WENT XXXX'S. THE OVERHEAD FUEL QUANTITY INDICATORS WENT BLACK/BLANK. WE HAD NO INDICATION OF WHICH TANKS/TANK WAS FEEDING THE ENGS. I IMMEDIATELY WENT FUEL XFEED. WE WERE STILL CLBING SO I REQUESTED TO LEVEL AT FL250; WE WERE CLBING THROUGH IT AND NOW DSNDING BACK DOWN TO FL250. THERE IS NO PROC FOR LOSS OF FUEL QUANTITY INDICATION. WE NOW COULD ONLY ASSUME WE HAD WING TANK FUEL GRAVITY FEEDING. I ALSO CHKED OUR FUEL BURN ON THE ENG GAUGES WHICH WAS 11000 LBS PER HR. WE WERE AIRBORNE 25 MINS. THAT GAVE US APPROX 1 HR OF FLT TIME. I WAS USING THE 16000 LBS WE HAD IN OUR WINGS AS ALL THE FUEL WE HAD. WE ASKED TO RETURN TO ZZZ FOR A LNDG AND DECLARED AN EMER/PAN TO ATC. THIS WAS DECLARED BECAUSE I KNEW WE WERE GOING TO BE OVERWT FOR LNDG; OUR TKOF WT WAS 375000 LBS. WE ALSO ASKED CFR TO ROLL OUT FOR POSSIBLE HOT BRAKES. THE DSCNT AND APCH WAS COMPLETED ALONG WITH TELLING THE FLT ATTENDANTS AND PAX OF OUR SITUATION. THE TOUCHDOWN WAS VERY SMOOTH WITH A DSCNT RATE OF 200 FT OR LESS; AIRSPD 153 KTS AND FOUND OUT LATER THE WT WAS APPROX 365000 LBS. BRAKES WERE SET TO MEDIUM AND THE TEMPS REACHED A MAX OF 355 DEGS. OUR FLT ATTENDANT #1 DID AN EXCELLENT JOB OF REVIEWING HER PROCS IF AN EVAC WERE NECESSARY AND INFORMED THE OTHER FLT ATTENDANT. THE LNDG TAXI BACK WAS UNEVENTFUL WITH THE CFR FOLLOWING. THE FLT ATTENDANTS HELPED THE PAX DEPLANE AT A HARD STAND AND THE CREW GET BACK INTO THE COUNTRY. MAINT FOUND THE FUEL QUANTITY COMPUTER BAD AND NEEDED REPLACED.