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.  G-34  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.  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.  Weight.  The force exerted by an aircraft from the pull of  gravity.  Weather depiction chart.  Details surface conditions as  derived from METAR and other surface observations.  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).  WCA.  See wind correction angle.  Waypoint.  A designated geographical location used for route  definition or progress-reporting purposes and is defined in  terms of latitude/longitude coordinates.  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.  WARP.  See weather and radar processing.  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.  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.  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.  WAAS.  See wide area augmentation system.  W 