What was found
(CAN) AFTER SUCCESSFUL GROUND TEST OF ACCUMULATORS AT 70 PERCENT NG, AND ENGINE BROUGHT UP TO FLIGHT IDLE, HORN AND LOW HYDRAULIC PRESSURE LIGHT ILLUMINATED AND LOSS BOOSTED CONTROL WAS NOTED BY FLIGHT CREW. ACFT SHUTDOWN. SUBSEQUENT INSPECTION FOUND HYD PUMP UNABLE TO PRODUCE PRESSURE. UPON DISMANTLING PUMP, DRIVE GEAR HAD SEPARATED FROM SHAFT, WITH 2 BROKEN TEETH AND DRIVEN GEAR HAD 1 BROKEN TOOTH. ALL 3 GEARS FOUND IN PUMP AND NO OTHER EVIDENCE OF DAMAGE NOTED. NO CONTAMINATION FOUND ON CHIP DETECTOR, SCREEN OR FILTER. HYD FLUID FLUSHED CLEANED FILTER AND REPLACED HYDRAULIC PUMP WITH SERVICEABLE PUMP. THERE HAD BEEN NO PRIOR INDICATOR OF IMPENDING FAILURE OF THE PUMP. NO FURTHER PROBLEM FOUND POST RUN AND SUCCESSFUL TEST FLIGHT.