What was found
(CAN) AFTER COMPLETING A WATERDROP, BOTH WATERDOORS FAILED TO CLOSE AND LOCK. AC EXPERIENCED A COMPLETE HYDR FAILURE CAUSED BY FAILURE OF ONE-WAY CHECK VALVE IN MAIN PRESSURE LINE AT WING STA 54 ON RT WING LE. THIS CHECK VALVE'S PURPOSE IS TO STOP HYD PRESSURE FLOWING BACK TO ENG DRIVEN PUMP WHEN USING GROUND TEST EQUIPMENT, AUXILARY HYD PUMP. AC PERFORMED EMERGENCY LANDING GEAR EXTENSION, RETURNED TO BASE, LANDED SAFELY. CHECK VALVE HSG IS CONSTRUCTED OF ALUMINUM. AFTER RECEIVING REPORTS OF FAILURE OF THIS CHECK VALVE, MFG PRODUCED SB 215-0466(STAINLESS STEEL CHECK VALVES)TO RECTIFY THIS PROBLEM. OUR ORGANIZATION WILL EMBODY THIS SB. ORDERED THESE CHECK VALVES(2 PER AC) TO BE INSTALLED. (TC NR 20060427007)