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.  VMC.  See visual meteorological conditions.  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.  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$_{LE}$.  Landing gear extended speed. The maximum speed at  which an airplane can be safely flown with the landing gear  extended.  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 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 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 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.  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.  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.  G-33 