An Instrument Landing System (ILS) is a ground-based instrument approach systemrnthat provides precision guidance to aircrafts approaching and landing on a runwayrnusing combinations of radio signals. There are three components of ILS; namely,rnlocalizer (LOC), Glide slope (GP) and Distance Measuring Equipment (DME) or series ofrnmarkers. LOC is used by the pilot to determine the location of the airplane relative to therncenterline of the runway; GP provides the slope information (inclination angle) andrnDME distance from the beginning of the runway. Among the three ILS subsystemsrn(components) this thesis focuses on LOC which is operating from 108.1 MHZ to 111.975rnMHZ. This frequency range is prone to adjacent channel interference from FrequencyrnModulation (FM) broadcasting systems that are operating from 87.5MHZ to 108MHZ. rn In the past few years there is an increase in number of FM broadcasting radio stations inrnAddis Ababa. FM broadcasting stations are likely to cause intermodulation interferencernto the ILS LOC, hence, posing a great risk to aircraft navigation safety. This thesisrnaddresses interference of Addis Ababa Bole international airport RWY 25 ILS localizersrnand analyzes the interference mechanism. rnThe study accomplished through the establishment and implementation of modelsrnregarding the characterization of the transmitter and its signal, as well the definition ofrnthe aircraft approach path. Model development was done from the bases of fieldrnmeasurements of ILS LOC power level on a certain approach rout and then translates rneach parameter into defining the scenario. Furthermore, the assessments of interferencernwere performed by using two criteria. One consisted on the raw analysis of the ratiornbetween the LOC signal power and interfering signals power, and the other is based onrnan International Telecommunication Union (ITU) Recommendation. The results verifiedrnthe non-existence of any harmful interference generated by Addis Ababa commercial FMrnbroadcasting networks on ILS LOCs runway (RWY) 25 heading for the time being. rnHowever, the results also indicate that there is interference RWY 07, though it is not rnbeing operational for the time being.