Unmanned Aircraft System (UAS) is playing a more and more important role in military as well as civil areas, pushing UAS to be more quickly integrated into the existing airspace management system. UAS has a series of unique airworthiness characteristics with respect to the technologies, thus we shoud focus on the development of UAS-specific airworthiness standards and their demonstrations. This paper investigates the airworthiness standard(CS-23) of manned aviation and the tailoring of it to be applicable to UAS, namely STANAG 4671. This is conducive to the solutions of UAS technical issues and the development of civil UAS airworthiness standards.