• Select approach and departure routes that avoid  highways and residential areas where illumination  can impair night vision.  Night flight can be more fatiguing and stressful than day  flight, and many self- imposed stressors can limit night vision.  Pilots can control this type of stress by knowing the factors  that can cause self-imposed stressors. Some of these factors  are listed in the following paragraphs.  [Figure 17-20]  Drugs can seriously degrade visual acuity during the day and  especially at night. Pilots who become ill should consult an  aviation medical examiner (AME) or flight surgeon as to  which drugs are appropriate to take while flying.  affects peripheral vision and dark adaptation. The results  are the same as those for hypoxia caused by high altitude.  Smoking 3 cigarettes in rapid succession or 20 to 30 cigarettes  within a 24-hour period may saturate from 8 to 10 percent  of the capacity of hemoglobin. Smokers lose 20 percent of  their night vision capability at sea level, which is equal to a  physiological altitude of 5,000 feet.  Pilots who become fatigued during a night flight will not be  mentally alert and will respond more slowly to situations  requiring immediate action. Exhausted pilots tend to  concentrate on one aspect of a situation without considering  the total requirement. Their performance may become a  safety hazard depending on the degree of fatigue and instead  of using proper scanning techniques may get fixated on the  instruments or stare off rather than multitask.  To overcome poor physical conditioning, pilots should  participate in regular exercise programs. People who are  physically fit become less fatigued during flight and have  better night scanning efficiency. However, too much exercise  in a given day may leave crew members too fatigued for  night flying.  Missing or postponing meals can cause low blood sugar,  which impairs night flight performance. Low blood sugar  levels may result in stomach contractions, distraction,  breakdown in habit pattern, and a shortened attention span.  Likewise, an insufficient consumption of vitamin A may  also impair night vision. Foods high in vitamin A include  eggs, butter, cheese, liver, apricots, peaches, carrots, squash,  spinach, peas, and most types of greens. High quantities of  vitamin A do not increase night vision but a lack of vitamin  A certainly impairs it.  Knowledge of the mechanisms and cues affecting distance  estimation and depth perception assist pilots in judging  distances at night. These cues may be monocular or binocular.  The monocular cues that aid in distance estimation and depth  perception include motion parallax, geometric perspective,  retinal image size, and aerial perspective.  Alcohol is a sedative and its use impairs both coordination  and judgment. As a result, pilots who are impaired by alcohol  fail to apply the proper techniques of night vision. They are  likely to stare at objects and to neglect scanning techniques.  The amount of alcohol consumed determines the degree to  which night vision is affected. The effects of alcohol are long  lasting and the residual effects of alcohol can also impair  visual scanning efficiency.  Motion parallax refers to the apparent motion of stationary  objects as viewed by an observer moving across the  landscape. When the pilot or crewmember looks outside the  aircraft perpendicular to the direction of travel, near objects  appear to move backward, past, or opposite the path of  motion; far objects seem to move in the direction of motion  or remain fixed. The rate of apparent movement depends on  the distance the observer is from the object.  Of all the self-imposed stressors, cigarette smoking most  decreases visual sensitivity at night. Smoking significantly  increases the amount of carbon monoxide carried by the  hemoglobin in red blood cells. This reduces the blood’s  capacity to combine with oxygen, so less oxygen is carried  in the blood. Hypoxia caused by carbon monoxide poisoning  17-25  Motion Parallax  Distance Estimation and Depth Perception  Tobacco  Alcohol  Poor Physical Conditioning  Hypoglycemia and Nutritional Deficiency  Exhaustion  Drugs  Self-Imposed Stress  Figure 17-20.  Self-imposed stress.  HYPOGL Y CEMIA ALCOHOL TOBACCO POOR PHYSICAL  CONDITION EXHA USTION DRUGS NUTRITIONAL  DEFICIENCY