What was found
(CAN) AFTER START OF THE NR 1 ENGINE, THE HYDRAULIC PUMP CAUTION LIGHT REMAINED ON WITH ZERO PRESSURE INDICATED ON THE ASSOCIATED HYDRAULIC SYSTEM PRESSURE GAUGE. AIRCRAFT ENGINES WERE SUBSEQUENTLY SHUTDOWN AND ENGINEERING CONTACTED TO CONDUCT DEFECT RECTIFICATION PRIOR TO RETURNING THE AIRCRAFT TO SERVICE. ENGINEERING DEFECT INVESTIGATION REVEALED THAT THE NR 1 ENGINE DRIVEN HYDRAULIC PUMP DRIVE SHAFT WAS SHEARED. THE HYDRAULIC PUMP WAS REPLACED WITH A SERVICEABLE ASSY IAW AMM 29-10-11 AND THE AIRCRAFT SUBSEQUENTLY RETURNED TO SERVICE. (TC NR 20070312001)