One of the most common causes of fatal helicopter accidents is Controlled Flight Into Terrain (CFIT) at night. (FlightWeb). The major contributor to such accidents is the pilot's level of situational awareness, or rather not being able to see where they are going, or what might be in the way of unobstructed flight. As helicopters are routinely used in low-altitude missions they are frequently required to fly in close proximity to trees, power lines, telephone poles, etc. As such, it is vitally important for the pilot to be able to see and avoid these hazards to navigation. During daylight hours, these hazards pose a minimal risk to flight. However, as the sun sets and the amount of visible light wanes, these same hazards become life threatening. The reliance on night vision technology has become invaluable in assisting aviators in flying at night. By magnifying the ambient light, Night Vision Goggles (NVG's) and devices reduce the problems associated with unaided vision in the dark. The Human Eye and Night Vision Goggles
Vision is a physical sense that uses light to provide information to the brain in order to make conclusions about the surroundings. The human eye is an intricate organ that works best when there is an adequate supply of light. Our eyes have been often compared to cameras in that a camera filters light through the lens, controls the intensity with an aperture and focuses the image onto a film. Light coming into an eye is filtered through the cornea, the iris regulates how much light comes through, and then it is focused by the lens onto the retina. During the day, we are able to detect color, depth perception, distance and visual acuity. At night, all of those senses are greatly diminished. Visual clarity can be reduced to 20/200 or greater at night. The sensitivity of the retina (where images are focused) is greatly hindered when the light levels drop. On a clear night (with a full moon and no clouds), the unaided...
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Ahern, Patti. "Flying Through the Dark". Helicopter Monthly Online Magazine. November 1, 2004. http://www.helicoptermonthly.com/detail.cfm?&ItemID=210&CategoryID=13.
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