Abstract: During the operation of a certain type of fan, the fifth stage planet carrier in its yaw drive cracked. The fracture reasons were analyzed by means of macroscopic observation, chemical composition analysis, scanning electron microscopy and energy spectrum analysis, mechanical property test, hardness test and metallographic examination. The results show that the impact absorption energy of the planet carrier was low, and the impact resistance was poor. When the passive yaw slip occurred, it beared a large impact load, and cracks were generated at the maximum stress. The cracks expanded rapidly in a short time, which eventually led to brittle fracture of the planet carrier.