Aeromedical Factors

n o z ori h al u A ct Apparent horizon Figure 17-22. At night, the horizon may be hard to discern due to dark terrain and misleading light patterns on the ground. parallel to another’s course. To determine the direction of steep surrounding terrain, and a wide runway can produce the flight, pilots should observe aircraft lights and their relative illusion of being too low with a tendency to fly a higher-than- position to the horizon. If the intensity of the lights increases, normal approach. A set of regularly spaced lights along a road the aircraft is approaching; if the lights dim, the aircraft is or highway can appear to be runway lights. Pilots have even moving away. mistaken the lights on moving trains as runway or approach lights. Bright runway or approach lighting systems can create Size-Distance Illusion the illusion that the aircraft is closer to the runway, especially This illusion results from viewing a source of light that is where few lights illuminate the surrounding terrain. increasing or decreasing in luminance (brightness). Pilots may interpret the light as approaching or retreating. Prior to flying at night, it is best to learn and know the challenges of the area in which you are flying in. Study the Fascination (Fixation) area and know how to navigate your way through areas that may pose a problem at night. For example, many areas near This illusion occurs when pilots ignore orientation cues and water may be obscured by low lying clouds or fog. To help fix their attention on a goal or an object. Student pilots tend to deal with this type of situation, it is important to have a plan have this happen when they are concentrating on the aircraft before you leave the ground. In the daytime, fly the routes instruments or attempting to land. They become fixated on and passes that you will be flying at night and determine the one task and forget to look at what is going on around them. minimum altitude you are willing to use at night. If weather At night, this can be especially dangerous because aircraft prevents you from maintaining the altitude that you planned, ground-closure rates are difficult to determine, and there may make a decision early to turn 180° and land at an alternate be minimal time to correct the situation. airport with better weather conditions. Always consider safer alternatives rather than hope things will work out by Flicker Vertigo taking a chance. A light flickering at a rate between 4 and 20 cycles per second can produce unpleasant and dangerous reactions. Such Pilots who fly at night should strongly consider oxygen conditions as nausea, vomiting, and vertigo may occur. On supplementation at altitudes and times not required by the rare occasions, convulsions and unconsciousness may also FAA, especially at night when critical judgment and hand-eye occur. Proper scanning techniques at night can prevent pilots coordination is necessary (e.g., IFR) or if he/she is a smoker from getting flicker vertigo. or not perfectly healthy. Night Landing Illusions Enhanced Night Vision Systems Landing illusions occur in many forms. Above featureless Synthetic Vision Systems (SVS) and Enhanced Flight Vision terrain at night, there is a natural tendency to fly a lower- Systems (EFVS) are two systems that can improve the safety than-normal approach. Elements that cause any type of of flight at night. The technology of both is evolving rapidly visual obscurities, such as rain, haze, or a dark runway and being used more and more. [Figure 17-23] environment, can also cause low approaches. Bright lights, 17-27