采用宏、微观检验方法对国外某航空公司波音747SP飞机主起落架收放作动筒断裂性质和原因进行了分析。查明作动筒断裂性质为腐蚀疲劳，腐蚀疲劳起源于作动筒外壁表面的网状裂纹，而这些网状裂纹产生于电镀之前，是一种加工缺陷。作动筒表面裂纹的网状形态以及初始深度符合磨削裂纹的特点。

Fracture analysis on the retractable actuator of the main landing gear of a Boeing 747SP airplane of a foreign airlines has been conducted by means of macroscopical and microcosmic fracture surface analysis and crack metallurgical analysis. The results indicated that the fracture of the actuator was of corrosion fatigue. The corrosion fatigue cracks initiated from the surface cracks that are in net shape in the outer wall of the actuator. These surface net cracks had been formed before plating of the actuator, so these cracks are a kind of machining defect. The net shape and original depth of these surface cracks conform to the character of grinding crack.