In currently implemented international aviation strategies and programs, including those realised under the European Union policy, such as Clean Sky, SES, SESAR and, CORSIA, the environmental aspect is particularly prominent – reducing the emission of all gaseous pollutants, and from 2020 also particulate matter. Therefore, it is important to know how the change in flight parameters (altitude, speed) affects the emission of pollutants in jet engine exhausts. Such information will enable to adjust the flight altitude of the aircraft when ecological aspect is taken into consideration. In addition to the operating condition (altitude, flight speed, range of power or thrust), the amount and type of pollutants emitted depends on the type of aircraft, its aerodynamic characteristics, engine type and as well as on the type of fuel used. The impact of changes in aircraft flight parameters (speed and altitude) on the performance of a bypass jet engine and the emission of pollutants in its exhausts is analysed in the paper. For this purpose, the speed-altitude characteristics of such an engine were determined. Next, the emission indexes (EI) for the LTO phase taken from the ICAO database were used to determine the emission indexes corresponding to given parameters of both the engine operation and the aircraft flight. For selected speeds and cruising altitudes, the value of thrust required for the flight of the aircraft was determined and to this value, the engine operation range was assigned as well the corresponding pollutant emission indexes. This allowed to calculate the mass of pollutants emitted per unit of time for given flight parameters. The results obtained are presented in the graphs and discussed.