The aim of the thesis is to analyze and compare the emissions of subsonic, supersonic and hypersonic aircraft through the Boeing Fuel Flow Method. In the first part of the work, a relationship was searched between the fundamental quantities of each subsonic engine, Overall Pressure Ratio and By Pass Ratio, and polluting emissions, through the analysis of the ICAO database. A Matlab code was therefore used to read and save the data reported in the Excel database, then interpolating them according to various criteria. Subsequently, starting from the same data, a Matlab code was developed to calculate the Emission Index of each engine through the Fuel Flow Method, and to be able to have an indicative value of emissions during a typical mission.