V Victor

valley wind - It is formed during the day by the heating of the valley floor. As the ground becomes warmer than the surrounding atmosphere, the lower levels of air heat and rise, flowing up the mountainsides. It blows in the opposite direction of a mountain breeze.

variable sweep wing - Wings that are hinged so they can be slanted forward or backward during flight. The F-14 aircraft is an example of a supersonic jet with variable sweep wings.

vector - A heading issued to an aircraft by ATC to provide navigational guidance by radar.

vector line - This is a course line that is predicted within a specified number of minutes assuming the aircraft's course is not changed.

velocity - The speed of an object, in a certain direction. The rate of change of position in relation to time.

vertical axis - The axis extending straight up and down through the center of gravity of an aircraft. The vertical axis is perpendicular to the longitudinal and lateral axes. The vertical axis is sometimes called the "z" axis. Yaw is a motion around the vertical axis.

vertical stabilizer - The vertical part of the tail. The vertical stabilizer helps to increase the stability of the aircraft. It is also known as a fin.

VFR (Visual Flight Rules) - Rules that govern the procedures for conducting flight in visual conditions. The term "VFR" is also used to indicate weather conditions that comply with specified VFR requirements.

Victor - Designator for the letter "V" in the International Phonetic Alphabet.

Victor airway - An airway system based on the use of VOR facilities. The north-south airways have odd numbers (Victor 11), and the east-west airways have even numbers (Victor 14).

visibility - A measure of the opacity of the atmosphere, and therefore, the greatest distance one can see prominent objects with normal eyesight. The National Weather Service has various terms for visibility. Surface visibility is the prevailing visibility determined from the usual point of observation. Prevailing visibility is considered representative of visibility conditions at the station. Sector visibility is the visibility in a specified direction that represents at least a 45 degree arc of the horizon circle. Tower visibility is the prevailing visibility determined from the airport traffic control tower (ATCT) at stations that also report surface visibility.

visual flight - A flight made by referencing the horizon and other outside landmarks.

VMC (Visual Meteorological Conditions) - Meteorological conditions expressed in terms of visibility, distance from clouds, and ceiling equal to or better than specified minimal.

VOR (Very high frequency Omni-directional Range) - A ground-based electronic navigation aid transmitting very high frequency navigation signals. These signals radiate out completely around 360 degrees in azimuth, oriented from magnetic north. VOR is used as the basis for navigation in the National Airspace System. The VOR periodically identifies itself by Morse Code and may have an additional voice identification feature. Voice features may be used by ATC or FSS for transmitting instructions/information to pilots.

VOR receiver - This cockpit device receives VOR signals and allows to pilots to select and maintain their magnetic compass course.

VOR station - A ground station that transmits VOR signals.

VORTAC - A navigational aid providing VOR azimuth (direction), TACAN azimuth, and distance measuring equipment (DME) at one site.

vortices - See wingtip vortices

VTOL (Vertical TakeOff and Landing) - Aircraft that have the capability of vertical takeoff and landing. VTOL aircraft are not limited to helicopters.