What was found
AIRCRAFT RETURNED FROM FLIGHT AND DECLARED EMERGENCY DUE TO " HYDRAULIC QUANTITY CAS MESSAGE", COMBINED HYDRAULIC SYSTEM INDICATION WAS IN RED. MAINTENANCE NOTED THE “INDICATION (HYDRAULIC QUANTITY TRANSMITTER)”. AIRCRAFT INSPECTION WAS PERFORMED FOR POSSIBLE HYDRAULIC LEAK, NIL FOUND. APPLIED MEL 29-08-01 CATEGORY "C" FOR COMBINED HYDRAULIC SYSTEM QUANTITY INDICATION (EICAS) AND APPLIED MEL 29-06-01 CATEGORY "C" FOR COMBINED HYDRAULIC SYSTEM QUANTITY GAUGE (FUSELAGE). MAINTENANCE ACTIONS TO BE ACCOMPLISHED PRIOR TO EACH AIRCRAFT DEPARTURE. MAINTENANCE REMOVED AND REPLACED COMBINED HYDRAULIC QUANTITY TRANSMITTER IAW AMM 29-33-03, PERFORMED SYSTEM OPERATIONAL CHECK AND RESULT WAS SATISFACTORY.