Abstract: The fracture surface of an aircraft landing gear hub and the metallurgical quality of ZM5T4 cast magnesium alloy as well as the damage feature of its related components (bearing,shaft)were examined by metallography, X\|ray defectoscopy, fractography and infrared spectrometry in laboratory. The appearances of fractosurfaces simulated at various testing temperatures were obtained. Fracture of the hub was brittle intergranular fracture at high temperature. Local fracture temperature approached the materials binary eutectic temperature. Laboratory examination and airfield investigation results indicated that the failure of the hub was not related to metallurgical quality, but to the small assembling gap of the landing bearing system. It induced poor lubrication, scratch and high temperature crack of the bearing component and the hub. The small assembling gap of the bearing system was considered to be the basic cause of the aircraft landing gear hub failure at high temperature.

Key words: landing gearhub, fracturing, accidents　analyzing