Airway (aviation)
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In aviation, an airway is a designated route in the air. Airways are laid out between navigational aids such as VORs, NDBs and Intersections (NDB-based airways are rare in the United States, but are more common in much of the rest of the world).
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[edit] United States
The earliest airways in the United States were constructed by the US Post Office to guide airmail pilots on their delivery routes. These airways were between major cities and identified at night by a series of flashing lights and beacons which pilots flew over in sequence to get from one city to the next.[citation needed] However, these visual airways still required the pilots to be in visual contact with the ground which precluded flying in fog or clouds. Subsequently, the Department of Commerce funded the development of other means of airway navigation.[1]
The first radiofrequency coordinated airways were first based on the old A-N Morse code system. The pilot will listen for either the Morse code for A or N and the objective was to hear a steady tone (the A-N Morse codes are exactly opposite each other). Later on, the airways were based on Low / Medium Frequency ground stations, like the beat frequency oscillator (BFO) and the non-directional beacon (NDB). These L/M frequency airways were the colored airways. There are still colored airways in existence today, mostly in Alaska. There is one colored airway off the coast of North Carolina called G13 or Green 13.
In the United States, low altitude airways (below 18,000 feet (5,500 m) MSL), appear on sectional charts, world aeronautical charts and en route low altitude charts and are designated by the letter "V" (pronounced Victor, hence Victor airways). High altitude airways (above 18,000 feet (5,500 m) MSL), called jet routes, appear on high altitude charts (that usually don't show topography, as the low altitude charts do) and are designated by the letter "J".
With the invention of RNAV routes, the airway structure no longer has to be based on ground based navaids and a new naming convention is used. RNAV routes not based on VOR routes in low altitudes are preceded with the letter "T" while High airway routes are designated with the letter "Q". These RNAV routes are blue on low and high en-route charts produced by National Aeronautical Charting Office (NACO).
In the United States, Victor airways are Class E airspace from 1,200 feet (370 m) AGL to 18,000 feet (5,500 m) MSL. The width of the victor corridor depends on the distance from the navigational aids (such as VOR's and NDB's). When VOR's are less than 102 NM from each other, the Victor airway extends 4 NM on either side of the center line (8 NM total width). When VOR's 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 on either side of the center line between the two navaids (at 51 NM from a navaid, 4.5 degrees from the center line 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 navaids.
[edit] Europe
In Europe, airways are corridors 10 nautical miles (19 km) wide of controlled airspace with a defined lower base, usually FL070-FL100, extending to FL195. They link the major airports giving protection to IFR flights during the climb and descent phases, and often for non-jet aircraft, cruise phases of flight. Historically they were laid out between VORs; however, advances in navigational technology mean that nowadays this is not always the case. Like European roads, each airway has a designator containing one letter and one to three numbers. All airspace above FL195 is class C controlled airspace, the equivalent to airways being called Upper Air Routes and having designators prefixed with the letter "U". If an upper air route follows the same track as an airway its designator will be identical to the airway, prefixed with the letter "U".
In the UK, airways are all Class A below FL195 and therefore VFR flights are prohibited.
