Perceived orientation of a runway model in nonpilots during simulated night approaches to landing
Mertens, H.W.
Aviation Space and Environmental Medicine 49(3): 457-460
1978
ISSN/ISBN: 0095-6562 PMID: 637802 Document Number: 137418
Illusions due to reduced visual cues at night have long been cited as contributing to the dangerous tendency of pilots to fly too low during night landing approaches. The cue of motion parallax, a difference in rate of apparent movement of objects in the visual field, is frequently suggested as contributing to visual judgments of glide path but has not been systematically studied in relation to the night approach problem. The effect of varying levels of motion parallax from both radial and vertical motion on perception of the orientation of a runway relative to the ground was studied. Under simulated nighttime conditions (only runway and approach lighting were visible), 16 nonpilots adjusted the apparent slant of a model runway to make it appear horizontal as the model moved toward them along a 3.degree. approach path from a simulated distance of 4.33 to 1.33 nautical miles. Simulated approach speeds of 62 and 125 kn were used. The rate at which the model rotated during slant adjustments varied between 5.degree. and 30.degree./min. The adjusted slant of the runway model with respect to the approach path (generated approach angle) was the dependent variable. The average generated approach angle for 256 trials was 0.5.degree. This consistent and large deviation from 3.degree., which would represent accurate perception, indicated the presence of strong illusions, was in agreement, with the documented tendency of pilots to fly low approaches at night and was explained in terms of the equidistance tendency and/or errors in perceiving the direction of the model in the visual field. Motion parallax in the runway image was neither a reliable nor an effective cue for the safe judgment of glide path at distances greater than 1.33 miles.