The aim of this study is to develop an accurate and reliable method for estimating the propagation characteristics inside and outside aircraft cabins so as to advance the radio link design techniques for WAIC systems. This paper uses the FDTD method and large-scale parallel computing to conduct the world's first study on the propagation characteristics of signals emitted by a transmit antenna above the wing tip to WAIC antennas installed inside and outside the aircraft cabin (Airbus 320-200). EMF distributions created by a 4.4 GHz wireless transmitter inside the cabin are analyzed and propagation characteristics are determined from the analysis results.