Incident Overview
The flight crew received an unsafe nose gear indication while on approach to landing. After recycling the landing gear, all cockpit indications showed the gear was down and locked. The aircraft landed on runway 4R. Upon touchdown, the nose gear collapsed, and the airplane skidded to a stop on the runway.
Investigation Findings
Post-incident examination of the aircraft revealed that the nose landing gear upper lock link had fractured. The lock link had accumulated 28,978 service hours and 24,511 cycles since its original manufacture. It had been overhauled 13,515 hours and 6,317 hours prior to the failure. Metallurgical analysis showed that the upper lock link fractured through the 'I' beam section near its lower end, approximately 3 inches from the overcenter pivot with the lower lock link. The fracture features were consistent with fatigue that had progressed over a large portion of the fracture surface. No mechanical, corrosion, or manufacturing discontinuities were observed at the fatigue origin.
Maintenance History and Airworthiness Directive
At the time of the incident, Airworthiness Directive AD-97-02-10 was in effect regarding the upper lock link. This directive required inspections of assemblies before reaching 10,000 total cycles or within 90 days of its issue date of February 11, 1997, whichever occurred later. Continental Airlines was in the process of inspecting its entire fleet of affected aircraft when this incident occurred.