TD 62 Flashcards
. What physiological effects do smoking 3 cigarettes in rapid succession or 20 to 30 cigarettes within 24 hours before a flight have on a smoker’s night vision and physiological altitude?
The resulting physiological effects at sea level are the same as flying at 5,000 feet but, more importantly, the individual loses about 20 percent of his or her night vision capability.
What is the difference between the night and day blind spot and how do we compensate for both?
Day Blind Spot 8-11. Since humans have two eyes, they view all images with binocular vision. Each eye compensates for the day blind spot in the optic disk of the opposite eye. The day blind spot covers an area of 5.5 to 7.5 degrees and is located about 15 degrees from the fovea, originating where the optic nerve attaches to the retina. The size of the day blind spot is due to the optic nerve’s oval shape combined with its offset position where it attaches to the retina. No cones or rods are present at the attachment point. The day blind spot causes difficulty when individuals do not move their head or eyes but continue to look straight forward while an object is brought into the visual field. Figure 8-2 demonstrates the day blind spot.
NIGHT BLIND SPOT 8-16. The night blind spot (figure 8-6) should not be confused with the day blind spot. The night blind spot occurs when the fovea becomes inactive in low light conditions and involves an area from 5 to 10 degrees wide in the center of the visual field. An object viewed directly at night might not be seen due to the night blind spot; if the object is detected, it will fade away when stared at longer than 2 seconds. The size of the night blind spot increases as the distance between the eyes and object increases. Therefore, the night blind spot can hide larger objects as the distance between the observer and object increases. Figure 8-7 (page 8-6) illustrates this effect.
(TC 3-04.93)
- How can night blind spot and the negative effects of scotopic vision be overcome?
PERIPHERAL VISION 8-17. Stimulation of only rod cells (peripheral vision) is primary for viewing during scotopic vision. Crewmembers must use peripheral vision to overcome the effects of scotopic vision. Peripheral vision allows crewmembers to see dimly lit objects and maintain visual reference to moving objects.
- What is the CAUTION associated with the landing/search light?
Landing and searchlight have less than one foot ground clearance when extended. Use caution when taxiing over rough terrain when landing light and/or searchlight are extended.
- What is the off-center viewing technique?
OFF-CENTER VISION 8-47. There are no limitations to viewing an object with central vision during daylight. If this same technique is used at night, however, the viewer might not see the object due to the night blind spot that exists under low light illumination. To compensate for this limitation, crewmembers must use the off- center vision technique (figure 8-12). This technique requires crewmembers to view an object by looking 10 degrees above, below, or to either side rather than directly at the object. The eyes maintain visual contact with the object via peripheral vision.
What is the visual acuity of the human eye during the day, night, and under NVGs?
Day = 20/20 Night = 20/200 or less NVG = 100% Illumination 20/25 NVG = 0% illumination = 20/70
The average time required to gain the greatest sensitivity or adaptation to a dark environment is ________ minutes. When fully dark adapted the rod cells become up to _______ times more sensitive than at the start of the dark adaptation period
30-45
10,000
Describe how high and low flight altitudes affect terrain interpretation.
4-33. Changes in viewing angle and distance at which an aviator is viewing an object will change the apparent shape of that object. The ability to identify manmade or natural features progressively decreases as flight altitude increases. This condition is affected at all levels of ambient light. When flight altitude increases, contrast between features becomes less distinguishable and features tend to blend. As terrain definition becomes less distinct, detection from altitude becomes difficult.
Low Altitude 4-34. Terrain becomes more clearly defined and contrast is greater when an aviator flies closer to the ground. This allows manmade and natural features to be more easily recognized and permits increased navigational capability. However, the viewable area of a crewmember at low altitudes is smaller than at higher altitudes. With NOE/contour altitudes, that area is even smaller, sometimes requiring an aviator to reduce airspeed to permit more accurate terrain interpretation. Objects can also be identified at low altitudes by silhouetting them against the skyline.
