What was found
AIRCRAFT WAS GROUNDED: #1 ENGINE FUEL FILTER CLOG AFTER DEPARTURE PRIOR TO FL180. ECAM PROCEDU,RE STATED L TK PUMPS 1/2 OFF AND X FEED ON. LEFT TANK FUEL BECAM,E UNUSABLE AND BOTH LEFT AND RIGHT OUTER TANKS STOPPED TRANSFERR,ING TO MAIN TANKS WITH THE ONLY REMAINING USEABLE FUEL BEING THE, RIGHT MAIN TANK. DECESION MADE TO RETURN TO DSM, EMERGENCY DECLARED AIRCRAFT LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED THE #1 ENG. FUEL FILTER DIFFERENTIAL SWITCH IAW 73-11-10 AND 73-34-15.