WAIC (Wireless Avionics Intra Communications) is a wireless communication system connecting the avionics in the aircraft. This system is currently researched by AVSI (Aerospace Vehicle Systems Institute), ICAO (International Civil Aviation Organization), and ITU (International Telecommunication Union) to substitute cable redundancy in the avionics system. Current stage of the development is to determine the bandwidth for WAIC. The frequency band 4200 - 4400 MHz is the most recommended band for the WAIC system. This paper investigates and analyzes the compatibility of the WAIC system to radio altimeter at 4200 - 4400 MHz. The compatibility simulation is represented by the interference of WAIC to radio altimeter receiver. The four parameters of radio receiver are used in this simulation namely front end overload, receiver desensitization, false altitude report, and power spectral density. The scenario used in this simulation consists of two conditions that are LI (Low Inside) and HI (High Inside). Those conditions are applied to the aircraft that is in the landing phase. The results of the compatibility present that the interference of the WAIC system is not harmful to the radio altimeter. As a result, the frequency 4200 - 4400 MHz is suitable for WAIC.