Incident Description
During the landing rollout, while the airplane was at a speed of about 100-120 knots and the thrust reversers were deployed, the airplane began to lean and veer to the right. The captain initially attributed this to crosswind but soon realized the landing gear had collapsed. The airplane was positioned near taxiway T-2 when the lean began and came to a stop near taxiway U. The flight crew evacuated the airplane onto the taxiway via the L1 door slide.
Investigation Findings
Examination of the digital flight data recorder (DFDR) and cockpit voice recorder (CVR) by the National Transportation Safety Board (NTSB) revealed parameters and conversations consistent with a normal landing. Disassembly of the right main landing gear torque tube showed that the outboard torque tube attach bolt had backed out from the piston prior to the incident. The attach bolt, which is threaded and has a hole drilled in the end, is normally torqued to 475 ft-lbs and secured with a lockbolt through the hole.
Maintenance Issues
According to the operator's Manager of Quality Assurance, the attach bolt was not properly torqued and the lockbolt was installed, but not through the hole in the end of the attach bolt. Consequently, after 11 cycles, the attach bolt backed out of the threaded area of the piston, leading to the collapse of the right main landing gear. The QA Manager further stated that during installation, a maintenance personnel shift change had occurred, and the new shift was not informed by the outgoing shift of the work still to be accomplished, resulting in incorrect reassembly of the right main landing gear.
Examination of Components
Damaged landing gear parts were collected and sent to the NTSB's Metallurgical Laboratory in Washington, DC, where optical examination revealed signatures consistent with overstress separations. No preexisting cracks or corrosion were noted.