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The date was December 4, 1965. Two planes collided because one pilot suffered an optical illusion, an upslope effect caused by cloud tops, that made him believe they were on a collision course.  

His evasive climb inevitably steered them directly toward the other plane, causing them to clip each other.  

Though both damaged planes managed to make their incredible emergency landings, 4 people of the 112 occupants tragically died.  

Optical and sensory illusions are common in flight.  It happens when visual references to the horizon or ground are lost, obscured, or distorted.

Types of optical illusions*

False horizon:  

A pilot mistakes a slanted cloud layer, a geometric line of ground lights, or a starry sky meeting a dark shoreline for the actual horizon.

The Black Hole Approach:  

When landing at night over dark, featureless terrain or water with nothing but the runway lights visible. Without peripheral depth cues, pilots feel they are higher than they actually are, causing them to fly a dangerously low, shallow approach.

Runway Width & Slope Illusions:  

Narrower-than-usual runways make a pilot feel too high, causing them to fly a dangerously low approach.

Upsloping runways or upsloping terrain create the same "too high" illusion, prompting a premature descent.

Autokinesis:  

When staring at a single, stationary dim light (like a distant star or ground light) against a dark background for several seconds, the light will appear to randomly move or drift.  

A pilot might mistakenly try to align or "follow" this moving light.

Atmospheric Distortions (Haze and Rain):  

Rain on the windscreen refracts light and lowers the horizon visually, making the pilot feel higher than they are.  

Atmospheric haze makes the runway appear much farther away and higher up than it actually is.

Vestibular & Somatosensory Illusions (The Inner Ear)*

When visual references vanish (like flying inside a cloud), the brain relies on the inner ear, which is easily fooled by forces of acceleration and turning.

The Leans: 

The most common illusion in flight. If an aircraft enters a slow, gradual turn, the inner ear fluid doesn't move, so the pilot thinks they are flying straight. 

When they look at their instruments and correct back to level flight, their body strongly feels like the plane is banking heavily in the opposite direction, causing them to lean in the cockpit.

Somatogravic Illusion: 

Rapid forward acceleration (like a jet takeoff or a go-around) stimulates the inner ear in a way that feels exactly like the aircraft is pitching straight up into a steep climb. 

If the pilot reacts to this sensation instead of trusting their instruments, they will violently push the nose down into a catastrophic dive.

The Coriolis Illusion: 

Considered one of the deadliest illusions. It occurs when a pilot moves their head rapidly (like looking down to grab a chart) while the aircraft is in a prolonged constant turn. 

This activates multiple fluid canals in the inner ear simultaneously, creating an overwhelming, sickening sensation that the aircraft is tumbling, rolling, and spinning on an entirely different axis.

Graveyard Spiral: 

A pilot in a prolonged turn stops feeling the turn. When trying to level the wings, they feel like they’ve entered a turn in the opposite direction and will pull back on the yoke to stop a perceived descent. 

This actually tightens the spiral, causing the plane to lose altitude rapidly while the pilot believes they are climbing.

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The only way to defend against optical and sensory illusions is to ignore their physical sensations and trust the aircraft's flight instruments, which feels completely counterintuitive.

The point is that much of our broad-scope interactions are counterintuitive, and if you do not rely on the instruments of intelligence, knowledge, and proven economic, scientific, physical, and metaphysical laws, then the likely result would be catastrophic, tragic, and deadly.  

We cannot rely only on our instincts, or we will fall prey to false horizons and idols with grandiose illusions of grandeur, tripping on power along unsustainable paths of ruination and destruction.

*Referenced from Google AI search:  What kind of optical and sensory illusions in flight.

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