whiteout An atmospheric optical phenomenon of snow-covered regions in which the observer appears to be engulfed in a uniformly white glow. Shadows, the horizon, and clouds are not discernible; depth perception and the sense of orientation are lost; and only very dark, nearby objects can be seen. Whiteout occurs over an unbroken snow cover and beneath a uniformly overcast sky when, with the aid of the snowblink effect, the light from the sky is about equal to that from the snow surface. Blowing snow may be an additional cause. Fr: voile blanc
wide area augmentation system
U.S. and Canada: The augmentation to global positioning system (GPS) to meet en route and terminal navigation, non-precision approach and precision approach CAT I accuracy, integrity, continuity and availability requirements. The ground system comprises a sparse network of ground reference stations and a master station linked by terrestrial communications. In the space system, an uplink from the master station provides information to geostationary satellites that transmit an integrity message, corrections and a GPS ranging signal to user avionics.
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abbreviation: WAAS
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see also: local area augmentation system (LAAS)
Fr: système de renforcement à couverture étendue
“Wilco” An expression used in radiocommunication meaning “I understand your message and will comply with it.” Note: Abbreviation for “Will comply.” Fr: . Wilco .
wind cone Other expression for: wind direction indicator
wind direction indicator
(1) An indicator that is in the form of a truncated cone made of fabric and that is not less than 12 ft long and, at the larger end, not less than 3 ft in diameter, so constructed as to give a clear indication of the direction of surface wind and a general indication of wind speed.
. also called: wind cone, wind sleeve and windsock
Fr: indicateur de direction du vent
(2) An actuated device for indicating visually to aircraft the direction of surface wind.
Fr: indicateur de direction du vent
wind shear A change in wind speed and/or wind direction in a short distance. It can exist in a horizontal or vertical direction and occasionally in both.
. abbreviation: WS
Fr: cisaillement du vent
wind sleeve Other expression for: wind direction indicator
windsock Other expression for: wind direction indicator
wing-tip vortex A circular pattern of air current created by the movement of an airfoil through the air when the airfoil is generating lift. As an airfoil moves through the atmosphere in sustained flight, an area of high pressure is created beneath it and an area of low pressure is created above it. The air flowing from the high-pressure area to the low-pressure area around and about the tips of the airfoil tends to roll up into two rapidly rotating vortices, cylindrical in shape. These vortices are the predominant parts of aircraft wake turbulence and their rotational force is dependent upon the wing loading, gross weight, and speed of the generating aircraft. The vortices from medium to heavy aircraft can be of extremely high velocity and hazardous to smaller aircraft. Fr: tourbillon en bout d’aile
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