What was found
JUST AFTER LEVEL OFF AT 16000 EXPERIENCED COMPLETE SYS-A HYD FAILURE. QTY AND PRESSURE BOTH WENT IMMEDIATELY TO ZERO. RAN QRH CHECKLIST, TIMED SYS-A FLUID SHUTOFF SWITCHES OFF FOR 55 MIN TO LANDING. LED NR 5 AMBER AND GREEN LIGHTS ON, ALL SLATS AND LED LIGHTS WERE GREEN. WHILE TROUBLESHOOTING HYDRAULIC LEAK IN LT W/W FOUND O-RING ON HYDRAULIC FLOW VALVE ON AFT BULKHEAD LEAKING. REMOVED AND REPLACED O-RING ON HYD VALVE PER 27-100 SMP.