Visual illusions during flight can significantly impact a pilot’s perception of altitude, position, and speed, leading to incorrect actions and potential hazards. Being aware of these illusions and their causes is essential for safe approach and landing. One must understand the effect of visual illusion on approach path as well as flare.
In most commercial flights, the impact of varying approach path perceptions can be mitigated through the use of vertical guidance systems. However, the flare maneuver during landing is often still affected by these visual illusions.
Sloping Terrain Towards or Away from the Runway
When approaching a runway with “sloping terrain toward the runway”, pilots may experience an illusion of being too low. The downward slope of the terrain can create a false perception of descending too quickly. In response, pilots may overcompensate by flying a higher-than-normal approach, which could lead to landing beyond the intended touchdown zone.
In contrast, “sloping terrain away from the runway” can give the opposite illusion, where the pilot feels too high and might fly a lower approach than necessary. This can increase the risk of landing short of the runway.
Sloping Runway
A “runway with an upslope” can give the illusion that the aircraft is higher than it actually is. This can lead to a low approach and potentially a hard landing (low flare). Conversely, a “down sloping runway” can make the aircraft seem lower than it is, prompting the pilot to fly too high on approach. This can also cause an issue of high flare.
Runway Width
The width of the runway also plays a significant role in how a pilot perceives the aircraft’s distance. A “wider-than-usual runway” will appear closer than it is, potentially causing the pilot to fly too high on approach. On the other hand, a “narrower-than usual runway” will look farther away, leading to a lower approach than intended.
Runway Brightness
Bright runway lights can create the illusion that the runway is closer than it is (can lead to a high flare), while dim lights may give the impression that the runway is farther away (can lead to a low flare). This can be especially problematic at night or during low-visibility conditions.
The Black Hole Effect
The “black hole effect” is one of the most dangerous visual illusions pilots face, particularly during night landings over unlit terrain, water, or featureless areas such as deserts. When approaching a lighted runway with no visible horizon, the surrounding darkness can make the pilot feel as though they are on the correct glide path when, in fact, they are descending too steeply. This illusion can lead to a controlled flight into terrain (CFIT) if the pilot does not realize the mistake in time.
Black hole effect causes pilot to perceive that he/she is high on approach.
The most effective way to avoid the black hole illusion is to avoid long, straight-in approaches at night over unlit terrain. Always follow VASI or PAPI indications to stay on the proper glide path. Be aware that even with knowledge of the illusion, pilots may still feel a strong urge to believe their false visual impressions. Relying on instruments is critical. Black hole illusion disappears within 2 to 3 miles of an airport.
Visual Illusions in Fog or Low Visibility
During approaches in shallow fog or low-visibility conditions, the visual reference of the runway or approach lights may be reduced. This can create the illusion that the airplane is higher than it is, causing the pilot to overcorrect with a steeper descent. This mis-judgment could result in a high rate of descent and a hard landing.
Similarly, haze reduces the visibility and can make the runway appear farther away, leading to a low approach.
Runway Contrast Illusion
Problems in depth perception can arise when the color of the runway blends with the surrounding terrain. For example, a snow-covered runway or a water landing on a glassy sea can make it difficult to accurately judge distance and altitude.
Windshield Moisture and Visibility Issues
Moisture on the windshield can interfere with visibility and create off-glide path illusions. Depending on the airplane and the pattern of moisture on the windshield, the pilot may perceive that the aircraft is above or below the glide path, or off-center relative to the runway.
Visual illusions can pose a serious threat during flight, especially during landing approaches. While pilots may be aware of the possibility of these illusions, it can still be challenging to overcome the overwhelming visual cues that suggest something is amiss. Knowledge, preparation, and reliance on instruments are the best ways to safely navigate and land despite these deceptive situations. By understanding the common types of visual illusions and how to mitigate their effects, pilots can reduce the risk of accidents and ensure a safer flight experience.
