VFR over-the-top.  A VFR operation in which an aircraft operates in VFR conditions on top of an undercast. 

Victor airways.  Airways based on a centerline that extends from one VOR or VORTAC navigation aid or intersection, to another navigation aid (or through several navigation aids or intersections); used to establish a known route for en route procedures between terminal areas. 

Visual approach slope indicator (VASI).  A visual aid of lights arranged to provide descent guidance information during the approach to the runway. A pilot on the correct glide slope will see red lights over white lights. 

Visual descent point (VDP).  A defined point on the final approach course of a nonprecision straight-in approach procedure from which normal descent from the MDA to the runway touchdown point may be commenced, provided the runway environment is clearly visible to the pilot. 

Visual flight rules (VFR). Flight rules adopted by the FAA governing aircraft flight using visual references. VFR operations specify the amount of ceiling and the visibility the pilot must have in order to operate according to these rules. When the weather conditions are such that the pilot can not operate according to VFR, he or she must use instrument flight rules (IFR). 

Visual meteorological conditions (VMC).  Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling meeting or exceeding the minimums specified for VFR. 

VMC.  See visual meteorological conditions. 

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. 

WAAS.  See wide area augmentation system. 

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. 

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). 

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. 

Wind shear. A change in wind speed and/or wind direction in a short distance. 

Work.  A measurement of force used to produce movement. 

Zone of confusion.  Volume of space above the station where a lack of adequate navigation signal directly above the VOR station causes the needle to deviate. 

