Evaluation of Economical Visual Approach Indicators
An Evaluation was conducted to determine the feasibility of a variety of "low-cost" visual approach slope techniques intended to aid pilots in establishing a suitable glide path prior to landing.
The techniques included three-color and two-color types. Assessing the suitability of the hardware was not essential to the evaluation. Emphasis was placed on determining photometric characteristics, effects of humidity, and temperature upon beam structure, and usefulness as seen in flight. They were compared in flight tests to a two-box abbreviated version of the U.S. Standard twelve - box Visual Approach Slope Indicator (VASI).
Except for the two-box VASI, (1) all could produce misleading and possibly hazardous information when condensation or ice formed on the glass face-plates and (2) none had useful daytime range. Due to lack of boldness of presentation, all three-color units were difficult to distinguish from runway edge and obstruction lighting.
It was recommended the (1) tri-color techniques not be approved for operational use, (2) any techniques which produces a false signal be excluded from the national airspace system, (3) investigations be continued to reduce cost of the Standard and Abbreviated VASI's and (4) criteria be adopted for Abbreviated VASI's
NA-67-13 (RD-67-50)
Author: D. Michael Brandewie