the Aviation Dictionary

vertical visibility . VHF omni-directional range /tactical air navigation (VORTAC)
vertical visibility - The distance one can see upward
into a surface based obscuration; or the maximum
height from which a pilot in flight can recognize the
ground through a surface based obscuration.
vertical wind shear - The change in wind speed andlor
direction over a vertical distance. See also wind shear.
vertigo - Spatial disorientation caused by the physical
senses sending signals to the brain that create a feeling
of whirling and dizziness.
very high frequency - The frequency band between 30
and 300 MHz. Portions of this band, 108 to I 18 MHz,
are used for certain NAVAIDs; 118 to 136 MHz are
used for civil airlground voice communications. Other
frequencies in this band are used for purposes not
related to air traf'fic control.
very high frequency omni-directional range station -
The omni-directional, or all-directional, range station
provides the pilot with a course from any point within
its service range It produces 360 usable radials or
courses, any one of which is a radio path connected to
the station. The radials can be considered as lines that
extend from the transmitter antenna like spokes of a
wheel. Operation is in the VHF portion of the radio
spectrum (frequency range of 109.0- 1 17.95 MHz).
very high frequency omnirange (VOR) navigation
equipment - The omni-directional, or all-directional,
range station provides the pilot with a course from any
point within its service range It produces 360 usable
radials or courses, any one of which is a radio path
connected to the station. The radials can be considered
as lines that extend from the transmitter antenna like
spokes of a wheel. Operation is in the VHF portion of
the radio spectrum (frequency range of 109.0- 1 17.95
MHz).
very low frequency (VLF) - The radio frequency range
between 3 and 30 kHz.
VFR aircraft - An aircraft conducting flight in
accordance with visual flight rules.
VFR conditions - Weather conditions equal to or better
than the minimum for flight under visual flight rules.
The term can be used as an ATC clearancelinstruction
only when:
a. An IFR aircraft requests a climbldescent 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.
All pilots receiving this authorization must comply with
the VFR visibility and distance from cloud criteria in
FAR 91. Use of the term does not relieve controllers of
their responsibility to separate aircraft in Class B and
Class C airspace or TRSA's as required by FAA Order
71 10.65. When used as an ATC clearance/instruction,
the term can be abbreviated "VFR"; e.g., "MANTAIN
VFR," "CLIMB1 DESCEND VFR," etc.
VFR cruising altitude - When flying above 3,000 feet
AGL on a magnetic heading of Ob to 179" you must fly
at odd thousand-foot altitudes plus 500 feet and on a
heading of 180" to 359' you are required to fly on even
thousands plus 500 feet up to the flight levels.
VFR flight - Flight in accordance with visual flight
rules.
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. [Jeppesen does not chart these routes]
VFR not recommended - An advisory provided by a
flight service station to a pilot during a pre-flight or
inflight weather briefing that flight under visual flight
rules is not recommended. To be given when the
current andor forecast weather conditions are at or
below VFR minimums. It does not abrogate the pilot's
authority to make his own decision.
VFR over-the-top - With respect to the operation of
aircraft, means the operation of an aircraft over-the-top
under VFR when it is not being operated on an IFR
flight plan.
VFR terminal area charts - Depict Class B airspace
that provides for the control or segregation of all the
aircraft within the Class B airspace. The charts depict
topographic information and aeronautical information
that includes visual and radio aids to navigation,
airports, controlled airspace, restricted areas,
obstructions, and related data.
VFR waypoint - A predetermined geographical position
used for routelinstrument approach definition, progress
reports, published VFR roites, visual reporting
or points for transitioning, andlor circumnavigating
controlled andor special use airspace. Defined relative
to a VORTAC station or in terms of latitudeilongitude
coordinates.
VFR-on-top - ATC authorization for an IFR aircraft to
operate in VFR conditions at any appropriate VFR
altitude (as specified in FAR 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 FAR 91.
The use of this term does not relieve controllers of their
responsibility to separate aircraft in Class B and Class
C airspace or TRSA's as required by FAA Order
71 10.65.
VHF omni-directional range /tactical air navigation
(VORTAC) - A navigation aid providing VOR
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