Visual spatial disorientation: revisiting the black hole illusion.

Spatial disorientation (SD) is often cited as a contributor to aviation accidents. A specific type of visual SD, the "black-hole illusion" (BHI), occurs on approach to landing at night when the outside view lacks cues to terrain around the lighted runway. Pilots too often confidently proceed with a visual approach despite the impoverished visual conditions; the BHI then causes them to experience glide path overestimation (GPO) so that they initiate an inappropriately steep descent. The result is a shallow approach that lies below the correct glide path for obstacle clearance. This review explores the origins of the BHI and describes several mishaps involving it. Nine possible reasons for pilot misperception leading to GPO are described: constancy of apparent size-shape-depth; conflict between familiar and relative size; overestimation of visual angles in the medial extent; deficient terrain orientation cues; lack of distance cues; disparity between optical and geographical slant; perception of approach lighting systems; tendency toward equidistance; and misperception of slant. Mishaps involving visual SD are not pilot error, but demonstrate a perceptual limitation, and more needs to be learned regarding when and where the BHI may occur. It is already clear, however, pilots should be taught that confidence in their visual capabilities during impoverished viewing conditions greatly exceed their perceptual abilities. With the increase in night flying in military and civilian settings, reduction in landing mishaps will depend in part on inclusion of visual SD scenarios in initial and refresher pilot training with presentation of BHI scenarios in annual flight simulator sessions.