When it comes to night vision, we aren’t very good because we weren’t built for it. In fact, if it weren’t for rods, we wouldn’t be able to see anything in the dark. Rods (photoreceptor cells scattered across the retina) do well in peripheral vision and are much more sensitive to light which makes them a necessity for our nighttime flying. But rods can’t process color which is why our night vision isn’t very colorful.
Given that we rely so heavily on our eyes providing our brain with correct information, night flying leaves us susceptible to these common night illusions:
Night blind spot – because the rods excel in peripheral vision, off-center viewing provides the only means of seeing dim objects in the dark. If fact, if you choose to look directly at an object for more than a few seconds at night, the object could disappear completely from your vision which is known at the night blind spot.
False Horizon Flying – at night under clear skies with ground lights below can result in situations where it is difficult to distinguish the ground lights from the stars. A dark scene spread with ground lights and stars, and certain geometric patterns of ground lights can provide inaccurate visual information, making it difficult to align the aircraft correctly with the actual horizon. A visible sloping cloud formation can also affect a pilot’s sense of the horizon.
Autokinesis – In the dark, a stationary light will appear to move about when stared at for many seconds. The disoriented pilot could lose control of the aircraft in attempting to align it with the false movements of this light.
Featureless Terrain Illusion – A black-hole approach occurs when the landing is made from over water or non-lighted terrain where the runway lights are the only source of light. Without peripheral visual cues to help, orientation is difficult. The runway can seem out of position (down-sloping or up-sloping) and in the worst case, results in landing short of the runway.
Bright runway and approach lighting systems may create the illusion of being lower or having less distance to the runway. In this situation, the tendency is to fly a higher approach. Also, flying over terrain with only a few lights makes the runway recede or appear farther away. With this situation, the tendency is to fly a lower-than normal approach. If the runway has a city in the distance on higher terrain, the tendency is to fly a lower-than-normal approach. A good review of the airfield layout and boundaries before initiating any approach helps maintain a safe approach angle.
Ground Lighting Illusions – Lights along a straight path, such as a road or lights on moving trains, can be mistaken for runway and approach lights. Bright runway and approach lighting systems, especially where few lights illuminate the surrounding terrain, may create the illusion of less distance to the runway. The pilot who does not recognize this illusion will often fly a higher approach.
Illusions created by runway lights result in a variety of problems. Bright lights or bold colors advance the runway, making it appear closer. Night landings are further complicated by the difficulty of judging distance and the possibility of confusing approach and runway lights. For example, when a double row of approach lights joins the boundary lights of the runway, there can be confusion as to where the approach lights terminate and runway lights begin. Under certain conditions, approach lights can make the aircraft seem higher in a turn to final, than when its wings are level.
At a towered field, pilots may ask for lighting intensity to be changed and at many non-towered airports, the pilots may be able to adjust lighting intensities on the appropriate pilot-controlled lighting frequency.
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