W Whiskey

WA (AIRMET) - see AIRMET

WAC (World Aeronautical Charts) - These charts provide a standard series of aeronautical charts covering land areas of the world at a size and scale convenient for navigation by moderate speed aircraft. Topographic information includes cities and towns, principle roads, railroads, distinctive landmarks, drainage and relief. Aeronautical information includes visual and radio aids to navigation, airports, controlled airspace, restricted areas, obstructions, and pertinent data.

wake - Tumultuous currents of air trailing from the side and behind an aircraft in flight. Generally, the heavier the aircraft and the more concave the wing surfaces, the greater the wake turbulence. Wake turbulence is a threat to all aircraft flying behind other aircraft. The term includes vortices, thrust stream turbulence, jet blast, propeller wash, and rotor wash.

waypoint - A predetermined geographical position used for route/instrument approach definition, or progress reporting purposes, that is defined relative to a VORTAC station or in terms as latitude/longitude coordinates.

weather - The state of the atmosphere at a specific time and with respect to its effect on life and human activities. It is the short term variations of the atmosphere, as opposed to the long term, or climatic, changes. It is often referred to in terms of brightness, cloudiness, humidity, precipitation, temperature, visibility, and wind.

weather advisories - Updated weather reports available to pilots during the en route phase of a flight.

Weather Depiction Chart - A simplified version of a surface weather chart used for flight planning and determination of general weather conditions. It also helps pilots to quickly locate areas of adverse weather. This report is issued every 3 hours.

weather forecast - A computer generated "best guess" as to what the weather will be at a particular time in a particular area.

weather report - A report of the state of the atmosphere at a specific time and with respect to its effect on life and human activities. It is the short term variations of the atmosphere, as opposed to the long term, or climatic, changes. It is often referred to in terms of brightness, cloudiness, humidity, precipitation, temperature, visibility, and wind.

weight - The force of gravity acting on an object. The weight force pulls an aircraft toward the Earth and must be overcome by a combination of lift and thrust.

Whiskey - Designator for the letter "W" in the International Phonetic Alphabet.

wind - Air in motion relative to the surface of the Earth.

wind direction - The direction from which the wind is blowing. For example, an easterly wind is blowing from the east, not toward the east. It is reported with reference to true north, or 360 degrees on the compass, and expressed to the nearest 10 degrees, or to one of the 16 points of the compass (N, NE, WNW, etc.).

wind shear - A sudden drastic change in wind speed, wind direction or both that may occur in the vertical or horizontal plane, resulting in a tearing or shearing affect.

wind shift - The term applied to a change in wind direction of 45 degrees or more, which takes place in less than 15 minutes. It may the result of a frontal passage, from katabatic winds, sea breezes, or thunderstorms, and in some instances, the change may be gradual or abrupt.

wind speed - The rate of the motion of the air on a unit of time. It can be measured in a number of ways. In observing, it is measured in knots, or nautical miles per hour.

wind tunnel - Tubular structure or passages in which high-speed movements of air or other gases are produced. Objects such as engines, aircraft, airfoils and rockets are placed inside the wind tunnel so researchers can investigate the airflow around them and the aerodynamic forces acting upon them.

wind tunnel testing - A Tool of Aeronautics that involves placing a model of an aircraft or part of an aircraft into a wind tunnel and using instruments to gather data while air is blown by the model. Wind tunnel testing is used to investigate and accurately describe the effects of airflow on an aircraft or part of an aircraft.

wing - A part of an airplane that is attached to the fuselage. Wings are shaped like airfoils and are used to provide lift for the airplane. There are four basic types of wings: straight, sweep, delta and variable sweep.

wingspan - On a fixed-wing aircraft, the span or straight-line distance between one wingtip and the other, including any projecting ailerons. (The term "wingspan" always refers to the tip-to-tip span of an entire wing; never to a wing half on just one side of a fuselage.)

wingtip vortices - Circular patterns of air created by the movement of an airfoil through the air when generating lift. As an airfoil moves through the atmosphere in sustained flight, an area of 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 most 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.

WS (SIGMET) - Standing for significant meteorological information, it is a weather report issued for hazardous weather which is considered significant to all aircraft. e.g.: severe icing, severe and extreme turbulence, and duststorms, sandstorms or volcanic ash lowering visibility to less than 3 miles. See SIGMET

WST (Convective SIGMET) - In-flight weather advisory concerning tornadoes, lines of thunderstorms, embedded thunderstorms, areas of thunderstorms, and/or hail greater than or equal to 3/4 inch in diameter.

WW (Severe Weather Watch Bulletin) - An aviation weather report that identifies areas of possible severe thunderstorms or tornadoes.