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8 Optical Illusions Every Pilot Should Understand

Optical illusions can significantly affect your ability to fly safely. Here's what every pilot should be prepared to handle...

1) Runway Width

A narrower-than-usual runway can create an illusion that the aircraft is higher than it actually is, leading to a lower approach. A wider-than-usual runway can create an illusion that the aircraft is lower than it actually is, leading to a higher approach.

2) Runway And Terrain Slope

A downsloping runway can create the illusion that the aircraft is lower than it actually is, leading to a higher approach. An upsloping runway can create the illusion that the aircraft is higher than it actually is, leading to a lower approach. The same is true for flying around sloping terrain.

Boldmethod

3) Featureless Terrain

Flying an overwater approach or an approach over darkened areas creates the illusion that the aircraft is at a higher altitude than it actually is. A great example of this is the "black hole" approach, causing pilots to fly a lower than normal final approach.

Simon Blakesley / Airliners.net

4) Water Refraction

Rain on the windscreen can create the illusion that you're flying at a higher altitude due to the horizon appearing lower than it is. This can result in pilots flying lower than normal on final approach.

Swayne Martin

5) Haze

According to the FAA, "atmospheric haze can create an illusion of being at a greater distance and height from the runway. As a result, the pilot will have a tendency to be low on the approach. Conversely, extremely clear air (clear bright conditions of a high altitude airport) can give the pilot the illusion of being closer than he or she actually is, resulting in a high approach, which may result in an overshoot or go around."

The diffusion of light due to water particles on the windshield can adversely affect depth perception. The lights and terrain features you normally use to judge height above the runway during landing are less effective.

Swayne Martin

6) Fog

Pilots who inadvertently enter fog or a cloud may feel like they've suddenly pitched up. Pilots who do not recognize this illusion may suddenly steepen the approach. Trust your instruments!

GolfCharlie232

7) Ground Lighting

Long, straight lights from something like a roadway might look like a runway in low light conditions. Bright runway lights may create the illusion that you're closer to the runway than you are. When this happens, pilots fly a higher than normal approach and flare.

Boldmethod

8) Flat Light

It's a normal winter day in the USA, with snow-covered fields and an overcast sky. It's not hazy at all; in fact, the visibility is crystal clear at well over 50 miles. You fly a short cross-country flight to visit relatives for the Holidays. Without realizing it, you descend closer and closer to the ground below, until suddenly, your aircraft impacts a snow-covered field at cruise speed.

The insidious nature of flat light is the real risk. Thinking they can see the ground, VFR pilots tend to rely on outside references to judge aircraft attitude. Normally, this is perfectly safe when flying VFR. But as visual references are slowly lost, the distinction between the ground, horizon, and sky becomes unclear.

NTSB

Have you experienced any of these illusions? Tell us about your experience in the comments below.

Swayne Martin

Swayne is an editor at Boldmethod, certified flight instructor, and an Embraer 145 First Officer for a regional airline. He graduated as an aviation major from the University of North Dakota in 2018, holds a PIC Type Rating for Cessna Citation Jets (CE-525), and is a former pilot for Mokulele Airlines. He's the author of articles, quizzes and lists on Boldmethod every week. You can reach Swayne at swayne@boldmethod.com, and follow his flying adventures on his YouTube Channel.

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