Optical Illusions

Optical Illusions

Vision is the primary sense used by pilots to maintain situational awareness and ensure safe flight operations. However, visual illusions can occur under certain atmospheric and environmental conditions, especially during landing. Understanding these illusions and knowing how to mitigate their effects is crucial for pilots to maintain control and execute safe landings.

Types of Optical Illusions

Runway Width Illusion [Figure 1]

A narrower-than-usual runway can create the illusion that the aircraft is higher than it actually is. Pilots may respond by flying a lower approach, increasing the risk of landing short or striking obstacles. Conversely, a wider-than-usual runway can cause the illusion of being lower than actual, leading to a higher approach and the possibility of a hard landing or overshooting the runway.

Runway and Terrain Slope Illusion [Figure 1]

An upsloping runway or terrain can give the false impression that the aircraft is higher than it is, leading the pilot to fly a lower-than-intended approach. A downsloping runway or terrain has the opposite effect, causing the pilot to fly a higher approach, which may result in a hard landing or a go-around.

Figure 1 Runway illusions (Pilots Handbook of Aeronautical Knowledge)

Featureless Terrain Illusion

When flying over a body of water, snow-covered ground, or dark terrain with no visible features, pilots may experience the "black hole approach" illusion. This makes the aircraft appear higher than it actually is, leading to a lower approach and an increased risk of landing short.

Water Refraction

Rain on the windscreen distorts the view of the runway and surrounding environment. This can create the illusion of a lower horizon, causing pilots to believe they are higher than they actually are and resulting in a lower approach.

Haze

Atmospheric haze can make the runway appear further away, leading pilots to fly lower approaches. In contrast, exceptionally clear air can create the illusion of proximity, prompting a higher-than-normal approach and the risk of overshooting the runway.

Fog

Entering fog can create a visual illusion of pitching up. Pilots who are unaware of this may respond by steepening the descent, potentially leading to a dangerously rapid approach.

Ground Lighting Illusions

Pilots may mistake road lights, trains, or other ground lighting for runway and approach lights, leading to disorientation and possible misalignment. Additionally, bright runway and approach lights can make the runway appear closer than it is, causing a pilot to fly a higher approach.

Preventing and Mitigating Optical Illusions

To prevent the effects of optical illusions, pilots can follow these best practices:

• Anticipate visual illusions during approaches to unfamiliar airports, particularly at night or in adverse weather conditions.

• Consult airport diagrams and the Chart Supplement U.S. for information on runway slope, terrain, and lighting.

• Make frequent reference to the altimeter to ensure accurate altitude awareness.

• Conduct an aerial visual inspection of unfamiliar airports when possible.

• Use visual aids like Visual Approach Slope Indicator (VASI) or Precision Approach Path Indicator (PAPI) systems for reliable glide path guidance.

• Rely on the visual descent point (VDP) during nonprecision instrument approaches.

• Stay vigilant and minimize distractions, particularly during emergencies or abnormal flight conditions.

• Maintain proficiency in landing procedures through regular practice and simulator training.

Optical illusions pose a significant risk to flight safety, especially during landing. By recognizing the conditions that may produce these illusions and employing proactive mitigation strategies, pilots can reduce the likelihood of landing errors. Continuous training, effective use of instruments, and sound decision-making are essential for navigating visual illusions safely.