Visual slant misperception and the 'black-hole' landing situation.

A theory is presented which explains the often quoted tendency for dangerously low approaches during night-landing situations. The two-dimensional information at the pilot's eye contains sufficient information for the visual system to estimate correctly the angle of slant of the runway relative to the approach path. An algorithm is developed which can perform this angle estimation. It is dependent upon perspective information being available a certain lateral distance out from the aimpoint, to either side of the runway edgelights. However, under 'black-hole' landing conditions this information is not available, and it is proposed that the visual system uses instead the only available information--namely the perspective gradient of the runway edgelights. An equation is developed which predicts what the perceived approach angle will be when this incorrect perspective is used. The predictions are in close agreement with existing experimental data.