In this study, Fuzzy Expert Systems in Aviation is inspected and a fuzzy expert system is designed to provide solutions on aerospace vehicles' airworthiness evaluation and mission planning. In aviation aspect, mission planning is a rather complicated process consisting two main parts, operations management and maintenance, and requires many different criteria must be evaluated and met. This research is intended to be a supportive solution for the mission planning process, to which the flight safety is the most important issue, and for the planning task that is human-based and expects many inputs and needs to be done flawlessly. A fuzzy expert system structure has been developed according to the process. Stages applied respectively; creating a database, fuzzification, rule based inference process and defuzzification. The research shows, this process can be solved effectively by using a web based fuzzy expert system.