Event Description
During takeoff, the aircrew heard an unusual 'thud' sound as the landing gear was retracting, but all gear indications were normal. Prior to landing at the destination, three green lights were observed when the landing gear switch was moved to the extend position. A normal touchdown was made, but when the nose was lowered, the aircraft settled on its nose.
Investigation Findings
An investigation revealed that the rod end, part number MS21242S4K, which connects the nose gear to the nose gear actuator, had failed. A metallurgical examination showed signs of high stress fatigue cracking over half of the fracture surface. The fatigue originated in the curve of a thread runout that was corroded. The radius of the curved surface measured 0.056 inch, while the specification MS-21242 required a minimum radius of 0.063 inch.
System Operation
Since the down position switch was connected to the actuator, it had indicated a safe indication when the actuator had operated to the extended position. However, with the rod end failure, the nose gear was hanging in a locked position.