The purpose of this thesis project is to realize a simulation model of the Environmental Control System of an existing tandem two-seater and turboprop aircraft, in the Matlab-Simulink environment. In the thesis there is a general description of the system, an explaination of the Simulink model with a focus on the modeling of all the components and the mathematical equations used to implement them. Finally the main results are presented, showing a comparation with the results at the company test rig.