Victor airways are pre-determined routes flown by pilots under instrument flight rules

Instrument flight rules

Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....

 (IFR). They are defined by VHF omnidirectional range

VHF omnidirectional range

VOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...

 (VOR) radials and have established minimum (and possibly maximum) altitudes at which they may be flown. Victor airways are depicted as black solid lines on IFR Low-Altitude Enroute charts and as thick faded blue lines on VFR Terminal and Sectional Area charts. They may be likened as "highways in the sky" and are identified by a number, similar to an interstate highway (for example, a pilot could say that he/she is "flying Victor Eight").

Victor airways are, by definition, surrounded by Class E airspace from 1200 feet (365.8 m) above ground level (AGL)

Above ground level

In aviation and atmospheric sciences, an altitude is said to be above ground level when it is measured with respect to the underlying ground surface. This is as opposed to above mean sea level , or in broadcast engineering, height above average terrain...

 up to, but not including, 18000 feet (5,486.4 m) above mean sea level (AMSL)

Above mean sea level

The term above mean sea level refers to the elevation or altitude of any object, relative to the average sea level datum. AMSL is used extensively in radio by engineers to determine the coverage area a station will be able to reach...

. These virtual airways are defined primarily by VORs, and comprise a system of established routes that run along specified VOR radials, hence the beginning letter V (see NATO Phonetic alphabet).

The width of the victor corridor depends on the distance from the navigational aid

Navigational aid

A navigational aid is any sort of marker which aids the traveler in navigation; the term is most commonly used to refer to nautical or aviation travel...

s (such as VORs and non-directional beacon

Non-directional beacon

A non-directional beacon is a radio transmitter at a known location, used as an aviation or marine navigational aid. As the name implies, the signal transmitted does not include inherent directional information, in contrast to other navigational aids such as low frequency radio range, VHF...

s (NDBs):

• When VORs are less than 102 nautical mile
  Nautical mile
  The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...
  
  s (NM) (189 km) from each other, the Victor airway extends 4 NM (7.4 km) on either side of the center line (8 NM (14.8 km) total width).
• When VORs are more than 102 NM from each other, the width of the airway in the middle increases. The width of the airway beyond 51 NM from a navaid is 4.5 degrees
  Degree (angle)
  A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
  
  on either side of the center line between the two navaids (at 51 NM from a navaid, 4.5 degrees from the centerline of a radial is equivalent to 4 NM). The maximum width of the airway is at the middle point between the two navaids. This is when 4.5 degrees from the center radial results in a maximum distance for both navigational aids.