<P> In more advanced systems, such as the US Federal Aviation Administration (FAA) - labeled' Enhanced Flight Vision System', a real - world visual image can be overlaid onto the combiner . Typically an infrared camera (either single or multi-band) is installed in the nose of the aircraft to display a conformed image to the pilot .' EVS Enhanced Vision System' is an industry accepted term which the FAA decided not to use because "the FAA believes (it) could be confused with the system definition and operational concept found in 91.175 (l) and (m)" In one EVS installation, the camera is actually installed at the top of the vertical stabilizer rather than "as close as practical to the pilots eye position". When used with a HUD however, the camera must be mounted as close as possible to the pilots eye point as the image is expected to "overlay" the real world as the pilot looks through the combiner . </P> <P> "Registration," or the accurate overlay of the EVS image with the real world image, is one feature closely examined by authorities prior to approval of a HUD based EVS . This is because of the importance of the HUD matching the real world . </P> <P> While the EVS display can greatly help, the FAA has only relaxed operating regulations so an aircraft with EVS can perform a CATEGORY I approach to CATEGORY II minimums . In all other cases the flight crew must comply with all "unaided" visual restrictions . (For example, if the runway visibility is restricted because of fog, even though EVS may provide a clear visual image it is not appropriate (or legal) to maneuver the aircraft using only the EVS below 100 feet above ground level .) </P> <P> HUD systems are also being designed to display a synthetic vision system (SVS) graphic image, which uses high precision navigation, attitude, altitude and terrain databases to create realistic and intuitive views of the outside world . </P>

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