Optic flow and visual analysis of the base-to-final turn

In the spirit of other optic flow research, we address the problem of how a pilot turns an airplane into alignment with a runway, a maneuver that is one of the more challenging phases of visually controlled flight. In earlier work, Loomis and Beall (1992) proposed a rule for turning an aircraft into alignment: Turn the aircraft in such a way as to hold constant the rate of change of splay (the angle the projected runway makes with respect to the vertical). The experiment presented in this article was a psychophysical test of this rule. We compared day and night landing approaches as our experimental manipulation; we were interested in any role that ground texture might play in the spatial judgment involved in performing the landing approach. Three pilots varying in flight experience performed multiple approaches in a light aircraft for a total of 26 day and 25 night approaches. The three-dimensional trajectories of the aircraft were measured using differential global positioning system data. From these trajectories we computed a variety of motion variables (e.g., turn rate) and two optic flow variables (splay and splay rate). The similar performance of day and night approaches suggests that the pilots were using optic flow variables that were invariant with changes in the visibility of ground texture. A computer model was developed based on the optic flow rule and estimates of human visual processing thresholds. We conclude that the model gives a good description of pilot performance as tested in our experiment and may help to illuminate the cause of a class of airplane accidents during the common landing phase.