V$_{NE}$. The never-exceed speed. Operating above this speed is prohibited since it may result in damage or structural failure. The red line on the airspeed indicator. 

V$_{NO}$. The maximum structural cruising speed. Do not exceed this speed except in smooth air. The upper limit of the green arc. 

VOR.  See very-high frequency omnidirectional range. 

VORTAC.  A facility consisting of two components, VOR and TACAN, which provides three individual services: VOR azimuth, TACAN azimuth, and TACAN distance (DME) at one site. 

VOR test facility (VOT).  A ground facility which emits a test signal to check VOR receiver accuracy. Some VOTs are available to the user while airborne, while others are limited to ground use only. 

VOT. See VOR test facility. 

VSI. See vertical speed indicator. 

V$_{S0}$. The stalling speed or the minimum steady flight speed in the landing configuration. In small airplanes, this is the power-off stall speed at the maximum landing weight in the landing configuration (gear and flaps down). The lower limit of the white arc. 

V$_{S1}$. The stalling speed or the minimum steady flight speed obtained in a specified configuration. For most airplanes, this is the power-off stall speed at the maximum takeoff weight in the clean configuration (gear up, if retractable, and flaps up). The lower limit of the green arc. 

V-tail. A design which utilizes two slanted tail surfaces to perform the same functions as the surfaces of a conventional elevator and rudder configuration. The fixed surfaces act as both horizontal and vertical stabilizers. 

V$_{X}$. Best angle-of-climb speed. The airspeed at which an airplane gains the greatest amount of altitude in a given distance. It is used during a short-field takeoff to clear an obstacle. 

$_{ }$ V$_{Y}$. Best rate-of-climb speed. This airspeed provides the most altitude gain in a given period of time. 

V$_{YSE}$. Best rate-of-climb speed with one engine inoperative. This airspeed provides the most altitude gain in a given period of time in a light, twin-engine airplane following an engine failure. 

## W 

WAAS.  See wide area augmentation system. 

Wake turbulence.  Wingtip vortices that are created when an airplane generates lift. When an airplane 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.  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. 

WARP. See weather and radar processing. 

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. 

Waypoint. A designated geographical location used for route definition or progress-reporting purposes and is defined in terms of latitude/longitude coordinates. 

WCA.  See wind correction angle. 

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

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

Wide area augmentation system (WAAS).  A differential global positioning system (DGPS) that improves the accuracy of the system by determining position error from the GPS satellites, then transmitting the error, or corrective factors, to the airborne GPS receiver. 

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. 

