What was found
BOS - FLT 4420 - DURING APPROACH TO BOS, THE CREW REPORTED THE LOSS OF HYDRAULIC QUANTITY AND PRESSURE. A MISSED APPROACH WAS PERFORMED AND CREW ESTABLISHED THAT GEAR WAS DOWN AND LOCKED. AIRCRAFT LANDED AND TAXIED TO THE GATE WITHOUT INCIDENT. MAINTENANCE FOUND HYDRAULIC PRESSURE/QUANTITY INDICATOR CIRCUIT BREAKER OPEN. BREAKER WAS RE-SET AND SYSTEM INDICATED NORMAL. (X)