This research presents a model to estimate the influence of the variance of the quality of repair steps on the EGT Margin within the serviceable limits of the overhauled modules. This model is created using literature and a single case study conducted at KLM Engineering & Maintenance Engine services (KLM E&M ES). The model is tested using a data set consisting of all the quality measurements registered during the repair process for two quality contributing modules within the engine. The main research question this thesis is attempting to answer is: How can the quality performance of the engine MRO process steps be used in order to improve the stability of the engine quality output measured in Exhaust Gas Temperature Margin? This research begins with determining how the quality performance of the total engine is influenced. Then, the research is focussed on the gas flow path clearance. Each engine is built up out of sets of fanblades in the compressor and turbine modules. The quality of the engine is measured in degrees of EGT Margin (EGTM) and has a direct relationship to the Time On Wing (TOW) of the engine on the aircraft. Deterioration of the EGTM is mainly caused by increases of the fanblades tip clearances and deterioration of the seals that need to be matched to the casings for each individual set of fanblades. The researched is supported by the case study at KLM E&M ES and is scoped to investigate the CFM56-7B engine used in the Boeing 737 aircraft type and focusses only on the compressor part of the gas turbine consisting of two modules, the High Pressure Compressor (HPC) and Low Pressure Compressor (LPC). In 2017, the quality performance of KLM E&M ES was 67%. For the current state at KLM E&M ES there is a high fluctuation in the delta contractual and actual EGT Margin. Hence, the match between EGT Margin that is agreed on and delivered is unstable. In 73% of the cases where a quality contract is made with the customer, there is an over performance in terms of degrees EGT Margin. The current state quality is controlled by the engineering department which creates a Bill of Work (BoW) where four types of repair possibilities are identified per engine module in order of EGT impact: Full overhaul, Performance restoration, Minimal overhaul or the part is serviceable removed and later assembled as whole. Since the BoW is the only type of quality control within the process, the contractual value cannot be set to a higher standard that can be monetized. This research helps to identify steps within the process where measurements take place that can help to estimate the total EGT Margin contribution value to the engine as a whole. This way, the EGT Margin level can be determined based on the in situ measurements and the goal is a closer match to the contractual EGT Margin values with the actual ones. This research is concluded with a future state analysis where a Matlab model of the Low and High Pressure Compressors is created. The Matlab model is based on the Engine Service Manual and Workscope Planning Guide with the goal to simulate the impact of decreases in variance of the fanblades sets. The model is validated and tested using the KLM E&M ES case study with the actual handwritten quality performance registrations on piece part level. For the HPC, the limits of fanblades repairs has a bandwidth of 5 microinch in which the repair is considered serviceable. This 5 microinch influences the EGT Margin with 3,7 degrees EGT Margin potential for the HPC. When the lowest blades within a set are replaced, the maximum potential EGT margin that can be gained is 1.6 degrees EGTM. The Matlab model shows that the largest potential EGT gain is in stage 8 of the High Pressure Compressor. The variance at KLM E&M ES is the highest in stage 8 and 9. The decrease of the variance can result in a potential of 11 weeks Time on Wing. This research ends with recommendations for further research. A similar study is needed on the quality contribution of the combustor and turbine assy’s. Finally, this research can be continued in order to create a model for EGT Margin estimation for the CFM56-7B engine. A hypothesis for continuation of this research is formulated as follows: The quality of the CFM56-7B engine in terms of EGT Margin can accurately be predicted using the repair step measurements of the combustor, compressors and turbines.