See wide area augmentation system.

Wake turbulence
Wingtip vortices that are created when an aircraft generates lift. When an aircraft generates lift, air spills over the wingtips from the high pressure areas below the wings to the low pressure areas above them. This flow
causes rapidly rotating whirlpools of air called wingtip vortices or wake turbulence.

Warm front
The boundary area formed when a warm air mass contacts and flows over a colder air mass. Warm fronts cause low ceilings and rain.

Warning Area
A warning area is airspace of defined dimensions extending from 3 nautical miles outward from the coast of the United States, that contains activity that may be hazardous to nonparticipating aircraft. The purpose of such warning area is to warn nonparticipating pilots of the potential danger. A warning area may be located over domestic or international waters or both.


Warning area
An area containing hazards to any aircraft not participating in the activities being conducted in the area. Warning areas may contain intensive military training, gunnery exercises, or special weapons testing.

See weather and radar processing.

Washout strut
The structural member attached to the leading edges which holds the tip twist for the wing at low or negative angles of attack.

The design of the WSC wing in which a wing is twisted so its angle of attack is less at the tip than at the root. Washout decreases the lift the wing produces at the tip to improve the stall characteristics of the wing. Also called twist.

Waste gate.
A controllable valve in the tailpipe of an aircraft reciprocating engine equipped with a turbocharger. The valve is controlled to vary the amount of exhaust gases forced through the turbocharger turbine.

Retractable control surfaces on the back of each float that can be extended downward into the water
to provide more directional control when taxiing on the surface. They are attached by cables and springs
to the air rudder and operated by the rudder pedals in the cockpit.

Water vapor.
Water present in the air while in its vapor form.
It is one of the most important of atmospheric constituents.

Wave length.
The distance between two wave crests or
wave troughs.

Wave window.
Special areas arranged by Letter of
Agreement (LOA) with the controlling ATC wherein gliders
may be allowed to fly under VFR in Class A Airspace at
certain times and to certain specified altitudes.

The distance between two adjacent maxima or minima of a periodic disturbance.

A predetermined geographical position used for route/instrument approach definition, progress reports, published VFR routes, visual reporting points or points for transitioning and/or circumnavigating controlled and/or special use airspace, that is defined relative to a VORTAC station or in terms of latitude/longitude coordinates.

See wind correction angle.

In aviation weather forecast practice, an expression of hazardous weather conditions not predicted in the area forecast, as they affect the operation of air traffic and as prepared by the NWS. (See AIRMET.) (See SIGMET.)

Weather and radar processor (WARP).
A device that provides real-time, accurate, predictive, and strategic weather information presented in an integrated manner in the National Airspace System (NAS).

Weather briefing
Means for pilots to gather information vital to the nature of the flight from a flight service station specialist.

Weather depiction chart.
Details surface conditions as derived from METAR and other surface observations.

The tendency to point into the wind. 

The tendency of an aircraft to turn until it points into the wind.

Determine neutral buoyancy of a gas balloon or airship by taking weight off at launch.


A measure of the heaviness of an object. One of the four main forces acting on an aircraft. The force by which a body is attracted downward toward the center of the Earth (or another celestial body) by gravity. Weight is equal to the mass of the body times the local value of gravitational acceleration.

One of the four main forces acting on a rotorcraft. Equivalent to the actual weight of the rotorcraft. It acts downward toward the center of the earth.

Acting vertically through the glider’s center of gravity, weight opposes lift.

The force exerted by an aircraft from the pull of gravity.

Weight-Shift Control Aircraft
Powered aircraft with a framed pivoting wing and a fuselage controllable only in pitch and roll by the pilot’s ability to change the aircraft’s
center of gravity with respect to the wing. Flight control of the aircraft depends on the wing’s ability to flexibly deform rather than the use of control surfaces.

Weight-Shift Control-Land (WSCL)
WSC that takes off and lands on land. This can be wheels or ski equipped.

Weight-Shift Control-Sea (WSCS)
WSC that takes of the water. This can be pontoons or a boat configuration.

a. In conjunction with ATC instructions, gives the pilot the latitude to delay compliance until a condition or event has been reconciled. Unlike pilot discretion, when instructions are prefaced when able, the pilot is expected to seek the first opportunity to comply. b. In conjunction with a weather deviation clearance, requires the pilot to determine when he/she is clear of weather, then execute ATC instructions. c. Once a maneuver has been initiated, the pilot is expected to continue until the specifications of the instructions have been met. When able, should not be used when expeditious compliance is required.

Whip stall
A pitch attitude that is too high for a WSC, at which the tips would stall from flying outside the WSC limitations or flying in extreme/severe turbulence.

The WAAS is a satellite navigation system consisting of the equipment and software which augments the GPS Standard Positioning Service (SPS). The WAAS provides enhanced integrity, accuracy, availability, and continuity over and above GPS SPS. The differential correction function provides improved accuracy required for precision approach.

I have received your message, understand it, and will comply with it.

Wind correction angle (WCA).
The angle between the desired track and the heading of the aircraft necessary to keep the aircraft tracking over the desired track.

Wind direction indicators
Indicators that include a wind sock, wind tee, or tetrahedron. Visual reference will determine wind direction and runway in use.

Wind direction indicators.
Indicators that include a wind sock, wind tee, or tetrahedron. Visual reference will determine wind direction and runway in use.

Wind direction.
The direction the wind is coming from.

Wind drift correction
Correction applied to the heading of the aircraft necessary to keep the aircraft tracking over a desired track. Also called the wind correction angle or crab angle.

A display that presents the latest forecasted wind data overlaid on a map of the ARTCC area. Wind data is automatically entered and updated periodically by transmissions from the National Weather Service. Winds at specific altitudes, along with temperatures and air pressure can be viewed.

A change in wind speed and/or wind direction in a short distance resulting in a tearing or shearing effect. It can exist in a horizontal or vertical direction and occasionally in both. WIND SHEAR ESCAPE An unplanned abortive maneuver initiated by the pilot in command (PIC) as a result of onboard cockpit systems. Wind shear escapes are characterized by maximum thrust climbs in the low altitude terminal environment until wind shear conditions are no longer detected.

Wind shear
A change in direction and/or speed of the wind. a. Horizontal wind shear-for the purposes of this AC, the change in direction and/or speed of the wind at constant altitude. b. Vertical wind shear-for the purposes of this AC, the change in direction and/or speed of the wind with height.

Wind triangle.
Navigational calculation allowing
determination of true heading with a correction for
crosswinds on course.

Winds and temperature aloft forecast (FD).
A twice daily forecast that provides wind and temperature forecasts for
specific locations in the contiguous United States.

Upwind, or the upwind side of an object.

Wing area.
The total surface of the wing (in square feet), which includes control surfaces and may include wing area covered by the fuselage (main body of the airplane), and engine nacelles.

Stabilizer floats found near the wingtips of flying boats and single main float floatplanes to prevent the wingtips from contacting the water. Also called tip floats.

Wing keel
The WSC structural component in the longitudinal
center of the wing that connects the two leading edges
together at the nose and connects the carriage to the wing.

Wing loading
The amount of weight that a wing must support to provide lift.

Wing span.
The maximum distance from wingtip to wingtip.


Wing twist.
A design feature incorporated into some wings to improve aileron control effectiveness at high angles of attack during an approach to a stall.
A fabric skin with an aluminum frame that produces the lift necessary to support the WSC in flight; including the flight wires/control frame below and the ground wires/king post above.

WINGS Program.
A program that encourages general aviation pilots to continue training and provides an opportunity to practice selected maneuvers in a minimum of instruction time. Participation in the WINGS program relieves a pilot from compliance with flight review requirements, provided all WINGS requirements are met. Previously governed by Advisory Circular 61-91, the WINGS program is available as on online education program at www.faasafety.gov, effective mid-2007.

Airfoils attached to each side of the fuselage and are the main lifting surfaces that support the airplane in flight.

The maximum distance from wingtip to wingtip.

Wingtip vortices
The rapidly rotating air that spills over an aircraft’s wings during flight. The intensity of the turbulence depends on the aircraft’s weight, speed, and configuration. It is also referred to as wake turbulence. Vortices from heavy aircraft may be extremely hazardous to small aircraft.

a. As a request: Communication is difficult. Please say every phrase twice. b. As information: Since communications are difficult, every phrase in this message will be spoken twice.

A measurement of force used to produce movement.

Working or short-term memory.
The portion of the brain that receives information from the sensory register. This portion of the brain can store information in memory for only a short period of time. If the information is determined by an individual to be important enough to remember, it must be coded in some way for transmittal to long-term memory.

World Aeronautical Charts
(WAC) (1:1,000,000) 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, principal roads, railroads, distinctive landmarks, drainage, and relief. Aeronautical information includes visual and radio aids to navigation, airports, airways, restricted areas, obstructions, and other pertinent data.


See weight-shift control.