What was found
ON A FLIGHT FROM RIC TO RDU WITH RDU IN SIGHT, HYDRAULIC PRESSURE WENT TO ZERO. GEAR WAS BLOWN DOWN. CHECK LIST FOLLOWED FOR A NO-HYDRAULIC PRESSURE LANDING. FLUID WAS EVIDENT IN NOSE WHEELWELL. MAINTENANCE TECHNICIANS DETERMINED ONLY PARTIAL LOSS OF FLUID AND PRESSURE ON SYSTEM 10 HOURS LATER. FOUND A B-NUT FOR NOSE GEAR-UP LINE LOOSE. TIGHTENED B-NUT. CYCLED GEAR, RAN ENGINES TO BLEED HYDRAULIC PUMPS. SYSTEM FUNCTIONED NORMALLY. SUSPECT CAUSE WAS A LOOSE JAM NUT AT BULKHEAD CONNECTION FROM WHEELWELL TO AVIONICS BAY ALLOWING FITTING TO VIBRATE LOOSE.