In this paper, based on system theoretic process analysis (STPA) method, the system level hazards of aircraft landing gear retraction system were identified and determined, and the behavior principle block diagram model of human-machine control, system functional action and feedback of the whole operation process of the system was constructed. The unsafe control action (UCA) in the operation process of the system was identified and the risk factors

leading to UCA were analyzed. The research showed that the method can not only enable identification of all component physical failure factors recognized by traditional safety analysis methods, but also identify risk factors leading to UCA incidents resulting from human-machine interaction, such as position and actuate on control unit

(PACU) core processor algorithm delays and crew member misoperation. The research results of this paper can

provide theoretical basis and methodological support for safety analysis of the entire process for civil aircraft development and application.

landing gear retraction system, risk identification, risk analysis, system theoretic process analysis (STPA)