What was found
AFTER TAKEOFF FROM BWI, NR 1 HYDRAULIC QUANTITY FELL TO ZERO AND THE NR 1 ENGINE HYDRAULIC PUMP LIGHT ILLUMINATED. THE AIRCRAFT DIVERTED INTO MDT AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED AND FOUND O-RING CUT ON THE PRESSURE LINE. REMOVED AND REPLACED O-RING AND HYDRAULIC ENGINE DRIVEN PUMP IAW DHC PROCEDURES. COMPLIED WTH DHC HYDRAULIC LOSS CHECK IAW CHAPTER 05. A/C RETURNED TO SERVICE. (M)