In this study, an exergy analysis of a turbofan engine, being the main power unit of an UAV (unmanned aerial vehicle) over the course of a surveillance mission flight, is presented. In this framework, an engine model is firstly developed, based upon engine design parameters and conditions using a genuine code. Next, the exergy analysis is performed according to thermodynamic laws. At the end of the study, the combustion chamber is identified as the most irreversible component of the engine, while the high pressure turbine and compressor are identified as the most efficient components throughout the flight. The minimum exergy efficiency is 58.24% for the combustion chamber at the end of the ingress flight phase, while the maximum exergy efficiency is found to be 99.09% for the high pressure turbine at the start of the ingress flight phase and landing loiter. The highest exergy destruction within the engine occurs at landing loiter, take-off and start of climb, with rates of 16998.768 kW, 16820.317 kW and 16564.378 kW respectively. (C) 2015 Elsevier Ltd. All rights reserved.