What happened
During the cruise phase of flight, the flight crew observed a master caution light indicating a loss of pressure and fluid within the right hydraulic system. Following established checklists to troubleshoot the failure, the crew attempted to manually extend both the main and nose landing gear using the alternate extension control lever. While the main landing gear successfully extended and locked into position, the nose landing gear failed to extend.
As a result of the nose gear remaining in the retracted position, the aircraft was landed with the gear up.
The investigation
An initial inspection of the aircraft revealed that a B-nut connected to the check valve on the rudder power hydraulic shut-off valve had separated from the valve. This separation caused a total loss of both hydraulic quantity and pressure in the right system. An examination of the hydraulic tubing, including the check valve and the B-nut, showed no other abnormalities.
In the cockpit, investigators noted that the landing gear handle was in the stowed position. A placard on the alternate landing gear extension lever provided instructions to "Pull up forcibly Full Stroke." During subsequent maintenance, the aircraft was placed on jacks, where personnel successfully extended the nose landing gear. The alternate gear extension control system was inspected and no defects were found.