What was found
(CAN) A/C ON ROUTINE FLT ON APPROACH PLANNED FLAPS FOR LDG & SELECTED FLAPS ON SCHEDULE. AFTER FLT CREW SELECTED FLAP TO 25 DEGS, MASTER CAUTION HYDRAULIC WARNING LIGHT FLASHED. AT TIME CREW NOTICED 'A' SYS HYDRAULIC QUANTITY READING ZERO - HYDRAULIC PRESSURE HELD STEADY AT 300 PSI. CREW ELECTED TO LAND A/C WITH FLAPS AT 25 - LDG UNEVENTFUL.MAINT INSP FOUND HYDRAULIC LEAK IN LT MLG WHEEL WELL- MLG MANUAL ISOLATION VALVE. MAINT REPLACED VALVE, & REPLENISHED SYS 'A' HYDRAULICS. LEAK CHECK PERFORMED AS PER MM 32-32-111 & MAINT FOUND NR 1 ENGINE DRIVEN PUMP HAD NO PRESSURE: MAINT REPLACED PUMP,&CARRIEDOUT LEAK CHECK AS PER MM 29-11-31, NO FAULT