The paper presents a model of the aircraft turnaround process at airport apron. Airlines have an interest for an efficient and reliable turnaround process which allows them to maintain schedules. The process should also be as fast as required so that aircraft are flying rather than sitting on the ground, incurring losses and extra costs. This is the reason why the turnaround process needs to be studied, planned and executed in an efficient manner. This turnaround process model has been developed to investigate different resource allocation strategies (aircraft stands, equipment, personnel, etc.) and sensitivities to perturbations, their possible prevention or mitigation of their effects. The model is a rather sophisticated one, using Petri nets as a powerful tool for modeling and simulating discrete processes with concurrent events. This type of model could also easily be incorporated into a larger scale model of airport operation. The model's capabilities are illustrated using real life examples from the Belgrade airport.