The basic composition of general aircraft avionics were summarized by studying the basic functional requirements and system characteristics in this paper. Classification requirements of failure conditions for typical functions such as atmosphere, attitude, communication, navigation and monitoring were studied by analyzing the relative airworthiness regulations. For typical class Ⅱ turbine general airplane, the redundancy requirement of major functions of the avionics system were studied by fault tree analysis in order to meet the requirements of the typical functional failure probability and basic logic architecture of system was obtained.