Avionic software is more difficult to find its defect compare than graphic user interface based software. According to America’s 「National Transport Safe Board(NTSB)」, most of aircraft accident has been caused primarily by improperly developed software. So airworthiness authority strongly asks to software quality verification in today's avionic software development. 「Air Data Computer(ADC)」is a safety critical system because 「ADC」calculates altitude, speed, temperature and so on. These parameters are used to directly control 「AFCS(Auto Flight Control System)」. Avionic software has to be developed for compliance with avionic software standard i.e. 「RTCA DO-178B」. This paper describes how to apply this standard to the 「ADC」software development and how to verify air data software. In addition, this paper also mentions some additional consideration for software certification.