What was found
AIRCRAFT WAS GROUNDED: YELLOW HYDRAULIC SYSTEM RESERVOIR LOW LEVEL ECAM MESSAGE AT CRUISE. CREW ACCOMPLISHED ECAM PROCEDURES. AN EMERGENCY WAS DECLARED AND THE AIRCRAFT LANDED AT PHL SAFELY WITHOUT FURTHER INCIDENT. MAINTENANCE FOUND FAULTY / LEAKING UNION PACKING ON YELLOW HYDRAULIC SYSTEM ELECTRIC PUMP HIGH PRESSURE MANIFOLD CHECK VALVE AND REPLACED IT PER AMM 29-24-21.A SATISFACTORY LEAK / OPERATIONAL CHECK WAS ACCOMPLISHED.