Some background to the theme of the research will hopefully set the scene. Flight simulators have become integral to the manufacturing, training and research communities and their utilisation is expanding rapidly. However, despite the sophistication and advancement of modern technology, simulators are inherently incapable of providing an exact representation of reality, due largely to incomplete mathematical modelling of the aircraft and its systems on the one hand and the physical limitations of the motion and visual cueing on the other. In the training context, an important issue in the development of the qualification standards is the criteria used to prescribe the fidelity of devices and the engineering basis underpinning them. Component fidelity, which may simply be a reflection of the state of the art , is important, but the standards also require piloted assessment of the integrated system with typical mission sorties flown covering the training aspects for which the system will be used. Subjective opinion here is important too because it reflects the value that an experienced pilot places on the level of realism. Quantifying overall simulation fidelity is more difficult however, but is equally important because, arguably, component or sub-system fidelity can only be properly related to fitness for purpose if connected by measurement of the whole. To provide a framework for the acceptance of synthetic training devices, regulatory authorities have produced performance standards along with associated training credits, specifying criteria for the cueing environment (motion, visuals, control loading system, audio etc) and the aircraft flight dynamics models. Historically, the standards have grown out of the requirements for fixed-wing simulators and there is a real and urgent need for a substantial engineering basis for rotorcraft simulation fidelity. This is the focus of the proposed research programme, which aims to bridge the gap between pilot subjective opinion and formal metrics. For example, the current process for validating mathematical models involves the development of a physical model with a required accuracy, followed by implementation of the model in the simulator. A validation process then requires a rigorous checking of the simulator against specified tolerances followed by piloted evaluations of predefined test manoeuvres. To complete the process, the results of the tests are compared with flight test data and the discrepancies identified by the pilots are 'corrected' through a 'tuning' process, where modifications are made to the model or simulator systems in order to improve the 'realism'. This tuning process will be placed on a firmer engineering basis in teh proposed research.The PI's research, in collaboration with European Industry, has shown that, in most areas, 80% fidelity should be achievable with physical modelling and the remaining 20% requires artificial tuning, yet is critical for acceptance. While tuning may be able to correct problems in a specific flight condition, it often has an adverse affect in other parts of the flight envelope. Thus, to achieve an acceptable level of performance, modifications are implemented which are not physically realistic and difficult to justify from an engineering standpoint. What is clear is that there is limited understanding of the relationship between the settings of the simulator cueing environment and the behaviour of the pilot. Industry practice for the tuning process is usually commercially sensitive and certainly not in the public domain. What is required is an objective means for assessing the overall fidelity of a simulator, to complement the perceived fidelity and the predicted component fidelity; this is the focus of the proposed research.