Incident Sequence
Following takeoff, both main landing gears extended and locked, but the nose gear remained in an in-transit position. Attempts to secure the nose gear were unsuccessful. During the landing roll, the nose gear collapsed.
Hydraulic System Findings
The emergency hand pump could not generate pressure in the secondary system due to leakage past the shuttle valve and the shuttle bore in the end cap of the left gear actuator. Excessive clearance was noted between the shuttle valve and bore. However, the shuttle valve and bore were not worn or damaged.
Manufacturing and Overhaul Details
During manufacturing, the shuttle bore and shuttle valve are honed and lapped as a matching set; clearance limits are not specified. Functional testing is used to detect excessive clearance. Overhaul procedures do not require honing of the shuttle bore. The left actuator was overhauled in August 1998; during that overhaul, the shuttle and end cap were not replaced. The overhauled actuator was installed in February 2000.
Maintenance Omissions
Emergency extension and rigging checks, as required by the airline job card and maintenance manual respectively, were not performed after the actuator installation. The last emergency extension check had been accomplished approximately four months earlier, but the maintenance manual does not indicate that force should be applied to the tires during the extension check using the emergency hand pump.
Accumulated Service
At the time of the incident, the airplane had accumulated approximately 1,475 hours and 1,746 cycles since the actuator installation, and 18,302 hours and 23,315 cycles since the power pack assembly installation.
Power Pack Issue
The power pack motor was found to be inoperative with a load applied.