Abstract:
In response to an incident that a 12IV aircraft deviated from the runway after landing, to determine the cause of the malfunction, preliminary analysis and isolation of the cause of the malfunction was conducted through the field investigation and system test. The working principle of the propeller reverse system of the PT6A-27 engine was studied, and operation of the propeller reverse system was described from both hydraulic and mechanical aspects. With the help of theoretical analysis, and in the order of easy to difficult inspection, the cause of the fault was determined to be the failure of the left engine propeller reverse system caused by the fracture of the clamp bolt. The asymmetric thrust generated by the left and right engines caused the aircraft to deviate from the runway. The reasons for the fracture of the clamp bolt were analyzed from the aspects of macro, micro, material composition, metallographic structure, and hardness. The above characteristics indicate that the fracture is caused by stress corrosion. Based on the analysis of the characteristics of the aircraft's marine surveillance operation, it is found that due to long-term low altitude flight near the sea, stress corrosion is formed in the threaded hole area of the clamp bolt. Finally, preventive maintenance measures for this failure are proposed, namely strengthening external wash and scheduled inspections.