Night Vision Goggles

its about my life

uNight vision goggles? Aren't they for the military and police? Not anymore! On January 29, 1999, the FAA issued the first Supplemental Type Certificate (STC) to permit use of night vision goggles by a civilian helicopter EMS (emergency medical service) operator. Since then several more have been issued to other commercial operators. In addition, rulemaking was initiated (but at the time of this writing is temporarily on hold) for changes to FAR Part 91 that would permit use of this technology by general aviation pilots. With this in mind, it will only be a matter of time before pilots start hearing more and more about these significant aids to night flying. Therefore, it is important for pilots to become aware of this technology and understand some of the basic operational issues.

NIGHT VISION GOGGLES

Night vision devices include a variety of different technologies, such as forward-looking infrared radar (FLIR) and night vision goggles. The focus of this article will be on night vision goggles, more commonly known by the acronym NVG. The simplest analogy to explain how NVG's work is a video camera. The basic principle is the same in that the user is not directly seeing what they look at, but rather is viewing an electronic image of the scene.

NVG equipment may be monocular or binocular. However, in aviation, binocular, helmet-mounted equipment is almost exclusively used. Like a video camera, an NVG is an electro-optical device. Electromagnetic energy, both visible and infrared, reflected from the terrain at night enters the NVG through the objective lens. These photons of light energy are directed to an electronic processing unit called the image intensifier, which contains several components. The photocathode element in the image intensifier converts the light photons to electrons and moves them to the microchannel plate (MCP) which accelerates and multiplies them several thousand times. The electrons then strike the phosphor screen, which is ultimately responsible for emitting the visible light the user will see through the eyepiece lens as a focused image.

Unlike the video camera, the NVG does not require much light to produce an image. Light as faint as a starlight or low-level moonlight will suffice. However, the efficiency of the equipment will be degraded in total darkness or with too much light. The image intensifier will increase what little light energy there is on average several thousand times. State-of-the-art NVG's are capable of intensification on the order of 35,000 times or more. That amplified or intensified energy is projected onto the phosphor screen, which creates the visible image the user-sees through the eyepieces. The NVG image is monochrome, i.e., in one color, typically either green or amber depending on the type of phosphor used. NVG equipment lacks the ability to produce a multi-color representation of a scene.

Aviation NVG models are helmet-mounted with electrical power supplied by a battery pack attached to the back of the helmet. As with any optical device, the user has a variety of ways of adjusting fit and focus. The NVG binoculars and mounting assembly are cumbersome, weighing approximately one pound. In addition, one must factor in the weight of the helmet and battery pack.

ADVANTAGE OF NVG's

The advantages of this night vision aid technology in aviation can be summed up as an increase in nighttime situational awareness for pilots. This technology does not turn night into day, but it does permit the user to see objects that normally would not be seen by the unaided eye. This would markedly decrease the possibility of collisions with terrain or man-made obstructions. Many other benefits exist, but the bottom line is that this technology, when properly used, has the potential to significantly increase nighttime flying safety.

DISADVANTGAGES OF NVG's

Unfortunately, this increase in safety comes with a significant price. Some of the disadvantages of NVG's include:

* decreased field of aided view

* decreased visual acuity