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

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

Vertical axis.  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 speed indicator (VSI). A rate-of-pressure change instrument that gives an indication of any deviation from a constant pressure level. 

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

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. 

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

V$_{FE}$. The maximum speed with the flaps extended. The upper limit of the white arc. 

VFR.  See visual flight rules. 

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. 

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. 

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 glideslope 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 cannot 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. 

V$_{LE}$. Landing gear extended speed. The maximum speed at which an airplane can be safely flown with the landing gear extended. 

V$_{LO}$. Landing gear operating speed. The maximum speed for extending or retracting the landing gear if using an airplane equipped with retractable landing gear. 

V$_{MC}$. 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. 

VMC.  See visual meteorological conditions. 

