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This technical note describes a research effort that was accomplished to correct a safety deficiency with a Visual Approach Slope Indicator (VASI) system at the Pearson Field Airpark in Vancouver, Washington. During a recent inspection flight, the VASI system was found to be emitting signals that could potentially draw an approaching aircraft dangerously close to an obstruction near the final approach path. As a result, the system was shutdown. The VASI system had baffles previously installed on the inside and on the front opening of the unit that were intended to limit the emission of light in the direction of the obstruction. The baffles were found to have very comparable opening widths in all units of the system, which allowed the signal from some units to be visible within a very close proximity to an obstruction. Typically, each opening requires a different width to provide proper signal blocking at the specific location of the obstruction. The Federal Aviation Administration Northwest-Mountain Region, Navigational Surveillance Weather Systems Team requested the Airport Technology Research and Development Branch’s assistance in correcting the misaligned baffles so that the VASI system could be restored to operation.
Engineers from the Airport Technology Research and Development Branch visited the site to analyze the problem; collect data on the geometry of the obstruction, the baffles, and the general layout of the airport; and install and test the new baffles to make sure they operate properly. Engineers designed, constructed, and installed aluminum baffles that blocked the signal from the obstruction area, and provided a 2 degree margin of safety between the obstruction and the visible signal of the VASI.
Ground and flight evaluations conducted by the Airport Technology Research and Development Branch verified that the installed baffles had eliminated the hazard by preventing a usable VASI signal from being seen near the obstruction.
DOT/FAA/AR-TN07/12
Author: James W. Patterson Jr.
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