Aircraft landing system is the critical system to ensure the safe approach and landing of aircraft, and how to evaluate the landing system to meet the safety design requirements is one of the important parts of the system design. The basic process of the safety assessment for the civil aircraft is described. Taking the microwave landing system (MLS) as an example, for a given MLS block diagram, the failure condition complete loss of both sides MLS information is evaluated by the fault tree analysis (FTA) method. The process and method of tree modeling are described in detail. The results show that FTA plays an important role in the design of the system architecture. The FTA and system architecture design are closely combined and feedback each other. Especially when the probability requirements associated with the failure condition cannot be met, the FTA cutset report can find the weaknesses and key parts of the system architecture, so as to take effective measures to complete the optimization design of the system architecture.