Fuel tank system ignition source failure threatens the safety of the aircraft. For different possible ignition sources in and around the fuel tank system and their airworthiness requirements, this paper proposes a particular method using both Failure Mode and Effects Analysis (FMEA) and Fault Tree Analysis (FTA) to analyze the ignition source fail-safe features, which can minimize the hazards caused by the ignition sources failure and improve the safety of the whole aircraft. At last, an example is given, which proves the efficiency of the method.