What happened
A commercial pilot was conducting a cross-country flight under Title 14, CFR Part 91. Upon arrival at the destination airport, the pilot observed that the landing gear green down and locked light failed to illuminate. The pilot elected to perform a go-around and cycled the landing gear up and down twice; during both cycles, the green down and locked light was visible.
Following the second cycle, the pilot proceeded to land. Upon touchdown, the right main landing gear collapsed. This caused the aircraft to exit the right side of the runway and strike a snowbank. The pilot reported no known mechanical anomalies with the aircraft prior to the accident.
The investigation
A post-accident inspection was performed by an independent aviation mechanic. The inspection revealed that maintenance on the main landing gear did not appear to be in compliance with Airworthiness Directive (AD) 77-13-21, Amendment 39-3093, which became effective on December 16, 1977. This AD specifies the inspections and actions required to maintain the landing gear in an airworthy condition and to prevent malfunction or collapse.
A review of the aircraft maintenance logbooks indicated only partial compliance with this directive. Furthermore, the mechanic noted that several landing gear components were worn significantly beyond the limits established by the AD and its associated service letter.