What happened
The pilot reported experiencing an unsafe indication regarding the landing gear configuration after lowering the system. To verify the status of the nose gear, he utilized an onboard mirror and observed that the nosewheel was not locked in the down position. Consequently, the pilot elected to perform a wheels-up landing.
The investigation
A post-incident physical inspection of the aircraft revealed that the bolt connecting the upper drag link to the nose gear trunition had sheared off. Subsequent laboratory examination of the failed component indicated that the failure mode was consistent with torsional bending fatigue. Specifically, the fracture characteristics were typical of high-cycle, low-load fatigue conditions.
Findings
The investigation determined that the primary mechanical failure was the shearing of the upper drag link attachment bolt. The root cause of this structural failure was identified as high-cycle low-load torsional bending fatigue.