This paper provides an investigation on the effect of variable inlet guide vane and physical faults on the performance of a three-shaft gas turbine engine at part-load operation. Using the engine manufacturer�s data as input, both design-point and off-design engine performance models have been developed. The model was validated with manufacturer data. Upon validation of the model, the clean engine model was subjected to variable inlet guide vane drift, fouling, and erosion conditions to simulate a degradation state. Two scenarios that cause gas turbine degradation have been considered and simulated: First, how would the combined effect of fouling and variable inlet guide vane drift cause the degradation of the engine performance. Second, how would the combined effect of erosion and variable inlet guide vane drift cause the degradation of the engine performance? The result prevailed that the up-VIGV drift, which is combined fouling and erosion, shows a small deviation because of offsetting the isentropic efficiency drop caused by fouling and erosion. Furthermore, the deviation of performance and output parameters due to the combined faults is discussed following the plots. © Institute of Technology PETRONAS Sdn Bhd (Universiti Teknologi PETRONAS) 2024.