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visual approach (air traffic control). 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, and the reported weather at the airport must be:
ceiling at or above 1,000 feet and visibility of three miles or greater.
vitrify. To turn a material into a glasslike substance by heating it enough so that it melts.
vixen file. A metal-cutting hand file that has curved teeth across its faces. Vixen files are used to remove
large amounts of soft metal.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 620
VLF (very-low frequency) (radio frequencies). The range of radio frequencies between three kilohertz
(3,000 cycles per second) and 30 kilohertz (30,000 cycles per second). VLF radio waves are used for
operations that require the signal to travel great distances.
VNE (never-exceed speed). The maximum speed an aircraft is allowed to attain in any conditions of flight.
VNE is marked on the airspeed indicator with a red radial line.
volatile liquid. A liquid that evaporates easily, or readily turns into a vapor. Alcohol and gasoline are both
volatile liquids.
volatile memory (computer memory). Memory in a computer in which all data is lost when power to the
computer is turned off. Dynamic RAMs (random access memories) store data in the form of charges on
capacitors. Memory stored in this manner is volatile.
volatility. The characteristic of a liquid that relates to its ability to vaporize, or change into a gas.
volt (electrical unit). The basic unit of electrical pressure. One volt is the amount of electrical pressure
needed to force one ampere of current through a resistance of one ohm. One volt is also the amount of
electrical pressure drop that occurs when a current of one ampere produces one watt of power.
voltage amplifier (electronic circuit). An electronic circuit capable of increasing voltage. Voltage
amplifiers normally supply an extremely small amount of current.
voltage divider (electrical circuit). An electrical circuit in which a tapped resistor or a series of resistors is
installed across a voltage source to provide various output voltages. The sum of the voltage drops across
each of the resistances in a voltage divider is the same as the voltage across the entire resistance.
voltage doubler (electrical circuit). An electrical circuit in which alternating current is rectified, and its
output is increased to a value of twice its original peak value.
voltage drop. The drop in voltage or electrical pressure caused by current flowing through a resistance. A
voltage drop is called an IR (current times resistance) drop.
voltage quadrupler (electrical circuit). An electrical circuit in which alternating current is rectified, and
its output is increased to a value four times its original peak value.
voltage regulator (generator or alternator control). A device which holds the output voltage of a
generator or alternator constant as its speed changes in normal operation and its load current changes within
its rated value.
voltage regulator tube (electron tube). A special gas-filled electron tube. The tube, in series with a
resistor, is placed across the output of a DC power supply. The gas in the tube ionizes when a specific
voltage is placed across it, and when the gas ionizes, electrons flow through it with very little opposition.
The voltage drop across the regulator tube remains constant as the load current changes.
voltage spike (electrical disturbance). A sudden, short-duration surge of high voltage along a power line
or in a piece of electrical equipment. Voltage spikes are induced into the system by lightning or by some
inductive equipment being turned off. These high-voltage spikes can damage many types of semiconductor
devices.
Surge protectors are used to bypass voltage spikes to ground, so they cannot cause damage.
voltammeter (electrical measuring instrument). An instrument that can measure both volts and amperes.
A switch is built into the instrument to change its function.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 621
volt-amp. The basic unit of apparent power in an AC circuit. A volt-amp is the product of the circuit
voltage and all of the current, regardless of its phase. A volt-amp differs from a watt in that a watt is a
measure of true power and is the product of the circuit voltage and only that current in phase with it.
voltmeter. An electrical measuring instrument used to measure electrical pressure. Most of the commonly
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