Copyright © 2021 by the Vertical Flight Society. All rights reserved.The Applied Vehicle Technology (AVT) Panel of the NATO Science and Technology Organization has recently engaged a Research Task Group on the topic of rotorcraft flight simulation model fidelity. This group aimed to explore a comprehensive set of methods for flight mechanics simulation fidelity enhancement, including training simulation applications. Particular effort was also directed to the metrics used for simulation fidelity model assessment as suitable for the final intent of the model. The work presented in this paper was carried out in the framework of this Research Task Group, AVT-296, which examined seven different approaches; our paper focusses on just one of these. The objective was to assess flight-model renovation methods through four different applications. As a common approach, flight data from various helicopters were used to extract a set of flight dynamics information (state and control derivatives) that were used to compute corrective force and moment terms. The approach consists of a comparison between flight-test and flight mechanics model derivatives to compute delta forces and moments. These delta terms are added to the forces and moments through a linear combination and to generate the additional accelerations needed to capture any lacking dynamics. The derivatives that require updating need to be identified and, of course, will depend on the nature of the modelling deficiency. This paper shows how this method is applied to enhancing the lateral-directional oscillatory characteristics of flight models and how they can be upgraded to achieve higher fidelity for design and development applications but with special attention to meeting the fidelity requirements for flight training simulators.