Abstract. Nowadays, multilateration systems are widely used for locating the aircrafts. One of the challenges in implementation of the system is placing receivers in appropriate locations which are dependent to several factors such as delay spread. By modeling power delay profile, delay spread can be obtained. In this article, two airports of Iran were considered and ray tracing method was applied to them for calculating delay in multiple paths. Then by using the results and LSE method, cost-207 model was modified for receivers in different areas of the airports. Ray tracing method and modified cost-207 can be used for specifying appropriate areas for multilateration receivers in those airports. The same algorithm can be used for the other airports with the similar structure.