Wireless Avionics Intra-Communication (WAIC) is the standard of future avionics communications systems, aimed to substitute wired-communication in a single aircraft. The WAIC systems are designed for enhancing the efficiency and reliability communications systems of the aircraft. Currently, the standardization issue is focused on the allocated frequency band. The frequency of 4.2 - 4.4 GHz will be decided by the ITU as the main spectrum band; while the band of 22-23 GHz is still investigated. This paper develops the compatibility model of WAIC system, presenting the simulation and analyses of the interference scenarios between WAIC and Fixed Services at 22- 23 GHz. The first scenario deals with condition to protect WAIC from Fixed Service's interference emission. The second scenario is condition to protect Fixed Service by investigating the protection criteria between Fixed Service and aircraft in the airport. The results have signified separation distances that should be fulfilled to maintain compatibility between WAIC and Fixed Service systems at the frequency band of 22-23 GHz.