What happened
During the landing rollout, while traveling at a speed between 100 and 120 knots with thrust reversers deployed, the aircraft began to lean and veer to the right. The captain initially suspected a crosswind but realized the landing gear had collapsed. The aircraft was positioned near taxiway T-2 when the veer began and came to a stop near taxiway U. There were no injuries reported, and the flight crew evacuated the aircraft via the L1 door slide.
The investigation
The NTSB examined the digital flight data recorder (DFDR) and cockpit voice recorder (CCVR). Data from the DFDR indicated a normal landing had been performed, and the CVR contained conversations in Spanish consistent with a normal landing.
Investigators disassembled components of the right main landing gear torque tube and found that the outboard torque tube attach bolt had backed out from the piston prior to the incident. The assembly process requires the threaded attach bolt to be torqued to 475 ft-lbs, followed by the installation of a lockbolt through a hole in the end of the bolt to retain it.
Examination of damaged landing gear parts at the NTSB's Metallurgical Laboratory revealed signatures consistent with overstress separations, though no pre-existing cracks or corrosion were found.
Findings
Investigation revealed that the attach bolt was not properly torqued and the lockbolt was installed without passing through the hole in the end of the attach bolt. This allowed the bolt to back out after 11 cycles, resulting in the collapse of the right main landing gear. The operator's Manager of Quality Assurance stated that a maintenance personnel shift change occurred during the installation of the right main landing gear; the incoming shift was not informed of the remaining work, which led to the incorrect reassembly.