Ice crystal ingestion to aircraft engines may cause ice to accrete on internal components, leading to flameout, mechanical damage, rollback, etc. Many in-flight incidents have occurred in the last decades due to engine failures especially at high altitude convective weather conditions . Thus, in the framework of HAIC FP7 European project, the physical mechanisms of ice accretion on surfaces exposed to ice-crystals and mixed-phase conditions are investigated.Within the HAIC FP7 European project, TAI will implement models related to the ice crystal accretion calculation to the existing ice accumulation prediction program for droplets, namely TAICE. Considered models include heat transfer & phase change model, drag model and impact model. Moreover, trajectory model and Extended Messinger Model require some modifications to be used for ice crystal accretion predictions.For drag coefficient calculations, Ganser model has been chosen as the most applicable among the models found in the literature for non- spherical particles and was implemented to the program . However, for some flow conditions, this drag model deviates from the experimental results. Thus, by including existing models [3, 4], effect of drag models on collection efficiency will be studied in this paper. Moreover, for heat transfer and phase change parts, ONERA model is used due its simplicity and easily applicability . For convective heat transfer coefficient estimations, Integral Boundary Layer Method is currently being used . However, more accurate heat transfer models are required in complex porous ice-water layer predictions and it should be taken into consideration as one of the primary issues for ice crystal accretion calculations. Moreover, impact model including bouncing, fragmentation and partially sticking will improve the accuracy of the prediction and an upgraded version of the Extended Messinger Model will be achieved with those modifications.