Incident Description
During ground operations, the aircraft was executing a right-hand turn at slow speed in the run-up area when the left main landing gear collapsed. The incident occurred without any prior indication of structural failure.
Examination Findings
Detailed examination of the left main landing gear assembly revealed that the side brace, which is attached to a casting bolted to the inboard wing rib within the landing gear wheel well, had become detached from its normal position. The wing rib web had fractured around the casting, allowing the side brace to move and the landing gear to collapse. Notably, portions of the crack exhibited discoloration, suggesting that the crack had been present for an extended period prior to the incident.
Maintenance and Inspection History
A review of the aircraft's maintenance records disclosed no history of landing gear damage or hard landing events that would have required repair. The last annual inspection occurred 7 months and approximately 60 flight hours before the incident. No evidence of any recent maintenance activity related to the landing gear or wing structure was found.
Manufacturer Service Information
The aircraft manufacturer, Cessna Aircraft Company, had previously encountered instances of cracking in the inboard wing rib web surrounding the side brace fitting. To address this, Cessna issued Service Letter ME76-2 on January 5, 1976. The service letter outlined the installation of a steel reinforcement doubler plate on the wing rib web behind the landing gear side brace fitting. Inspection of the incident aircraft confirmed that this service letter had not been accomplished.