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Head-up displays (HUDs) or helmet-mounted displays (HMDs) that provide pilots with world-referenced symbology or imagery require critical alignment and minimal time delays. In this paper, some aspects of system accuracy and latency will be discussed in the context of the Enhanced and Synthetic Vision System (ESVS), which is displayed on an HMD. In a joint program, the Canadian Department of National Defence (DND), CAE Inc., CMC Electronics, and the Flight Research Laboratory of the National Research Council of Canada integrated and flight-tested an enhanced and synthetic vision system. The goal of the program was to examine the potential of the ESVS concept for search and rescue operations. Despite obvious misalignments between the enhanced and synthetic images, the current system demonstrated the potential of ESVS systems with most of the test pilots able to navigate at low altitude in low visibility in an area without prepared navigation aids. The flight tests highlighted the system potential- the synthetic imagery provided continuous virtual VFR conditions, while the enhanced sensor generally provided more accurate spatial data and obstacle avoidance information. The ESVS program finished with the first helicopter flight test of both enhanced and synthetic visual displays presented on an HMD. While this milestone was successfully achieved, there is clearly a need for improved technology and further research to implement safe and effective ESVS systems. The system alignment was found to be a complex and perplexing issue. It was not possible to align the system within the precise tolerances generally accepted for HUD-equipped aircraft and, in fact, errors that were an order of magnitude greater than the recommendations were common. Errors built up in such a way that the system developers needed to develop an interim alignment solution and pilots were forced to deal with relatively large angular offsets. This was less than optimal, but proved to be sufficient for the tasks in the trials. However, it is clear that a rigorous alignment procedure is required to satisfy the strict requirements of an all-weather system that would support aggressive maneuvering and navigation in unknown terrain.
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