A scientific method is developed to determine the impact of a deteriorated HPC (high-pressure compressor) on the overall performance of a turbofan jet engine. Initially, the HPC performance with roughness variations on vanes and blades is simulated by using 3D CFD (Computational Fluid Dynamics) at different operating points. Afterwards, the overall performance of the full jet engine is computed by the in-house 1D performance tool ASTOR (AircraftEngine Simulation for Transient Operating Research). ASTOR is based on the Pseudo Bond Graph approach to model and connect miscellaneous components with the equations of motion and dynamic volumes. By solving this differential equation system, transient performance is calculated in higher accuracy compared to common Reduced Order Models (ROM). Transient load cases are modelled to analyse the impact of deteriorated HPC on the overall performance. Furthermore, similarities and differences to the steady performance are considered. The maximum deviation of EGT between an engine with a new and deteriorated HPC during a fast acceleration is 32% while it is 27% at steady operation. Also a trade-off between an increasing EGT and a decreasing pressure downstream of the LPT is analysed. Finally, relations between the engine performance, Reynolds-number and roughness are analysed to classify the performance drop due to a HPC with roughness.