Flight Operations Briefing Notes
Human Performance
Visual Illusions Awareness
Introduction

Visual illusions take place when conditions modify the pilot’s perception of  the environment relative to his / her expectations.
Visual illusions may result in landing short of the runway, hard landing or runway overrun, but may also cause spatial disorientation and loss of control.
This Flight Operations Briefing Note provides an overview of:
Factors and conditions that may cause visual illusions;

How visual illusions affect the pilot’s perception of the airport / runway environment and runway; and,

How to reduce the effects of visual illusions by implementing related prevention strategies and lines-of-defense in training and line operation.

Statistical Data

30 % of approach-and-landing accidents occur during the conduct of visual approaches or during the visual segment of an instrument approach.
Visual approaches at night present a greater exposure because of reduced visual cues, increased likelihood of visual illusions and risk of spatial disorientation.
Low visibility and/or precipitations are a circumstantial factor in more than 70 % of approach-and-landing accidents, including those involving CFIT.
 
“ Visual ” Factors
 % of Events
 
Night time
 75 %
 
Low visibility
 70 %
 
IMC
 59 %
 
Darkness or twilight
 53 %
 
Non-ILS approach
 53 %
 
Precipitation (rain or snow)
 50 %
 
Visual approach
 30 %
 
Visual illusions or spatial disorientation
 21 %
 
Absence of : - letdown navaid - approach / runway lighting - VASI / PAPI
 21 %
 

 
( Source – Flight Safety Foundation 1998 – 2000 )
Table 1
“ Visual ” Factors in Approach-and-Landing Events
Visual Illusions – Factors and Conditions

The following factors and conditions affect the flight crew ability to accurately perceive the environment, resulting in visual illusions.
Airport Environment

Ground texture and features;

Off-airport light patterns such as brightly lighted parking lots or streets;

“Black hole” along the final approach flight path; and/or,

Uphill or downhill sloping terrain before the runway threshold or in the approach path environment.

Runway Environment

Runway dimensions (aspect ratio);

Runway uphill or downhill slope;

Terrain drop-off at the approach end of the runway;

Approach and runway lighting; and/or,

Runway condition (e.g., wet runway).
　
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