Evaluation of Runway Lighting Systems For Effectiveness in Dense Fog

Tests of runway lighting systems in dense fog show that an intensity of 200 to 300 cp, now in general use for centerline lights at U.S. airports, is not high enough for effective guidance in a fog density of 1200-ft visual range, day or night. These tests also indicate that in daytime, with a 1200-ft visual range runway marking is considerably useful to pilots as a supplement to runway lighting. In addition, on the basis of pilots' reactions, the present U.S. standard pattern
(3:3:3) for touchdown-zone and centerline lights was found to be more effective than either of two other patterns (3:2:1 and 7:3:1) evaluated. Pilots also preferred a modified version of the present U. S. standard approach-light system.

The tests were performed in a specially designed facility using artificially produced fog and a linear scale reduction factor of 1/10. Evaluations were made from pilot observations, as well
as photometric-measurement and photographic techniques.

The test facilities and methods are described, the test results are presented, and some of the influencing factors, such as background brightness and cockpit cutoff angle, are discussed. In addition, a number of recommendations are made with regard to intensities and photometric distributions for runway lights, and with respect to changes in the present u. s. standard approach light system.