V1
See takeoff decision speed.

V2
See takeoff safety speed.

VA
The design maneuvering speed. The maximum speed at which full, abrupt control movement can be used without overstressing the airframe.

VAD winds
In weather; velocity azimuth display winds are derived from the output of the 160 or more WRS-88 radar sites located throughout the United States. The WRS-88 is configured to produce radar returns off of dust and other particulate matter in the air, and in turn, those returns can be used to indicate wind direction and speed at different altitudes. Generally reported in 1000 foot increments.

Validity
The extent to which a test measures what it is supposed to measure.

Vapor lock
A problem that mostly affects gasoline-fuelled internal combustion engines. It occurs when the liquid fuel changes state from liquid to gas while still in the fuel delivery system. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carburetor or fuel injection system,
resulting in transient loss of power or complete stalling. Restarting the engine from this state may be difficult. The fuel can vaporise due to being heated by the engine, by the local climate, or due to a lower boiling point at high altitude.

VARIATION
-The angular difference
between true north and magnetic
north; indicated on charts by isogonic
lines.

Variation.
Compass error caused by the difference in the physical locations of the magnetic north pole and the geographic north pole.

Variometer.
Sensitive rate of climb or descent indicator
that measures static pressure between the static ports and
an external capacity. Variometers can be mechanical or
electrical and can be compensated to eliminate unrealistic
indications of lift and sink due to rapid speed changes.

VASI
See visual approach slope indicator.

VCOA
(See VISUAL CLIMB OVER AIRPORT.)
VDP
See visual descent point.

VECTOR
A heading issued to an aircraft to provide navigational guidance by radar. (See ICAO term RADAR VECTORING.)

Vector
A force vector is a graphic representation of a force and shows both the magnitude and direction of the force.

Vectoring
Navigational guidance by assigning headings.

Vehicle
Manmade means of transportation; an ultralight
aircraft (not a light-sport aircraft).

Velocity.
The speed or rate of movement in a certain direction.

Vent line.
The line that activates the cooling vent.
Vent.
(1) The action of opening the vent to cool the air in the envelope. (2) An envelope opening that will automatically close.

Venturi Effect
The effect of Bernoulli’s principle, which
states that the pressure of a fluid decreases as it is speeded up
without losing or gaining any energy from the outside.

Venturi tube.
A specially shaped tube attached to the outside of an aircraft to produce suction to allow proper operation of gyro instruments.

Venturi
A specially shaped restriction in a tube designed
to speed up the flow of fluid passing through in accordance
with Bernoulli’s principle. Venturis are used in carburetors
and in many types of fluid control devices to produce a
pressure drop proportional to the speed of the fluid passing
through them.

Verified
Confirmation of information or configuration status.

VERIFY
Request confirmation of information; e.g., verify assigned altitude.

VERIFY SPECIFIC DIRECTION OF TAKEOFF (OR TURNS AFTER TAKEOFF)
Used by ATC to ascertain an aircrafts direction of takeoff and/or direction of turn after takeoff. It is normally used for IFR departures from an airport not having a control tower. When direct communication with the pilot is not possible, the request and information may be relayed through an FSS, dispatcher, or by other means. (See IFR TAKEOFF MINIMUMS AND DEPARTURE PROCEDURES.)

VERTEX
The last fix adapted on the arrival speed segments. Normally, it will be the outer marker of the runway in use. However, it may be the actual threshold or other suitable common point on the approach path for the particular runway configuration.

VERTEX TIME OF ARRIVAL
A calculated time of aircraft arrival over the adapted vertex for the runway configuration in use. The time is calculated via the optimum flight path using adapted speed segments.

Vertical axis (yaw)
An imaginary line passing vertically through the center of gravity of an aircraft. The vertical axis is called the z-axis or the yaw axis.

Vertical card compass.
A magnetic compass that consists of an azimuth on a vertical card, resembling a heading indicator with a fixed miniature airplane to accurately present the heading of the aircraft. The design uses eddy current damping to minimize lead and lag during turns.

VERTICAL NAVIGATION (VNAV)
A function of area navigation (RNAV) equipment which calculates, displays, and provides vertical guidance to a profile or path

VERTICAL SEPARATION
Separation between aircraft expressed in units of vertical distance. (See SEPARATION.)

Vertical shear
See Wind shear.

Vertical speed indicator (VSI)
An instrument that uses static pressure to display a rate of climb or descent in feet per minute. The VSI can also sometimes be called a vertical velocity indicator (VVI).

Vertical stability.
Stability about an aircraft’s vertical axis. Also called yawing or directional stability.

VERTICAL TAKEOFF AND LANDING AIRCRAFT
Aircraft capable of vertical climbs and/or descents and of using very short runways or small areas for takeoff and landings. These aircraft include, but are not limited to, helicopters. (See SHORT TAKEOFF AND LANDING AIRCRAFT.)

VERTICAL VIBRATION
A vibration in which the movement is up and down, or vertical, as in an out-of-track condition.

Vertically propagating wave
An atmospheric disturbance in the lee of a mountain or ridge that develops and transports its energy vertically.

Vertigo
A type of spatial disorientation caused by the physical senses sending conflicting signals to the brain. Vertigo is especially hazardous when flying under conditions of poor visibility and may cause pilot incapacitation, but may be minimized by confidence in the indication of the flight instruments.

VERY HIGH FREQUENCY
The frequency band between 30 and 300 MHz. Portions of this band, 108 to 118 MHz, are used for certain NAVAIDs; 118 to 136 MHz are used for civil air/ground voice communications. Other frequencies in this band are used for purposes not related to air traffic control.

VERY HIGH FREQUENCY OMNIDIRECTIONAL RANGE STATION
(See VOR.)

VERY LOW FREQUENCY
The frequency band between 3 and 30 kHz.

Very-high frequency (VHF).
A band of radio frequencies falling between 30 and 300 MHz.

Very-high frequency omnidirectional range (VOR).
Electronic navigation equipment in which the flight deck instrument identifies the radial or line from the VOR station, measured in degrees clockwise from magnetic north, along which the aircraft is located.

Very-high frequency Omni directional Range (VOR).
Electronic navigation equipment in which the flight deck instrument identifies the radial or line from the VOR station,
measured in degrees clockwise from magnetic north, along which the aircraft is located.

VESSEL
Anything capable of being used for transportation on water, including seaplanes.

Vestibule.
The central cavity of the bony labyrinth of the ear, or the parts of the membranous labyrinth that it contains.

VFE.
The maximum speed with the flaps extended. The upper limit of the white arc.

VFR
(See VISUAL FLIGHT RULES.)

VFR AIRCRAFT
An aircraft conducting flight in accordance with visual flight rules. (See VISUAL FLIGHT RULES.)

VFR CONDITIONS
Weather conditions equal to or better than the minimum for flight under visual flight rules. The term may be used as an ATC clearance/instruction only when: a. An IFR aircraft requests a climb/descent in VFR conditions. b. The clearance will result in noise abatement benefits where part of the IFR departure route does not conform to an FAA approved noise abatement route or altitude. c. A pilot has requested a practice instrument approach and is not on an IFR flight plan. Note: All pilots receiving this authorization must comply with the VFR visibility and distance from cloud criteria in 14 CFR Part 91. Use of the term does not relieve controllers of their responsibility to separate aircraft in Class B and Class C airspace or TRSAs as required by FAAO JO 7110.65. When used as an ATC clearance/instruction, the term may be abbreviated VFR; e.g., MAINTAIN VFR, CLIMB/DESCEND VFR, etc.

VFR FLIGHT
(See VFR AIRCRAFT.)

VFR MILITARY TRAINING ROUTES
Routes used by the Department of Defense and associated Reserve and Air Guard units for the purpose of conducting low-altitude navigation and tactical training under VFR below 10,000 feet MSL at airspeeds in excess of 250 knots IAS.

VFR NOT RECOMMENDED
An advisory provided by a flight service station to a pilot during a preflight or inflight weather briefing that flight under visual flight rules is not recommended. To be given when the current and/or forecast weather conditions are at or below VFR minimums. It does not abrogate the pilots authority to make his/her own decision.

VFR on top.
ATC authorization for an IFR aircraft to operate in VFR conditions at any appropriate VFR altitude.

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

VFR terminal area chart.
At a scale of 1:250,000, a chart that depicts Class B airspace, which provides for the control or segregation of all the aircraft within the Class B airspace. The chart depicts topographic information and aeronautical information including visual and radio aids to navigation, airports, controlled airspace, restricted areas, obstructions, and related data.

VFR WAYPOINT
(See WAYPOINT.)

VFR
See visual flight rules.

VFR/VFR
Traffic advisories and, as appropriate, safety alerts. The normal radius will be 20 nautical miles with some variations based on site-specific requirements. The outer area extends outward from the primary Class C airspace airport and extends from the lower limits of radar/radio coverage up to the ceiling of the approach controls delegated airspace excluding the Class C charted area and other airspace as appropriate. (See CONFLICT RESOLUTION.) (See CONTROLLED AIRSPACE.)

VFR-ON-TOP
ATC authorization for an IFR aircraft to operate in VFR conditions at any appropriate VFR altitude (as specified in 14 CFR and as restricted by ATC). A pilot receiving this authorization must comply with the VFR visibility, distance from cloud criteria, and the minimum IFR altitudes specified in 14 CFR Part 91. The use of this term does not relieve controllers of their responsibility to separate aircraft in Class B and Class C airspace or TRSAs as required by FAAO JO 7110.65.

VFR-on-top.
ATC authorization for an IFR aircraft to operate in VFR conditions at any appropriate VFR altitude.

V-G diagram.
A chart that relates velocity to load factor. It is valid only for a specific weight, configuration and altitude and shows the maximum amount of positive or negative lift the airplane is capable of generating at a given speed. Also shows the safe load factor limits and the load factor that the aircraft can sustain at various speeds.

VHF
(See VERY HIGH FREQUENCY.)

VHF OMNIDIRECTIONAL RANGE/TACTICAL AIR NAVIGATION
(See VORTAC.)

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.

VIDEO MAP
An electronically displayed map on the radar display that may depict data such as airports, heliports, runway centerline extensions, hospital emergency landing areas, NAVAIDs and fixes, reporting points, airway/route centerlines, boundaries, handoff points, special use tracks, obstructions, prominent geographic features, map alignment indicators, range accuracy marks, minimum vectoring altitudes.

Virga.
Precipitation that falls from a cloud and evaporates before reaching the ground.

Virtual Reality (VR).
A form of computer-based technology that creates a sensory experience allowing a participant to believe and barely distinguish a virtual experience from a real one. VR uses graphics with animation systems, sounds, and images to reproduce electronic versions of real-life experience.

VISIBILITY
The ability, as determined by atmospheric conditions and expressed in units of distance, to see and identify prominent unlighted objects by day and prominent lighted objects by night. Visibility is reported as statute miles, hundreds of feet or meters. (Refer to 14 CFR Part 91.) (Refer to AIM.)

VISIBILITY [ICAO]
The ability, as determined by atmospheric conditions and expressed in units of distance, to see and identify prominent unlighted objects by day and prominent lighted objects by night. a.

VISUAL APPROACH
An approach conducted on an instrument flight rules (IFR) flight plan which authorizes the pilot to proceed visually and clear of clouds to the airport. The pilot must, at all times, have either the airport or the preceding aircraft in sight. This approach must be authorized and under the control of the appropriate air traffic control facility. Reported weather at the airport must be ceiling at or above 1,000 feet and visibility of 3 miles or greater. (See ICAO term VISUAL APPROACH.)

VISUAL APPROACH [ICAO]
An approach by an IFR flight when either part or all of an instrument approach procedure is not completed and the approach is executed in visual reference to terrain.

VISUAL APPROACH SLOPE INDICATOR
(See AIRPORT LIGHTING.)

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 CLIMB OVER AIRPORT (VCOA)
A departure option for an IFR aircraft, operating in visual meteorological conditions equal to or greater than the specified visibility and ceiling, to visually conduct climbing turns over the airport to the published climb-to altitude from which to proceed with the instrument portion of the departure. VCOA procedures are developed to avoid obstacles greater than 3 statute miles from the departure end of the runway as an alternative to complying with climb gradients greater than 200 feet per nautical mile.

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
Rules that govern the procedures for conducting flight under visual conditions. The term VFR is also used in the United States to indicate weather conditions that are equal to or greater than minimum VFR requirements. In addition, it is used by pilots and controllers to indicate type of flight plan. (See INSTRUMENT FLIGHT RULES.) (See INSTRUMENT METEOROLOGICAL CONDITIONS.) (See VISUAL METEOROLOGICAL CONDITIONS.) (Refer to 14 CFR Part 91.) (Refer to AIM.)

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 HOLDING
The holding of aircraft at selected, prominent geographical fixes which can be easily recognized from the air. (See HOLDING FIX.)

VISUAL METEOROLOGICAL CONDITIONS
Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling equal to or better than specified minima. (See INSTRUMENT FLIGHT RULES.) (See INSTRUMENT METEOROLOGICAL CONDITIONS.) (See VISUAL FLIGHT RULES.)
Visual meteorological conditions (VMC)
Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling meeting or exceeding the minimums specified for VFR.

VISUAL SEGMENT
(See PUBLISHED INSTRUMENT APPROACH PROCEDURE VISUAL SEGMENT.)

VISUAL SEPARATION
A means employed by ATC to separate aircraft in terminal areas and en route airspace in the NAS. There are two ways to effect this separation: a. The tower controller sees the aircraft involved and issues instructions, as necessary, to ensure that the aircraft avoid each other. b. A pilot sees the other aircraft involved and upon instructions from the controller provides his/her own separation by maneuvering his/her aircraft as necessary to avoid it. This may involve following another aircraft or keeping it in sight until it is no longer a factor. (See SEE AND AVOID.) (Refer to 14 CFR Part 91.)

VLE
Landing gear extended speed. The maximum speed at which an airplane can be safely flown with the landing gear extended.

VLF
(See VERY LOW FREQUENCY.)

VLO.
Landing gear operating speed. The maximum speed for extending or retracting the landing gear if using an airplane equipped with retractable landing gear.

VMC.
Minimum control airspeed. This is the minimum flight speed at which a light, twin-engine airplane can be satisfactorily controlled when an engine suddenly becomes inoperative and the remaining engine is at takeoff power.

VNE
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.

VNO
The maximum structural cruising speed. Do not exceed this speed except in smooth air. The upper limit of the green arc.

VOICE SWITCHING AND CONTROL SYSTEM
The VSCS is a computer controlled switching system that provides air traffic controllers with all voice circuits (air to ground and ground to ground) necessary for air traffic control. (See VOICE SWITCHING AND CONTROL SYSTEM.) (Refer to AIM.)

Volume.
The total amount of air or gas (expressed in cubic feet) contained in a balloon envelope.

VOR
A ground-based electronic navigation aid transmitting very high frequency navigation signals, 360 degrees in azimuth, oriented from magnetic north. 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. (See NAVIGATIONAL AID.) (Refer to AIM.)
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.

VOR TEST SIGNAL
(See VOT.)

VOR.
See very-high frequency omnidirectional range.

VOR. REPORTING POINT
A geographical location in relation to which the position of an aircraft is reported. (See COMPULSORY REPORTING POINTS.) (See ICAO term REPORTING POINT.) (Refer to AIM.)

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.

Vortex
an atmospheric disturbance that possesses rotational motion.

VORTEX RING STATE
A transient condition of downward flight (descending through air after just previously being accelerated downward
by the rotor) during which an appreciable portion of the main rotor system is being forced to operate at angles of attack above maximum. Blade stall starts near the hub and progresses outward as the rate of descent increases.

VORTICES
Circular patterns of air created by the movement of an airfoil through the air when generating lift. As an airfoil moves through the atmosphere in sustained flight, an area of area of low pressure is created above it. The air flowing from the high pressure area to the low pressure area around and about the tips of the airfoil tends to roll up into two rapidly rotating vortices, cylindrical in shape. These vortices are the most predominant parts of aircraft wake turbulence and their rotational force is dependent upon the wing loading, gross weight, and speed of the generating aircraft. The vortices from medium to heavy aircraft can be of extremely high velocity and hazardous to smaller aircraft. (See AIRCRAFT CLASSES.) (See WAKE TURBULENCE.) (Refer to AIM.)

VOT
A ground facility which emits a test signal to check VOR receiver accuracy. Some VOTs are available to the user while airborne, and others are limited to ground use only. (See AIRPORT/FACILITY DIRECTORY.) (Refer to 14 CFR Part 91.) (Refer to AIM.)

VR
(See VFR MILITARY TRAINING ROUTES.)

VS
See stalling speed.

VS0.
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.

VS1.
The stalling speed or the minimum steady flight speed obtained in aspecified 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.

VSCS
(See VOICE SWITCHING AND CONTROL SYSTEM.)

VSI
See vertical speed indicator.

VSI.
See vertical speed indicator.

VTA
(See VERTEX TIME OF ARRIVAL.)

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.

VTOL AIRCRAFT
(See VERTICAL TAKEOFF AND LANDING AIRCRAFT.)

VX
See best angle-of-climb speed.

VX
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.

VY
See best rate-of-climb speed.

VY
Best rate-of-climb speed. This airspeed provides the most altitude gain in a given period of time.

VYSE
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.