Interest in air transportation in the last decade has seen aviation fleet growth and a rise in the energy consumption of aircraft. In accordance with the latest data, the air transportation sector consumes 7.5% of total oil consumption worldwide. This high share by air transportation forces designers and researchers to develop more efficient propulsion systems by considering the constant rise in energy costs. In the current paper, an exergy based sustainability assessment of a turbojet engine under design point conditions is presented while two novel ecological performance indicators, namely the ecological objective function and ecological coefficient of performance, are introduced for the turbojet engine. These ecological performance indicators can be considered useful for improving the efficiency of any turbojet engine. As a result of an exemplifying analysis, the exergy efficiency, exergy sustainability index, ecological objective function and ecological coefficient of performance have been calculated to be 50.13%, 0.503, 68.294 kW and 1.005, respectively. In the light of the results, the author concludes that the exergy destruction rate of the turbojet engine should be minimized to improve the sustainability index and ecological coefficient of performance, while increasing or maintaining a constant thrust of the examined turbojet engine.