The Bombardier CRJ on 14 December 2008 landed in Philadelphia with its left main landing gear retracted, which caused damage to the aircraft's left wing, aileron and flap.
During its investigation the NTSB determined the aircraft underwent extensive maintenance that included the removal, replacement and visual inspection of the left and right main landing gear uplock assemblies. Work performed on the assemblies was identified as a required inspection item.
NTSB's investigation revealed that the mechanic who replaced the left uplock assembly had not completed uplock assembly work previously, received no on-the-job training for the task and was not supervised during the procedure.
The left uplock assembly, upper attachment bolt, nut and cotter pin assembly used to mount the left main landing gear to the structure were installed, but did not engage the uplock assembly. As a result the uplock assembly pivoted about to the lower bolt.
Since the upper attachment bolt did not engage the uplock assembly, the left main landing gear remained in the up-and-locked position, and did not respond to pilot commands to lower before landing. The NTSB's investigation revealed that post-maintenance inspections were not adequate to detect mis-rigging of the uplock assembly.
With the investigation complete, the NTSB recommendations to the Federal Aviation Administration include requiring mechanics performing required inspection items and other critical tasks, and required inspection item inspectors, to receive on-the-job training or supervision until they demonstrate proficiency.