Aeromedical Factors

Focal points X 10 degrees X X X 10 degrees 10 degrees OBSERVER Once an object is detected in the peripheral field of dark- adapted vision, continued surveillance is maintained by use of “off-center” vision. Looking 10° right or left and above and below the object, viewing no longer than 2 to 3 seconds at each position. X 10 degrees Figure 17-19. Off-center viewing. Sunglasses High Intensity Lighting If a night flight is scheduled, pilots and crew members should If, during the flight, any high intensity lighting areas are wear neutral density (N-15) sunglasses or equivalent filter encountered, attempt to turn the aircraft away and fly in the lenses when exposed to bright sunlight. This precaution periphery of the lighted area. This will not expose the eyes to increases the rate of dark adaptation at night and improves such a large amount of light all at once. If possible, plan your night visual sensitivity. route to avoid direct over flight of built-up, brightly lit areas. Oxygen Supply Flightdeck Lighting Unaided night vision depends on optimum function and Flightdeck lighting should be kept as low as possible so that sensitivity of the rods of the retina. Lack of oxygen to the rods the light does not monopolize night vision. After reaching (hypoxia) significantly reduces their sensitivity. Sharp clear the desired flight altitude, pilots should allow time to vision (with the best being equal to 20–20 vision) requires adjust to the flight conditions. This includes readjustment significant oxygen especially at night. Without supplemental of instrument lights and orientation to outside references. oxygen, an individual’s night vision declines measurably at During the adjustment period, night vision should continue pressure altitudes above 4,000 feet. As altitude increases, to improve until optimum night adaptation is achieved. When the available oxygen decreases, degrading night vision. it is necessary to read maps, charts, and checklists, use a dim Compounding the problem is fatigue, which minimizes white light flashlight and avoid shining it in your or any other physiological well being. Adding fatigue to high altitude crewmember’s eyes. exposure is a recipe for disaster. In fact, if flying at night at an altitude of 12,000 feet, the pilot may actually see elements Airfield Precautions of his or her normal vision missing or not in focus. Missing Often time, pilots have no say in how airfield operations are visual elements resemble the missing pixels in a digital image handled, but listed below are some precautions that can be while unfocused vision is dim and washed out. taken to make night flying safer and help protect night vision. • Airfield lighting should be reduced to the lowest For the pilot suffering the effects of hypoxic hypoxia, a simple usable intensity. descent to a lower altitude may not be sufficient to reestablish vision. For example, a climb from 8,000 feet to 12,000 feet for • Maintenance personnel should practice light discipline 30 minutes does not mean a descent to 8,000 feet will rectify with headlights and flashlights. the problem. Visual acuity may not be regained for over an • Position the aircraft at a part of the airfield where the hour. Thus, it is important to remember, altitude and fatigue least amount of lighting exists. have a profound effect on a pilot’s ability to see. 17-24