Incident Overview
An aircraft received minor damage after its pilot performed an emergency landing with the landing gear partially retracted. The main landing gear (MLG) failed to extend despite multiple attempts using normal, abnormal, and manual extension procedures. The aircraft touched down with the nose landing gear (NLG) extended while the main gear remained retracted.
Investigation Findings
Examination of the landing gear system revealed that the left MLG door actuator pivot trunnion upper shaft had fractured due to fatigue. After the break, the separated shaft became lodged between the trunnion and the actuator clevis, preventing the manual door unlock mechanism from releasing. This blockage rendered the manual extension procedure ineffective.
Part History and Maintenance
A review of service difficulty records for the failed component indicated that several similar failures had occurred on other units of the same manufactured part. The investigation noted that a redesigned replacement part was available. The operator had performed all required inspections for the landing gear system in compliance with maintenance directives.
Conclusion
The failure of the left MLG door actuator pivot trunnion upper shaft from fatigue fracture led to the gear malfunction. No other causal factors were identified.